Paternal country of origin and adverse neonatal outcomes in births to foreign-born women in Norway: A population-based cohort study.

BACKGROUND: Migration is a risk factor for adverse neonatal outcomes. The various impacts of maternal origin have been reported previously. The aim of this study was to investigate associations between paternal origin and adverse neonatal outcomes in births to migrant and Norwegian-born women in Norway. METHODS AND
FINDINGS: This nationwide population-based study included births to migrant (n = 240,759, mean age 29.6 years [±5.3 SD]) and Norwegian-born women (n = 1,232,327, mean age 29.0 years [±5.1 SD]) giving birth in Norway in 1990-2016. The main exposure was paternal origin (Norwegian-born, foreign-born, or unregistered). Neonatal outcomes were very preterm birth (22+0-31+6 gestational weeks), moderately preterm birth (32+0-36+6 gestational weeks), small for gestational age (SGA), low Apgar score (<7 at 5 minutes), and stillbirth. Associations were investigated in migrant and Norwegian-born women separately using multiple logistic regression and reported as adjusted odds ratios (aORs) with 95% confidence intervals (CIs), adjusted for year of birth, parity, maternal and paternal age, marital status, maternal education, and mother's gross income. In births to migrant women, a foreign-born father was associated with increased odds of very preterm birth (1.1% versus 0.9%, aOR 1.20; CI 1.08-1.33, p = 0.001), SGA (13.4% versus 9.5%, aOR 1.48; CI 1.43-1.53, p < 0.001), low Apgar score (1.7% versus 1.5%, aOR 1.14; CI 1.05-1.23, p = 0.001), and stillbirth (0.5% versus 0.3%, aOR 1.26; CI 1.08-1.48, p = 0.004) compared with a Norwegian-born father. In Norwegian-born women, a foreign-born father was associated with increased odds of SGA (9.3% versus 8.1%, aOR 1.13; CI 1.09-1.16, p < 0.001) and decreased odds of moderately preterm birth (4.3% versus 4.4%, aOR 0.95; CI 0.91-0.99, p = 0.015) when compared with a Norwegian-born father. In migrant women, unregistered paternal origin was associated with increased odds of very preterm birth (2.2% versus 0.9%, aOR 2.29; CI 1.97-2.66, p < 0.001), moderately preterm birth (5.6% versus 4.7%, aOR 1.15; CI 1.06-1.25, p = 0.001), SGA (13.0% versus 9.5%, aOR 1.50; CI 1.42-1.58, p < 0.001), low Apgar score (3.4% versus 1.5%, aOR 2.23; CI 1.99-2.50, p < 0.001), and stillbirth (1.5% versus 0.3%, aOR 4.87; CI 3.98-5.96, p < 0.001) compared with a Norwegian-born father. In Norwegian-born women, unregistered paternal origin was associated with increased odds of very preterm birth (4.6% versus 1.0%, aOR 4.39; CI 4.05-4.76, p < 0.001), moderately preterm birth (7.8% versus 4.4%, aOR 1.62; CI 1.53-1.71, p < 0.001), SGA (11.4% versus 8.1%, aOR 1.30; CI 1.24-1.36, p < 0.001), low Apgar score (4.6% versus 1.3%, aOR 3.51; CI 3.26-3.78, p < 0.001), and stillbirth (3.2% versus 0.4%, aOR 9.00; CI 8.15-9.93, p < 0.001) compared with births with a Norwegian-born father. The main limitations of this study were the restricted access to paternal demographics and inability to account for all lifestyle factors.
CONCLUSION: We found that a foreign-born father was associated with adverse neonatal outcomes among births to migrant women, but to a lesser degree among births to nonmigrant women, when compared with a Norwegian-born father. Unregistered paternal origin was associated with higher odds of adverse neonatal outcomes in births to both migrant and nonmigrant women when compared with Norwegian-born fathers. Increased attention to paternal origin may help identify women in maternity care at risk for adverse neonatal outcomes.

Introduction

With an increasing number of babies born to migrant parents, the needs of migrant families in maternity care have been declared a priority for research and action by the World Health Organization [1]. Migrant women have been identified with an increased risk of adverse neonatal outcomes, such as low birthweight [2], small for gestational age (SGA) [3,4], preterm birth [2,5], and perinatal morbidity and mortality [2,6,7]. However, most studies focus on the impact of maternal factors, and less attention has been paid to paternal factors.

Both parents’ origins seem to influence pregnancy outcomes [3,6,8-11]. However, the number of studies investigating paternal origin is limited, and the methodological differences between studies and the complexity of migration all make the findings difficult to interpret [3,6,8-11]. Large population-based studies from Norway, Sweden, Canada, and Australia have shown that a partner from the host population is associated with a decreased risk of very preterm birth [9,10], SGA [3], and stillbirth [6,8,11]. However, the increased risks of preterm birth in general [3,10], moderately preterm birth [9,10], and low Apgar score [3] have been observed irrespective of whether the father is from the host population or not. Further, unregistered paternal origin has been associated with an increased risk of stillbirth [6], and lack of paternal data is acknowledged as an important factor for identifying high-risk pregnant women [12-14]. Other paternal factors associated with neonatal outcomes have also been reported, such as advanced paternal age seeming to increase the risk of preterm birth [15] and stillbirth [16]. Understanding the impact of paternal factors on adverse birth outcomes is not straightforward. There is a need for population-based studies investigating associations between paternal factors, including births when paternal data are missing, and a wider range of adverse neonatal outcomes from a migration perspective.

In this nationwide study, we had access to a standardized collection of population-based data on both maternal and paternal factors, information that is often limited in other studies. To contribute to the understanding of the impact of paternal origin, we investigated the associations between paternal origin (Norwegian-born, foreign-born, or unregistered) and adverse neonatal outcomes (very preterm birth, moderately preterm birth, low Apgar score, and stillbirth) in births to migrant and Norwegian-born women giving birth in Norway between 1990 and 2016. Our hypothesis was that a foreign-born father of the child would be associated with an increased risk of adverse pregnancy outcomes in births to migrant women.

Methods

Study design

This population-based register study included births to migrant women giving birth in Norway between the 1st of January 1990 and 31st of December 2016. Data from the Medical Birth Registry of Norway (MBRN) [17] were linked with data provided by Statistics Norway [18] using each woman’s unique national identity number. Statistics Norway provided data on paternal and maternal country of birth, as well as maternal socioeconomic-related factors. The MBRN provided information on paternal identity and paternal age, as well as data on maternal and infant health, including detailed information on previous pregnancies and births in Norway, though not on births outside of Norway. There was no prospective protocol or analysis plan. The reporting of this study follows the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (S1 STROBE Checklist) [19].

Study population

This study included births to migrant women (n = 240,759 births) and Norwegian-born women (n = 1,232,327) giving birth in Norway in the period 1990–2016 (Fig 1). Migrant women were defined as foreign-born women with 2 foreign-born parents. Births to women born to migrant parents and women with mixed background (migrant women registered with 1 or 2 Norwegian-born parents) or with unknown background, in total 5% of the birth cohort, were excluded to reduce heterogeneity across comparison groups and to simplify interpretation of the results.

Fig 1

Flowchart of the derivation of the study sample (n = 1,620,532).

Setting

In 2018, 29% of all births in Norway were to mothers with a migrant background [20]. Maternity care in Norway is based on the individual woman’s medical needs, and care during pregnancy and birth is free of charge [21]. The healthcare system is considered of high quality, with low maternal and child mortality ratios [22]. However, there are inequalities in healthcare, and migrant women in Scandinavian countries have been found to receive suboptimal care compared with nonmigrant women [23,24]. In Norway, migrant families often struggle economically, and children living in poverty are often children of migrant parents [25].

Paternal factors

Paternal origin was based on information on paternal country of birth retrieved from Statistics Norway (Norwegian-born, foreign-born, or unregistered). Explanation for not being registered in the Statistics Norway may be that the baby’s father was unknown to the mother or that the baby’s father was not a citizen of Norway but still known to the mother. In an effort to distinguish between known and unknown paternal identity, we analyzed a novel variable as derived by the MBRN. In the MBRN, paternal identity (known, unknown) is registered as known when the father’s national identity number or his date of birth has been given by the mother or retrieved from Statistics Norway via routine updates; otherwise, his identity is registered as unknown. By collecting both maternal report and data from Statistics Norway, categories of paternal identity may overlap largely with paternal origin (Norwegian-born, foreign-born, or unregistered), but they will still be different in content and therefore analyzed separately. The MBRN also included data on paternal age.

Paternal and maternal region of birth

Paternal and maternal country of birth were categorized into the following regions according to the classification of Global Burden of Disease (GBD) [26]: high-income countries; Central and Eastern Europe, Central Asia; North Africa and the Middle East; sub-Saharan Africa; South Asia; Southeast Asia, East Asia, and Oceania; and Latin America and the Caribbean.

Maternal factors

The MBRN provided data on maternal age, marital status (single, married/cohabiting, divorced/separated/widowed, other/not given), and parity (0, 1, 2, 3, or ≥4 previous births). Statistics Norway provided data on maternal level of education (no education, primary school, secondary school, university/college, missing) and mother’s gross income (categorized into quartiles, missing).

Adverse neonatal outcomes

The main outcomes were very preterm birth, moderately preterm birth, SGA, low Apgar score, and stillbirth. Gestational age was based on ultrasound estimation or, when such information was lacking, calculated from the first day of the last menstrual period. In the analyses of very preterm birth (22+0–31+6 gestational weeks) and moderately preterm birth (32+0–36+6 gestational weeks), term birth, including post-term birth (≥37+0 gestational weeks), was used as the comparison group. In analyses of very preterm birth, moderately preterm births were excluded, and in analysis of moderately preterm birth, very preterm births were excluded. For calculating SGA, we used Norwegian standards combining information on gestational age, birthweight, and sex of the child [27]. In the analyses of SGA, we excluded births with missing data on any of those 3 variables. Low Apgar score was defined as <7 at 5 minutes, which is commonly used and regarded as clinically relevant [28,29]. Stillbirth was defined as a pregnancy loss at ≥22 weeks of gestation (or with a birthweight ≥500 g if data on gestational age were missing).

Statistical methods

To examine the associations between paternal origin and neonatal outcomes, we estimated odds ratios (ORs) with 95% confidence intervals (CIs) using binary logistic regression models. Adjustments were made for year of birth, parity, maternal age, paternal age, marital status, maternal education, and mother’s gross income. To account for nonlinear relations, year of birth, maternal age, and paternal age were incorporated as polynomial quadratic model terms. To account for dependency between births by the same mother, we used robust standard errors that allowed for within-mother clustering.

To avoid listwise deletion and potential bias due to missing data in the covariates education and income, we performed multiple imputations on missing data, assuming that the missing data could be explained by other variables in the data set (missing at random). The imputation algorithm used was multivariate normal [30], and a total of 5 imputed data sets were created. Separate imputation models were used for each outcome and included the 4 respective outcomes, maternal country of birth, and exposure variables (paternal origin and paternal identity), as well as all adjustment variables included in the final analytical models.

An a priori strategy of analyzing data separately for primiparous and multiparous women was initially chosen, based on the fact that primiparous and multiparous women are often provided with different recommendations in antenatal guidelines [31]. Therefore, we believed that this difference could affect associations differently for these groups. Because there was no strong indication that the associations did differ between these groups in relation to paternal origin, we reanalyzed the data and report the associations for primiparous and multiparous women combined.

All analyses were performed using Stata IC version 16 (Stata Statistical Software, College Station, TX, USA) for Windows.

Ethics

The Regional Committees for Medical and Health Research Ethics approved this study, reference number: 2014/1278/REK South-East, Norway. A pseudonymous identity number was generated for each individual in the data set prior to access by the authors.

Results

The final sample included births to migrant (n = 240,759) and Norwegian-born (n = 1,232,327) women giving birth in Norway between the years 1990 and 2016. The women and men originated from 202 and 203 different countries, respectively, including Norway. In births to migrant women, the 10 most common paternal countries of birth were Norway (28.9%), Somalia (5.4%), Pakistan (5.1%), Iraq (4.6%), Poland (4.5%), Vietnam (3.0%), Sri Lanka (2.7%), Turkey (2.5%), Kosovo (2.4%), and Lithuania (2.0%). Similar, the 10 most common maternal countries of birth were Somalia (6.8%), Poland (6.4%), Sweden (6.3%), Pakistan (6.1%), Iraq (4.6%), the Philippines (4.0%), Vietnam (3.7%), Thailand (3.3%), Russia (2.9%), and Turkey (2.8%). In births to Norwegian-born women, the 10 most common paternal countries of birth were Norway (92.2%), Sweden (1.0%), United Kingdom (0.6%), Denmark (0.5%), the United States of America (0.5%), Germany (0.3%), Turkey (0.2%), the Netherlands (0.2%), Chile (0.1%), and Iran (0.1%).

Table 1 shows the background characteristics of the sample of births to migrant and Norwegian-born women by paternal origin (Norwegian-born, foreign-born, and unregistered). In births to migrant women and Norwegian-born fathers (29%), the women most commonly originated from high-income countries or from Southeast Asia, East Asia, or Oceania; a majority of the mothers were married or cohabiting, had a high level of education, and belonged to the highest maternal gross income categories, and almost half of the women were primiparous. In births to migrant women and foreign-born fathers (63%), both parents mostly originated from Central and Eastern Europe and Central Asia or North Africa and the Middle East; a majority of women were married or cohabiting and had low levels of education (or missing information) and maternal gross income, and 39% were primiparous. When paternal origin was unregistered (8%), paternal age and paternal identity was also missing for 29% and 9% of the births, respectively; the mothers commonly originated from sub-Saharan Africa or Central and Eastern Europe and Central Asia, many were single and had low levels of education (or missing information) and maternal gross income, and 26% were primiparous.

Table 1

Background characteristics by paternal origin in births to migrant (n = 240,759) and Norwegian-born (n = 1,232,327) women in Norway (1990–2016).

	Migrant Women				Norwegian-Born Women
	Paternal Origin
	Norwegian-born	Foreign-born	Unregistered		Norwegian-born	Foreign-born	Unregistered
	n (%)	n (%)	n (%)	P-value	n (%)	n (%)	n (%)	P-value
Total	69,477 (28.9)	152,097 (63.2)	19,185 (8.0)		1,135,712 (92.2)	73,763 (6.0)	22,852 (1.9)
Paternal factors
Paternal age, years (mean ± SD)	35.7 ± 7.6	33.7 ± 6.5	36.4 ± 8.2		31.6 ± 5.8	32.7 ± 6.2	34.0 ± 6.6
Paternal age, missing	91 (0.1)	429 (0.3)	5,615 (29.3)		1,293 (0.1)	234 (0.3)	7,498 (32.9)
Paternal origin (GBD)				<0.001				<0.001
High-income countries	69,477 (100.0)	19,454 (12.8)			1,135,712 (100.0)	50,423 (68.4)
Central and Eastern Europe, Central Asia		36,648 (24.1)				4,270 (5.8)
North Africa, Middle East		35,594 (23.4)				7,353 (10.0)
Sub-Saharan Africa		24,064 (15.8)				4,599 (6.2)
Southeast Asia, East Asia, Oceania		19,053 (12.5)				2,383 (3.2)
South Asia		16,175 (10.6)				1,449 (2.0)
Latin America, the Caribbean		1,109 (0.7)				3,274 (4.4)
Paternal identity unknownǂ	70 (0.1)	220 (0.1)	1,798 (9.4)	<0.001	1,171 (0.1)	131 (0.2)	4,857 (21.3)	<0.001
Maternal factors
Maternal age, years (mean ± SD)	30.5 ± 5.0	29.2 ± 5.2	30.3 ± 5.9		28.9 ± 5.1	30.2 ± 5.3	30.4 ± 6.3
Marital status				<0.001				<0.001
Single	2,035 (2.9)	6,163 (4.1)	4,452 (23.2)		67,517 (5.9)	7,016 (9.5)	8,486 (37.1)
Married	47,842 (68.9)	124,274 (81.7)	10,522 (54.8)		505,758 (44.5)	36,758 (49.8)	6,222 (27.2)
Cohabiting	18,422 (26.5)	17,523 (11.5)	2,919 (15.2)		549,542 (48.4)	28,548 (38.7)	7,402 (32.4)
Divorced/separated/widowed	510 (0.7)	1,958 (1.3)	786 (4.1)		4,317 (0.4)	738 (1.0)	400 (1.8)
Other/not given	668 (1.0)	2,179 (1.4)	506 (2.6)		8,578 (0.8)	703 (1.0)	342 (1.5)
Maternal origin (GBD)				<0.001				<0.001
High-income countries	31,350 (45.1)	17,890 (11.8)	2,282 (11.9)		1,135,712 (100.0)	73,763 (100.0)	22,852 (100.0)
Central and Eastern Europe, Central Asia	12,120 (17.4)	39,066 (25.7)	4,113 (21.4)
North Africa, Middle East	2,094 (3.0)	34,108 (22.4)	2,001 (10.4)
Sub-Saharan Africa	2,317 (3.3)	23,544 (15.5)	5,930 (30.9)
Southeast Asia, East Asia, Oceania	14,931 (21.5)	20,094 (13.2)	3,537 (18.4)
South Asia	2,495 (3.6)	16,052 (10.6)	533 (2.8)
Latin America, the Caribbean	4,170 (6.0)	1,343 (0.9)	789 (4.1)
Maternal education§				<0.001				<0.001
No education	420 (0.7)	3,908 (3.6)	774 (5.7)		36 (0.0)	3 (0.0)	3 (0.0)
Primary education	10,615 (18.6)	37,872 (35.2)	6,205 (46.0)		236,069 (20.8)	13,832 (18.8)	7,375 (32.6)
Secondary school	14,509 (25.4)	28,650 (26.6)	3,231 (24.0)		429,431 (37.9)	22,266 (30.3)	7,669 (33.9)
University/college	31,603 (55.3)	37,256 (34.6)	3,283 (24.3)		468,317 (41.3)	37,423 (50.9)	7,582 (33.5)
Maternal education, missing	12,330 (17.8)	44,411 (29.2)	5,692 (29.7)		1,859 (0.2)	239 (0.3)	223 (1.0)
Mother's gross income§				<0.001				<0.001
≤25th percentile	14,221 (25.8)	34,053 (35.7)	5,271 (44.5)		255,270 (24.3)	13,218 (19.7)	5,195 (27.0)
25th–50th percentile	10,398 (18.9)	17,524 (18.4)	2,042 (17.2)		276,078 (26.2)	13,842 (20.6)	3,942 (20.5)
50th–75th percentile	13,541 (24.6)	21,953 (23.0)	2,417 (20.4)		266,901 (25.4)	17,202 (25.6)	4,321 (22.5)
≥75th percentile	16,886 (30.7)	21,857 (22.9)	2,114 (17.9)		254,270 (24.2)	22,951 (34.2)	5,790 (30.1)
Mother’s gross income, missing	14,431 (20.8)	56,710 (37.3)	7,341 (38.3)		83,193 (7.3)	6,550 (8.9)	3,604 (15.8)
Parity				<0.001				<0.001
0	34,684 (49.9)	59,294 (39.0)	4,919 (25.6)		467,831 (41.2)	33,359 (45.2)	8,126 (35.6)
1	23,784 (34.2)	48,826 (32.1)	7,522 (39.2)		416,257 (36.7)	26,086 (35.4)	5,169 (22.6)
2	8,245 (11.9)	24,440 (16.1)	3,604 (18.8)		188,511 (16.6)	10,490 (14.2)	5,228 (22.9)
3	1,983 (2.9)	10,611 (7.0)	1,814 (9.5)		46,399 (4.1)	2,708 (3.7)	3,020 (13.2)
≥4	781 (1.1)	8,926 (5.9)	1,326 (6.9)		16,714 (1.5)	1,120 (1.5)	1,309 (5.7)

Abbreviations: GBD, Global Burden of Disease; SD, standard deviation.

ǂA known father may be either foreign-born or Norwegian-born.

§Percentages are calculated from nonmissing data.

In births to Norwegian-born women and Norwegian-born fathers (92%), the mothers often had high levels of education and maternal gross income. In births to Norwegian-born women and foreign-born fathers (6%), the fathers commonly originated from high-income countries and North Africa and the Middle East, and the mothers had high levels of education and maternal gross income. If paternal origin was unregistered (2%), paternal age was often missing, paternal identity was often unknown, and the mothers often had low levels of education, had missing data on maternal gross income, and had high parity.

Fig 2 shows paternal origin (Norwegian-born, foreign-born, or unregistered) in relation to maternal region of birth. In births to migrant women, a Norwegian-born father was common among women from high-income countries; Southeast Asia, East Asia, and Oceania; and Latin America and the Caribbean, and a foreign-born father was common among women from North Africa and the Middle East and South Asia as well as in women from sub-Saharan Africa. Unregistered paternal origin was common in births to migrant women from sub-Saharan Africa (19%); Latin America and the Caribbean (13%); Southeast Asia, East Asia, and Oceania (9%); and Central and Eastern Europe and Central Asia (7%). In births to Norwegian-born women, paternal origin was registered as Norwegian-born and foreign-born in 92% and 6%, respectively. Paternal origin was unregistered in 2% of births to Norwegian-born women.

Fig 2

Proportion of births to migrant and Norwegian-born women giving birth in Norway (1990–2016) by maternal region of birth (GBD categories; Norwegian-born women in a separate category) and paternal origin (Norwegian-born, foreign-born, and unregistered).

GBD, Global Burden of Disease.

Table 2 shows the associations between paternal origin and adverse neonatal outcomes in births to migrant women. Overall, the results only changed slightly after adjustments for year of birth, parity, maternal age, paternal age, marital status, maternal education, and mother’s gross income. In births to migrant women, a foreign-born father was associated with increased odds of very preterm birth (adjusted OR [aOR] 1.20; CI 1.08–1.33), SGA (aOR 1.48; CI 1.43–1.53), low Apgar score (aOR 1.14; CI 1.05–1.23), and stillbirth (aOR 1.26; CI 1.08–1.48) compared with a Norwegian-born father. In births for which paternal origin was unregistered, the odds were increased for very preterm birth (aOR 2.29; CI 1.97–2.66), moderately preterm birth (aOR 1.15; CI 1.06–1.25), SGA (aOR 1.50; CI 1.42–1.58), low Apgar score (aOR 2.23; CI 1.99–2.50), and stillbirth (aOR 4.87; CI 3.98–5.96) compared with births with a Norwegian-born father.

Table 2

Associations between paternal origin and adverse neonatal outcomes in births to migrant women in Norway (1990–2016).

	Very Preterm (22+0–31+6 gwks)†	Moderately Preterm (32+0–36+6 gwks)ǂ	SGA§	Apgar Score <7 at 5 Minutes$	Stillbirth
Paternal origin
Norwegian-born (n)	64,818	67,369	67,925	69,246	69,477
No cases (%)	615 (0.9)	3,166 (4.7)	6,466 (9.5)	1,043 (1.5)	229 (0.3)
Reference	1.00	1.00	1.00	1.00	1.00
Foreign-born (n)	141,697	146,911	148,350	151,538	152,097
No cases (%)	1,573 (1.1)	6,787 (4.6)	19,836 (13.4)	2,606 (1.7)	695 (0.5)
OR (95% CI)	1.17 (1.06–1.29)	0.98 (0.94–1.03)	1.47 (1.42–1.52)	1.14 (1.06–1.23)	1.39 (1.19–1.61)
P-value	0.001	0.443	<0.001	<0.001	<0.001
aOR (95% CI)¶	1.20 (1.08–1.33)	0.98 (0.93–1.03)	1.48 (1.43–1.53)	1.14 (1.05–1.23)	1.26 (1.08–1.48)
P-value	0.001	0.330	<0.001	0.001	0.004
Unregistered (n)	17,656	18,285	18,634	19,062	19,185
No cases (%)	386 (2.2)	1,015 (5.6)	2,420 (13.0)	644 (3.4)	294 (1.5)
OR (95% CI)	2.33 (2.05–2.66)	1.19 (1.11–1.28)	1.42 (1.35–1.49)	2.29 (2.07–2.53)	4.71 (3.96–5.59)
P-value	<0.001	<0.001	<0.001	<0.001	<0.001
aOR (95% CI)¶	2.29 (1.97–2.66)	1.15 (1.06–1.25)	1.50 (1.42–1.58)	2.23 (1.99–2.50)	4.87 (3.98–5.96)
P-value	<0.001	0.001	<0.001	<0.001	<0.001

Abbreviations: aOR, adjusted OR; CI, confidence interval; gwk, gestational week; OR, odds ratio; SGA, small for gestational age.

†Cases with missing data on gestational age (n = 5,620) and moderately preterm births (n = 10,968) excluded.

ǂCases with missing data on gestational age (n = 5,620) and very preterm births (n = 2,574) excluded.

§Cases with missing data on SGA excluded (n = 5,850).

$Cases with missing data on Apgar score excluded (n = 913).

¶Adjusted for year of birth, parity, maternal age, paternal age, marital status, maternal education, and mother’s gross income.

Table 3 shows the associations between paternal origin and adverse neonatal outcomes in births to Norwegian-born women. In births to Norwegian-born women, a foreign-born father was associated with increased odds of SGA (aOR 1.13; CI 1.09–1.16) and decreased odds of moderately preterm birth (aOR 0.95; CI 0.91–0.99) compared with a Norwegian-born father. In births for which paternal origin was unregistered, the odds were increased for very preterm birth (aOR 4.39; CI 4.05–4.76), moderately preterm birth (aOR 1.62; CI 1.53–1.71), SGA (aOR 1.30; CI 1.24–1.36), low Apgar score (aOR 3.51; CI 3.26–3.78), and stillbirth (aOR 9.00; CI 8.15–9.93) compared with births with a Norwegian-born father.

Table 3

Associations between paternal origin and adverse neonatal outcomes in births to Norwegian-born women in Norway (1990–2016).

	Very Preterm (22+0–31+6 gwks)†	Moderately Preterm (32+0–36+6 gwks)ǂ	SGA§	Apgar Score <7 at 5 Minutes$	Stillbirth
Paternal origin
Norwegian-born (n)	1,045,115	1,083,099	1,092,170	1,129,567	1,135,712
No cases (%)	10,025 (1.0)	48,009 (4.4)	88,693 (8.1)	14,714 (1.3)	4,356 (0.4)
Reference	1.00	1.00	1.00	1.00	1.00
Foreign-born (n)	68,475	70,854	71,470	73,416	73,763
No cases (%)	674 (1.0)	3,053 (4.3)	6,628 (9.3)	995 (1.4)	281 (0.4)
OR (95% CI)	1.03 (0.95–1.11)	0.97 (0.93–1.01)	1.16 (1.12–1.19)	1.04 (0.98–1.11)	0.99 (0.88–1.12)
P-value	0.527	0.140	<0.001	0.226	0.912
aOR (95% CI)¶	1.03 (0.95–1.12)	0.95 (0.91–0.99)	1.13 (1.09–1.16)	0.98 (0.91–1.04)	1.03 (0.91–1.16)
P-value	0.504	0.015	<0.001	0.466	0.687
Unregistered (n)	20,180	20,883	21,724	22,485	22,852
No cases (%)	926 (4.6)	1,629 (7.8)	2,483 (11.4)	1,034 (4.6)	739 (3.2)
OR (95% CI)	4.97 (4.63–5.32)	1.82 (1.73–1.92)	1.46 (1.40–1.52)	3.65 (3.42–3.90)	8.68 (8.00–9.41)
P-value	<0.001	<0.001	<0.001	<0.001	<0.001
aOR (95% CI)¶	4.39 (4.05–4.76)	1.62 (1.53–1.71)	1.30 (1.24–1.36)	3.51 (3.26–3.78)	9.00 (8.15–9.93)
P-value	<0.001	<0.001	<0.001	<0.001	<0.001

Abbreviations: aOR, adjusted OR; CI, confidence interval; gwk, gestational week; OR, odds ratio; SGA, small for gestational age.

†Cases with missing data on gestational age (n = 45,866) and moderately preterm births (n = 52,691) excluded.

ǂCases with missing data on gestational age (n = 45,866) and very preterm births (n = 11,625) excluded.

§Cases with missing data on SGA excluded (n = 46,963).

$Cases with missing data on Apgar score excluded (n = 6,859).

¶Adjusted for year of birth, parity, maternal age, paternal age, marital status, maternal education, and mother’s gross income.

In births to migrant women, unknown paternal identity was associated with increased odds of very preterm birth (aOR 10.36; CI 8.04–13.36), moderately preterm birth (aOR 1.26; CI 1.03–1.54), SGA (aOR 1.35; CI 1.18–1.54), low Apgar score (aOR 3.26; CI 2.61–4.06), and stillbirth (aOR 16.62; CI 13.62–20.28) compared with known paternal identity (S1 Table). In births to Norwegian-born women, unknown paternal identity was associated with increased odds of very preterm birth (aOR 15.43; CI 13.63–17.46), moderately preterm birth (aOR 1.58; CI 1.42–1.75), SGA (aOR 1.49; CI 1.38–1.60), low Apgar score (aOR 5.77; CI 5.09–6.55), and stillbirth (aOR 28.52; CI 25.83–31.49) compared with known paternal identity (S1 Table).

Discussion

Our hypothesis that a foreign-born father of the child would be associated with an increased risk of adverse pregnancy outcomes in births to migrant women was confirmed. In births to migrant women, a foreign-born father was associated with increased odds of very preterm birth, SGA, low Apgar score, and stillbirth compared with a Norwegian-born father. Unregistered paternal country of origin was associated with increased odds of all adverse outcomes investigated in migrant women (very preterm birth, moderately preterm birth, SGA, low Apgar score, and stillbirth) compared with a Norwegian-born father. In births to Norwegian-born women, a foreign-born father was associated with increased odds of SGA and decreased odds of moderately preterm birth when compared with a Norwegian-born father. However, unregistered paternal origin also increased the odds of all adverse outcomes in this group of women.

The main strengths of this study include the standardized collection of paternal, maternal, and infant data [17,18] in a population including nearly all births to migrant women in Norway over a period of 26 years. Limitations include lack of data on previous preterm births, which is a known predictor for recurrent preterm delivery [32]. Furthermore, although lifestyle factors may be implicated in adverse outcomes, access to such information was limited in the current study. On the other hand, because many migrant women in high-income countries appear to have some healthier lifestyle habits than women born in these countries, such as less use of alcohol and tobacco [33,34], adverse outcomes for migrant women may be less likely to be attributable to these factors. Unfortunately, we did not have access to information on paternal education or income. Additional information on paternal education may have explained some of the increased risk because such information is acknowledged to be an independent risk factor for certain adverse neonatal outcomes such as preterm birth [35,36]. To better understand the impact of socioeconomic factors, we did, however, make adjustments for maternal education and mother’s gross income. Recommendations for future research include investigating the impact of a wider range of paternal factors in a larger sample, perhaps by linking data from all Nordic countries [37]. A larger sample would further allow for investigating possible interactions between paternal and maternal origin.

A foreign-born father was associated with increased odds of very preterm birth, SGA, stillbirth, and low Apgar score at 5 minutes in births to migrant women. Our results related to very preterm birth support previous findings from 1 Swedish [9] and 1 Canadian [10] study, the increased odds of SGA is consistent with findings from 1 Swedish study [3], and the increased odds of stillbirth is consistent with findings from 1 Canadian [8] and 1 Australian study [11]. In addition, 1 Swedish study reports an increased risk of low Apgar score in migrant women, irrespective of paternal origin [3]. The slightly lower odds found for moderately preterm birth associated with a foreign-born father compared with a Norwegian-born father is consistent with findings from 1 Canadian study [10] and 1 Swedish study [9]. Both studies report that such findings do not apply to all migrant women, highlighting the importance of being careful with generalization of migrant women’s health and individual needs in maternity care. Being able to identify women at risk of adverse neonatal outcomes and then attend to such risks is clinically very important. Very preterm birth is associated with high-cost neonatal intensive care and long-term complex health needs affecting the infant and the whole family [38]; SGA may reflect a range of maternal or infant health problems in need of medical attention [4,39]; stillbirth is associated with high emotional and economic costs affecting the family, communities, and society [40]; and low Apgar score is associated with infant mortality and morbidity [41].

A partner from the host population might ease the integration process by providing the woman with increased wealth and social capital less likely to be available to couples in which both parents are foreign-born [3,11]. He may further facilitate communication between the woman and caregivers and better guide her through the healthcare system [6,11,42]. It is also possible that a migrant woman may be less prone to experience discrimination or disrespectful care from caregivers [43] if the father is from the host population. Such experiences in the receiving country may be important in maintaining “the healthy migrant effect,” i.e., that many migrants are of good health, sometimes even better health than the host population [33]. Alternatively, the positive impact of a Norwegian-born father may be explained by maternal factors, rather than paternal ones. In our study, only a few women from the GBD region North Africa and the Middle East reported a Norwegian-born father of the child, whereas a partner from the host population was more common among women from the following regions: high-income countries and Southeast Asia, East Asia, and Oceania. Women from high-income countries are less likely to experience adverse neonatal outcomes compared with more vulnerable groups of migrant women, such as refugees [44]. However, the protective influence of a Norwegian-born partner may not apply to all migrant women. Some migrant women who marry men from the host population have been found to be vulnerable to exploitation, social isolation, and spousal violence [45], factors that may influence a pregnancy outcome negatively [7,46,47].

In births to Norwegian-born women, a foreign-born father was not associated with increased odds of adverse outcomes other than SGA when compared with a Norwegian-born father. These results are difficult to interpret because SGA does not differentiate between growth-restricted babies and healthy babies who are small because of genetic factors [4,39,48]. Thus, biological variation may explain the increased odds of SGA associated with a migrant parent rather than maternal or infant health problems (e.g., malformations or placental insufficiency) [4,39,48]. Further, maternal factors may explain why we found no increased odds of adverse outcomes other than SGA in births to Norwegian-born women. Unfortunately, the present study did not allow for analyses stratified by maternal origin because of the limited number of adverse cases in each subgroup of migrant women. It is worth noting that when Norwegian-born women’s babies had foreign-born fathers, these fathers were more likely to come from other high-income countries with fewer cultural and language barriers [49], particularly another Scandinavian country or an English-speaking country, compared with fathers of babies with migrant mothers.

Our findings related to unregistered paternal origin are in line with previous research from the US, Canada, and Australia, where missing paternal demographics have been associated with adverse outcomes such as preterm birth, low birthweight, low Apgar score, stillbirth, and neonatal death [12-14]. However, none of the studies were specific to migrant women [12-14], and the US study only included twin births [12]. Thus, the current study adds important information relevant when planning care for migrant women in particular. Paternal origin was unregistered in as many as 1 in 5 births to women originating from sub-Saharan Africa. It is possible that a lack of information about fathers of the babies of sub-Saharan African women and their poorer outcomes might be explained by more limited health literacy [50], distrust in the healthcare system [51,52], or a delay in seeking antenatal care [52-54]. This might also be the case for other migrant women, such as those who have fled from wars and conflicts [44]. For migrants in general, data registration is likely to be hampered by language and communication difficulties [55]. Notably, other studies have excluded individuals for whom paternal country of birth [8-10], race, or ethnicity were missing [56], which seems problematic given our results. Our findings suggest that identifying women for whom paternal demographics are missing may help identify high-risk women in maternity care and should therefore alert clinicians.

Unknown paternal identity was particularly strongly associated with very preterm birth and stillbirth. Women may withhold information on a child’s biological father for a variety of reasons, including lack of knowledge about the father, economic reasons, or intentions to protect the child, themselves, or others from potential shame or threats [57]. However, these results should be interpreted with caution because the variable paternal identity obtained from the MBRN has not been investigated previously in relation to adverse neonatal outcomes in migrant women. We were unable to differentiate between births in which paternal identity was unknown to the mother or intentionally not reported by the mother or caregiver or if such information was missing because of poor registration routines. We cannot exclude the possibility that the associations between paternal identity and adverse neonatal outcomes are biased for reasons such as systematic under-reporting for women with adverse neonatal outcomes, particularly when a baby is born premature or stillborn. Given the severity of the findings, further studies on unknown paternal identity in the register are warranted.

In conclusion, we found that a foreign-born father was associated with adverse neonatal outcomes among births to migrant women, but to a lesser degree among births to nonmigrant women, when compared with a Norwegian-born father. Unregistered paternal origin was associated with higher odds of adverse neonatal outcomes in births to both migrant and nonmigrant women when compared with Norwegian-born fathers. Increased attention to paternal origin may help identify women in maternity care at risk for adverse neonatal outcomes.

STROBE, Strengthening the Reporting of Observational Studies in Epidemiology

(DOCX)

Click here for additional data file.

Associations between paternal identity and adverse neonatal outcomes in births to migrant and Norwegian-born women in Norway (1990–2016).

(DOCX)

Click here for additional data file.

11 May 2020

Dear Dr Vik,

Thank you for submitting your manuscript entitled "Associations between paternal origin and adverse neonatal outcomes in births to migrant women: a Norwegian population-based study" for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff as well as by an academic editor with relevant expertise and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript within two working days, i.e. by .

Login to Editorial Manager here: https://www.editorialmanager.com/pmedicine

Once your full submission is complete, your paper will undergo a series of checks in preparation for peer review. Once your manuscript has passed all checks it will be sent out for review.

Feel free to email us at plosmedicine@plos.org if you have any queries relating to your submission.

Kind regards,

Artur Arikainen,

Associate Editor

PLOS Medicine

11 Jun 2020

Dear Dr. Vik,

Thank you very much for submitting your manuscript "Associations between paternal origin and adverse neonatal outcomes in births to migrant women: a Norwegian population-based study" (PMEDICINE-D-20-01868R1) for consideration at PLOS Medicine.

Your paper was evaluated by a senior editor and discussed among all the editors here. It was also discussed with an academic editor with relevant expertise, and sent to independent reviewers, including a statistical reviewer. The reviews are appended at the bottom of this email and any accompanying reviewer attachments can be seen via the link below:

[LINK]

In light of these reviews, I am afraid that we will not be able to accept the manuscript for publication in the journal in its current form, but we would like to consider a revised version that addresses the reviewers' and editors' comments. Obviously we cannot make any decision about publication until we have seen the revised manuscript and your response, and we plan to seek re-review by one or more of the reviewers.

In revising the manuscript for further consideration, your revisions should address the specific points made by each reviewer and the editors. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments, the changes you have made in the manuscript, and include either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please submit a clean version of the paper as the main article file; a version with changes marked should be uploaded as a marked up manuscript.

In addition, we request that you upload any figures associated with your paper as individual TIF or EPS files with 300dpi resolution at resubmission; please read our figure guidelines for more information on our requirements: http://journals.plos.org/plosmedicine/s/figures. While revising your submission, please upload your figure files to the PACE digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at PLOSMedicine@plos.org.

We expect to receive your revised manuscript by Jul 02 2020 11:59PM. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. If new competing interests are declared later in the revision process, this may also hold up the submission. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

Please use the following link to submit the revised manuscript:

https://www.editorialmanager.com/pmedicine/

Your article can be found in the "Submissions Needing Revision" folder.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see http://journals.plos.org/plosmedicine/s/submission-guidelines#loc-methods.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

We look forward to receiving your revised manuscript.

Sincerely,

Artur Arikainen,

Associate Editor

PLOS Medicine

plosmedicine.org

-----------------------------------------------------------

Requests from the editors:

1. Please address all of the reviewers’ comments below.

2. Abstract:

a. Please combine the Methods and Findings sections into one section, “Methods and findings”.

b. Please include basic demographic information for the participants (age etc.).

c. In the last sentence of the Abstract Methods and Findings section, please describe the main limitation(s) of the study's methodology.

d. Please quantify the main results (with 95% CIs and p values).

3. The Data Availability Statement (DAS) requires revision. For each data source used in your study:

a. If the data are freely or publicly available, note this and state the location of the data: within the paper, in Supporting Information files, or in a public repository (include the DOI or accession number).

b. If the data are owned by a third party but freely available upon request, please note this and state the owner of the data set and contact information for data requests (web or email address). Note that a study author cannot be the contact person for the data.

c. If the data are not freely available, please describe briefly the ethical, legal, or contractual restriction that prevents you from sharing it. Please also include an appropriate contact (web or email address) for inquiries (again, this cannot be a study author).

4. At this stage, we ask that you include a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract. Please see our author guidelines for more information: https://journals.plos.org/plosmedicine/s/revising-your-manuscript#loc-author-summary

5. Please use the "Vancouver" style for reference formatting, and see our website for other reference guidelines https://journals.plos.org/plosmedicine/s/submission-guidelines#loc-references. Citations should be in square brackets, and preceding punctuation.

6. Methods:

a. Please give exact date ranges for patient recruitment.

b. Please confirm whether the patient data were fully anonymised prior to access by the authors, or whether patients provided written informed consent for the use of their data in research.

7. Results:

a. Please quantify all results with 95% CIs and p values.

b. Table 1: Please define ‘GBD’ in the legend.

c. Tables 2 and 3: Please define ‘gwks’ in the legend.

8. Discussion: Please include a clear paragraph (or more) on the strengths and limitations of the study.

9. Line 236: Please replace “significant” with “notable” or similar.

10. Please provide access information (URL, DOI, and/or volume/issue/page) for all references, eg. no 2, 22, 41.

11. Please ensure that the study is reported according to the STROBE guidelines, and include the completed STROBE checklist as Supporting Information. 1 Please add the following statement, or similar, to the Methods: "This study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline (S1 Checklist)."

The STROBE guideline can be found here: http://www.equator-network.org/reporting-guidelines/strobe/ When completing the checklist, please use section and paragraph numbers, rather than page numbers.

12. Did your study have a prospective protocol or analysis plan? Please state this (either way) early in the Methods section.

a. If a prospective analysis plan (from your funding proposal, IRB or other ethics committee submission, study protocol, or other planning document written before analyzing the data) was used in designing the study, please include the relevant prospectively written document with your revised manuscript as a Supporting Information file to be published alongside your study, and cite it in the Methods section. A legend for this file should be included at the end of your manuscript.

b. If no such document exists, please make sure that the Methods section transparently describes when analyses were planned, and when/why any data-driven changes to analyses took place.

c. In either case, changes in the analysis-- including those made in response to peer review comments-- should be identified as such in the Methods section of the paper, with rationale.

---------

Comments from the reviewers:

Reviewer #1: I confine my remarks to statistical aspects of this paper. Unfortunately, I think there are some fairly serious issues to resolve.

First, the authors should not use causal language (e.g. line 49 "influence" but other places too). This is an observational study, causation cannot be inferred.

Second, the dependent variable for gestation should be gestation time in days or weeks and a spline can be used to evaluate nonlinearity. But, if only the categorized data is available, then ordinal logistic regression should be used. Similarly, Apgar score should not be categorized. Doing so makes an Apgar of 1 the same as one of 6 and a score of 7 the same as 10. That makes no sense.

Third, independent variables should also not be categorized. In *Regression Modelling Strategies* Frank Harrell lists 11 problems with this and sums up "nothing could be more disastrous". Leave age and length of residence in years.

Fourth, for maternal and paternal origin, the reference group should be Norwegian. First, this is both the largest group and the "norm". Second, using foreign born as the reference puts the other two levels below and above the reference. It is better to have the lowest (or highest) category as the reference.

Peter Flom

Reviewer #2: The manuscript entitled "Associations between paternal origin and adverse neonatal outcomes in births to migrant women: a Norwegian population-based study" is an interesting study to provide insight into the effect of paternal origin and the risk of adverse pregnancy outcomes among migrant woman. However, despite the interesting results, I have some comments on the methodology and the discussion that need to be clarified.

General comments

The association between missing information and adverse health outcomes (and pregnancy outcomes in particular) has been described previously in many studies. The authors should include a wider description and discussion of the unknown paternal identity and unregistered paternal origin to ensure that readers understand exactly what the researchers studied. The difference between unknown paternal identity, unregistered paternal origin and single mother need to be discussed. That is one of the main focus of the paper, but the authors should clarify the social, health and clinical aspects behind those variables: single mother? not access to social and health rights? …. The unreported father is a proxy for more noteworthy factors.

Some methodological details should be expanded and clarified.

- I was wondering if the missing data were MNAR (Missing not at random) . Did you check if there were associated to adverse outcome? We know that missing data for sociodemographic data are more important among stillbirths. If the data are MNAR, the multiple imputation is more complex, and some assumptions need to be verified (check with a statistician)

- For the logistic regression, did you check the Goodness of fit of the models and interaction tests?

- The stratification primiparous/multiparous need to be discussed because the profiles are similar. The interaction test could justify the choice of stratification rather than adjustment for parity.

- Maternal factors as single mother and maternal length of residence are mentioned in the methodology but not analyzed? Why ?

Weakness of the discussion

The authors should include more information in the discussion part to clarify some points to avoid confusion.

- This study requires a comparison with the non-migrant population. The unknown paternal identity and unregistered paternal origin is probably also associated to increased OR for adverse outcome among non-migrant population. The results do not fully support a conclusion specific to migrant population.

- P16 line 267: the discussion for sub-Saharan Africa women can be generalized for other migrant group (literacy, distrust healthcare system, delay antenatal care,..) because it is not specific to sub-saharan Africa mother. Other studies have shown the high proportion of single mother among sub-Saharan African mother.

The manuscript is certainly well written and attractive, but the results do not provide a substantial advance over existing knowledge for Plos Medicine. The interpretation of the results needs a wider discussion for their implication to clinicians and policy makers.

Reviewer #3: This manuscript covers the important issue of paternal origin and migrant primip and multip mothers in conjunction with prematurity, low Apgar score, and stillbirth in Norway. The results when controlling for maternal factors of age, education, and income are not surprising, mothers with foreign-born fathers had a higher risk of very preterm and stillbirth compared with Norwegian-born fathers (regardless of multip or primip mothers). Paternal foreign-born status was also associated with lower Apgar score compared to Norwegian-born fathers. Additionally, unknown paternal origin was linked to higher risk of all adverse birth outcomes for both primip and multip mothers. Finally, also expected, unknown father identity was associated with adverse birth outcomes compared with identified father, regardless of primip or multip mother.

The dearth of research on the impact of fathers on birth outcomes makes this a very important contribution to the literature. Furthermore, given the disparity in prenatal care given as noted in the Methods section, hopefully this further highlights the existing inequity and empowers policy makers and providers to move toward solutions in Norway and beyond.

There are several major issues that do need to be addressed including why the models did not adjust for any paternal factors, why small for gestational age was not included as an outcome, and why the authors excluded the Norwegian born mothers rather than using them in a comparison with migrant mothers.

Major issues (although the authors may not be able to do all the analyses mentioned, it would be helpful to 1. Add analyses, 2. Add to a limitation, or 3. Note this is a future direction of the research team):

1. The authors note they do not have access to paternal education which does have an independent effect on birth outcomes. Yet they have paternal age and do not adjust for this factor also known to be associated with birth outcomes, especially stillbirth.

2. Further unlike advanced maternal age which is typically defined as 35 years, advanced paternal age is typically defined at 40. It may be beneficial to add this as a category and further examine this in conjunction with migrant mothers and paternal foreign-born status. Also why no assessment of teen aged parents either mother or father (less than 20?), as these lower extremes of ages have also been associated with poor birth outcomes.

3. It is unclear why small for gestational age (a birth outcome previously having been associated with fathers and stress) was not assessed. Could this be added?

4. Another interesting outcome that should be considered if available is NICU admission. NICU admission is more impactful than low apgar score which is not clearly associated with nor predictive of poor neonatal outcomes.

5. It was also unclear why the authors excluded the Norwegian born mothers. Couldn't this group be assessed for paternal foreign born or not and the outcomes could be instructive in relation to migrant mothers and paternal foreign born status. Additionally, outcomes for the general population as a benchmark would also be important to know for generalizability.

6. Additionally, why was both income and education included in the models, often these two variables are co-linear? Was this assessed? Are they both necessary in the models?

7. There is no discussion of race and ethnicity. In the US, there is the "healthy immigrant" effect, possible as certain races/ethnicities have not had the weathering from endemic racism. Could a migrant mother and foreign born father have additional discrimination from their race/ethnicity aside from country of origin? Was there data on this? Also consider referencing Collins work (one reference is Collins JW Jr, Wu SY, David RJ. Differing intergenerational birth weights among the descendants of US-born and foreign-born Whites and African Americans in Illinois. Am J Epidemiol. 2002; 155:210-6.)

8. How long were the mothers and father in Norway for and why was this not adjusted for as the authors mention they calculate maternal length of residence and categorize it, but I did not see that data nor why this was not in the models.

Other Minor Edits/By Section:

Abstract

1. Results - Line 46-48 "Unregistered paternal origin and unknown paternal identity were both associated with increased odds of adverse neonatal outcomes." Please clarify in comparison with?

Introduction

1. The introduction seems to simplify a very complex body of literature where paternal identification and origin is intertwined with marital status, race/ethnicity, social economic status and support. This study approaches this by separating out countries of origin of the mother. However, there should be some acknowledgement of additional known paternal effects and birth outcomes.

2. I believe the introduction would be strengthened by more explicitly delineating the gaps in literature, how this study will address the gaps in a novel way in the Introduction.

Methods:

1. Could the choices of what did and did not go into the models be more detailed? Why not consanguinity or paternal age?

2. Can you explain the exclusion factor of second-generation migrant women, does this mean the women were excluded if they were born in Norway but their parents were not or does it mean that the migrant woman was foreign born but her parents were from Norway? What does women with mixed background mean? One parent was from Norway and one not?

3. The information provided in the Setting Section of the Methods was very helpful.

4. It might be helpful to provide examples of which high income countries are most common locations for migrants to originate from.

5. Is there data on previous preterm birth-a big predictor of preterm delivery in the future among the multi-parous, if not should be listed in Discussion as limitation.

6. Any data on maternal high risk pregnancy? Pre-existing morbidities OR pregnancy related diseases-preclampsia or diabetes or obesity that could increase risk of stillbirth and rate of prematurity? If not, should be a limitation in Discussion

7. What about substance use, especially tobacco use which may be higher or lower in certain countries mothers and fathers migrate from? If not, should be in Discussion.

8. Why not report in addition to very and moderately preterm rates, the overall preterm rate?

Results:

1. No bivariate analyses of frequencies reported, only OR and aOR. However, would be helpful to know if the frequencies differ among groups. Were the data in Table1, Figure 2 compared/analyzed? If so should be denoted

2. Why do authors think slightly increased risk of Norwegian-born fathers before adjustment of having moderate preterm birth?

3. For Table 3 Does known father mean known and could be either foreign born or norwegian? If so these might be separated? Either way should be clarified.

Discussion:

1. I think the Discussion could benefit to some restructuring such that limitations are noted together in serial paragraphs where limitations are not just listed but as to why this study is still valid despite the limitations. Foloowed by a strengths paragraph explaining why this study is well designed, novel and important contribution. The current strength paragraph is mixed with limitations. I have noted above some possible limitations to explore.

2. Line 264 which notes that the US study only examined twins. There are other US studies not only of twins. One example is Ma S. Paternal Race/Ethnicity and Birth Outcomes. December 2008, Vol 98, No. 12 | American Journal of Public Health.

3. It may be helpful to discuss more of the biological underpinings of the findings-toxic stress and related inflamation which can lead to poor birth outcomes, how support from a father regardless of marriage may mitigate the inflammation etc.

4. Do the authors surmise that a father from the host population makes a difference due to anything specific to infrastructure in Norway that might not exist in the countries that published the studies the authors cite as background? If so this might also help the reader know why this study is different/may be novel?

Any attachments provided with reviews can be seen via the following link:

[LINK]

3 Jul 2020

Submitted filename: Response to reviewers.docx

Click here for additional data file.

22 Jul 2020

Dear Dr. Vik,

Thank you very much for submitting your manuscript "Associations between paternal origin and adverse neonatal outcomes in births to migrant women: a Norwegian population-based study" (PMEDICINE-D-20-01868R2) for consideration at PLOS Medicine.

Your paper was evaluated by a senior editor and discussed among all the editors here. It was also discussed with an academic editor with relevant expertise, and re-sent to independent reviewers. The reviews are appended at the bottom of this email and any accompanying reviewer attachments can be seen via the link below:

[LINK]

In light of these reviews, I am afraid that we will still not yet be able to accept the manuscript for publication in the journal in its current form, but we would like to consider a revised version that addresses the reviewers' and editors' comments. Obviously we cannot make any decision about publication until we have seen the revised manuscript and your response, and we plan to seek re-review by one or more of the reviewers.

In revising the manuscript for further consideration, your revisions should address the specific points made by each reviewer and the editors. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments, the changes you have made in the manuscript, and include either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please submit a clean version of the paper as the main article file; a version with changes marked should be uploaded as a marked up manuscript.

In addition, we request that you upload any figures associated with your paper as individual TIF or EPS files with 300dpi resolution at resubmission; please read our figure guidelines for more information on our requirements: http://journals.plos.org/plosmedicine/s/figures. While revising your submission, please upload your figure files to the PACE digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at PLOSMedicine@plos.org.

We expect to receive your revised manuscript by Aug 12 2020 11:59PM. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. If new competing interests are declared later in the revision process, this may also hold up the submission. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

Please use the following link to submit the revised manuscript:

https://www.editorialmanager.com/pmedicine/

Your article can be found in the "Submissions Needing Revision" folder.

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see http://journals.plos.org/plosmedicine/s/submission-guidelines#loc-methods.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

We look forward to receiving your revised manuscript.

Sincerely,

Artur Arikainen,

Associate Editor

PLOS Medicine

plosmedicine.org

-----------------------------------------------------------

Requests from the editors:

1. Please address reviewer #3’s comments below.

2. Title: Please update to: “Associations between paternal origin and adverse neonatal outcomes in births to migrant women in Norway: a population-based cohort study”

3. Short Title: Please update to: “Paternal origin and neonatal outcomes in births to migrant women in Norway”

4. Financial Disclosure: Please confirm whether all funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

5. Data Availability Statement (DAS): Please also include an appropriate contact (web and/or email address) for data access inquiries (this cannot be a study author).

6. Abstract:

a. In lines 58-60, please mention the word “limitations” specifically.

b. For p values greater than 0.001, please give the exact value.

c. Lines 50-52, please quantify these results with 95% CIs and p values, even if not significant.

d. Line 51: Please avoid use of italics for emphasis.

e. Line 61: Please begin with “We found that…”

f. Conclusion: Please add a brief note on the ramifications of your study.

7. Author Summary:

a. Lines 80 and 82: Please update to: “…father of the child…”

b. Line 82: Please avoid use of italics for emphasis.

8. Please remove spaces from within the brackets of your citation callouts, eg: “…such as low birth weight [3,4]…”

9. Methods: Please mention explicitly that: “There was no prospective protocol or analysis plan.”

10. Please include the completed STROBE checklist as Supporting Information.

---------------

Comments from the reviewers:

Reviewer #1: The authors have addressed my concerns and I now recommend publication

Peter Flom

Reviewer #3: The authors have done a significant amount of work to respond well to my critiques, especially adding the Norwegian mothers. I still have one major concern remaining:

1. I strongly urge the authors to reconsider their lack of analysis of size for gestational age. Similar to their argument for the concerns of birthweight for gestational age, prematurity is multi-factorial (maternal social factors, maternal genetic factors, maternal chronic disease/overall health, fetal health). Regardless, in general, it is accepted that small for gestational age is a poor birth outcome as prematurity is, and both have been linked to not only maternal factors but also paternal factors. In fact, in the Introduction section, the authors refer to low birth weight (less informative that size for gestational age) as an adverse birth outcome. There are very few birth outcomes based on vital statistics to assess, and size for gestational age or even term low birth weight are both meaningful. The authors have an opportunity to study birthweight for gestational age in this unique population. In fact, just recently, these same authors using a migrant mother/Norwegian birth cohort and birth outcomes similar to this manuscript (but without paternal information) also examined SGA (small for gestational age) status (Vik et al. Country of first birth and neonatal outcomes in migrant and Norwegian-born parous women in Norway: a population based study. BMC Health Services Research (2020) 20:540). It would be interesting for the authors to refer to their BMC Health Services Research publication and compare/contrast SGA and other birth outcome in the current Results and Discussion sections as well.

Any attachments provided with reviews can be seen via the following link:

[LINK]

12 Aug 2020

Submitted filename: Response to reviewer.docx

Click here for additional data file.

25 Aug 2020

Dear Dr. Vik,

Thank you very much for re-submitting your manuscript "Associations between paternal origin and adverse neonatal outcomes in births to migrant women in Norway: a population-based cohort study" (PMEDICINE-D-20-01868R3) for review by PLOS Medicine.

I have discussed the paper with my colleagues and the academic editor and it was also seen again by one reviewer. I am pleased to say that provided the remaining editorial and production issues are dealt with we are planning to accept the paper for publication in the journal.

The remaining issues that need to be addressed are listed at the end of this email. Any accompanying reviewer attachments can be seen via the link below. Please take these into account before resubmitting your manuscript:

[LINK]

Our publications team (plosmedicine@plos.org) will be in touch shortly about the production requirements for your paper, and the link and deadline for resubmission. DO NOT RESUBMIT BEFORE YOU'VE RECEIVED THE PRODUCTION REQUIREMENTS.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

In revising the manuscript for further consideration here, please ensure you address the specific points made by each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper. If you haven't already, we ask that you provide a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract.

We expect to receive your revised manuscript within 1 week. Please email us (plosmedicine@plos.org) if you have any questions or concerns.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.

We look forward to receiving the revised manuscript by Sep 01 2020 11:59PM.

Sincerely,

Artur Arikainen,

Associate Editor

PLOS Medicine

plosmedicine.org

------------------------------------------------------------

Requests from Editors:

1. Title: Please update to: “Paternal country of origin and adverse neonatal outcomes in births to foreign-born women in Norway: a population-based cohort study”

2. Data Availability and Funding Statements: Please update these fields in the online submission form to include the previously requested information. You can remove the sections on lines 17-27.

3. Abstract:

a. Please quantify these results with 95% CIs and p values: “Findings related to unregistered paternal origin were similar for Norwegian-born women.”

b. Please add another limitation at line 66, eg. inability to account for all lifestyle factors.

c. Please correct the data for these statements:

i. “In migrant women, unregistered paternal origin was associated with increased odds of … low Apgar score (3.4% vs 1.5% aOR 1.23; CI 1.99-1.50, p<0.001)” – aOR is given as 2.23 in Table 2.

ii. “In births to Norwegian-born women, a foreign-born father was associated with … decreased odds of moderately preterm birth (4.3% vs 4.4%, aOR 0.95; CI 0.93-0.99, p=0.015)” – CI given as 0.91-0.99 in Table 3.

d. (Please double check all data in the manuscript for accuracy.)

4. Line 100: Please clarify if you mean “international migrant”.

5. Tables:

a. Please ensure all abbreviations are defined in the footnotes.

b. We recommend replacing the vertical bar symbol (|) for footnotes with another symbol (or superscript letters) for clarity, where used.

6. Please ensure that all references are complete – 18 and 49 appear to be missing journal names.

Comments from Reviewers:

Reviewer #3: The authors have sufficiently responded to my critiques.

Any attachments provided with reviews can be seen via the following link:

[LINK]

18 Sep 2020

Dear Mrs. Vik,

On behalf of my colleagues and the academic editor, Dr. Jenny E Myers, I am delighted to inform you that your manuscript entitled "Paternal country of origin and adverse neonatal outcomes in births to foreign-born women in Norway: a population-based cohort study" (PMEDICINE-D-20-01868R4) has been accepted for publication in PLOS Medicine.

PRODUCTION PROCESS

Before publication you will see the copyedited word document (in around 1-2 weeks from now) and a PDF galley proof shortly after that. The copyeditor will be in touch shortly before sending you the copyedited Word document. We will make some revisions at the copyediting stage to conform to our general style, and for clarification. When you receive this version you should check and revise it very carefully, including figures, tables, references, and supporting information, because corrections at the next stage (proofs) will be strictly limited to (1) errors in author names or affiliations, (2) errors of scientific fact that would cause misunderstandings to readers, and (3) printer's (introduced) errors.

If you are likely to be away when either this document or the proof is sent, please ensure we have contact information of a second person, as we will need you to respond quickly at each point.

PRESS

A selection of our articles each week are press released by the journal. You will be contacted nearer the time if we are press releasing your article in order to approve the content and check the contact information for journalists is correct. If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact.

PROFILE INFORMATION

Now that your manuscript has been accepted, please log into EM and update your profile. Go to https://www.editorialmanager.com/pmedicine, log in, and click on the "Update My Information" link at the top of the page. Please update your user information to ensure an efficient production and billing process.

Thank you again for submitting the manuscript to PLOS Medicine. We look forward to publishing it.

Best wishes,

Artur Arikainen,

Associate Editor

PLOS Medicine

plosmedicine.org