Pregnancy complications recur independently of maternal vascular malperfusion lesions.

BACKGROUND: Spontaneous abortions, intrauterine growth restriction, and preeclampsia are thought to be caused by defective placentation and are associated with increased risk of adverse outcomes in subsequent pregnancies. However, it is not known whether the recurrence of adverse outcomes is associated with the recurrence of placental pathology. We hypothesized that recurrent maternal vascular malperfusion (MVM) underlies the recurrence of adverse outcomes.
METHODS: Using data from the National Collaborative Perinatal Project, we assessed the recurrence of pregnancy complications and MVM lesions (N = 3865), associations between a history of spontaneous abortions and MVM lesions or adverse outcomes in subsequent pregnancies (N = 8312), and whether the recurrence of pregnancy complications occurred independently of the presence of MVM lesions.
RESULTS: The odds of an MVM lesion were higher for a woman who had had an MVM lesion in a previous pregnancy (aOR = 1.6; 95% CI 1.3-1.9), although this was marginally non-significant after adjusting for covariates such as gestational age, race and BMI. The odds of preeclampsia, a small-for-gestational-age infant, premature delivery and early pregnancy loss were 2.7-5.0 times higher if there had been that same adverse outcome in a previous pregnancy. A history of spontaneous abortions was associated with higher risk of a small-for-gestational-age baby (aOR = 2.4; 95% CI 1.7-3.4) and prematurity (aOR = 5.1; 95% CI 2.3-11.5 for extremely preterm), but not preeclampsia. The recurrence of adverse outcomes was significant when restricting analyses to women without MVM lesions. Similarly, associations between adverse outcomes and previous spontaneous abortions were significant when statistically controlling for the presence of MVM lesions, or excluding pregnancies with MVM lesions.
CONCLUSIONS: Women with adverse outcomes in one pregnancy are at higher risk of complications in subsequent pregnancies. However, there is significant recurrence of adverse outcomes even in the absence of MVM.

Introduction

Placental dysfunction is thought to underlie diverse adverse pregnancy outcomes, including spontaneous abortions, intrauterine growth restriction, and preeclampsia [1], with spontaneous abortions and later pregnancy complications caused by different degrees of impaired placentation [2]. Consistent with this hypothesis, some circulating markers have been associated with both pregnancy loss and preeclampsia (e.g., PAPP-A [3-6]; sFlt-1, PlGF [7,8]). Furthermore, genetic polymorphisms in certain genes have been associated with both conditions (e.g., VEGF [9-12]; PAPP-A [13,14]; TNF-α [15,16]), potentially suggesting a common genetic susceptibility. Endothelial dysfunction has been proposed as a mechanism that might underlie these shared risks [17].

Given the potential shared etiology between preeclampsia and pregnancy loss, many studies have examined associations between adverse pregnancy outcomes in index pregnancies and spontaneous abortions in previous or subsequent pregnancies. Some find associations between the occurrence of spontaneous abortions and preeclampsia [2,18-23], low birthweight [2,18,20,23-26] and prematurity [2,18,23-27], although not all of these outcomes are consistently observed [28,29].

These studies have not examined the placental pathology that may underlie these associations, but impaired placentation is thought to result in maternal vascular malperfusion (MVM) lesions [30], which are associated with pregnancy complications [31-35]. Indeed, there are associations between MVM lesions in one pregnancy and the incidence of adverse outcomes in a subsequent pregnancy [36,37]. However, the association between MVM in one pregnancy and spontaneous abortion in another has not been investigated. Furthermore, it has not been shown that the recurrence of adverse outcomes in different pregnancies is associated with recurrent MVM pathology.

We hypothesized that certain factors predispose women to recurrent MVM, which increases the risk of spontaneous abortions, preeclampsia, intrauterine growth restriction, and prematurity, and that this mechanism underlies the previously observed associations between spontaneous abortions in one pregnancy and adverse outcomes in another. We therefore predicted that (1) MVM lesions or pregnancy complications in one pregnancy will be associated with an increased risk of MVM lesions or pregnancy complications in the subsequent pregnancy, (2) previous spontaneous abortions will be associated with an increased risk of MVM lesions, (3) previous spontaneous abortions will be associated with an increased risk of adverse outcomes, and (4) pregnancies with MVM lesions will have a higher incidence of adverse outcomes. Finally, if associations between spontaneous abortions and adverse outcomes are due to recurrent placental pathologies, we predict that (5) previous spontaneous abortions will not be associated with an increased risk of adverse outcomes independently of the presence of MVM lesions. We tested our predictions using data from the National Collaborative Perinatal Project.

Materials and methods

The National Collaborative Perinatal Project (NCPP) has been described elsewhere [38], and its data are publicly available (https://catalog.archives.gov/id/606622). As we have described previously [39], in over 90% of pregnancies, maternal race was categorized as white or black, and so analyses were restricted to these two races. We used only singleton pregnancies where offspring sex was assigned male or female; fetal and neonatal deaths were included, and cases were not excluded on the basis of maternal health conditions or congenital abnormalities. We excluded pregnancies where the gestational age was over 43 weeks; gestational age was calculated based on the last menstrual period to the nearest week. Within each gestational age category (described below), birthweights and placental weights were corrected for maternal race, offspring sex and gestational age using a general linear model, after first removing the top and bottom 0.5% of raw birthweights and placenta weights within each gestational age category to objectively exclude biologically implausible values [40]. Pregnancies ending before 24 weeks were excluded from all analyses except those of spontaneous abortions.

Outcomes

To assess prematurity, we used a lower limit for gestational age based on the limit of viability [41], but otherwise used World Health Organization categories, i.e., extremely preterm (24 to 27 weeks, inclusive), very preterm (28 to 32 weeks, inclusive), moderate to late preterm (32 to 37 weeks, inclusive) and term (38 to 43 weeks, inclusive). In addition to prematurity, outcomes included spontaneous abortion (i.e., gestational age less than 20 weeks), small for gestational age (SGA, i.e., corrected birthweight below the 10th percentile), preeclampsia (yes/no), survival (categorized as fetal death, death between birth and 120 days of age, or survival past 120 days), Apgar score at 1 and 5 minutes (categorized as 0–3, 4–6, or 7–10, where larger numbers are better). For preeclampsia, the rare cases of eclampsia were categorized as “yes”, whereas “mild” preeclampsia was categorized as “no” because MVM lesions are more strongly associated with severe preeclampsia [30]. Preeclampsia was categorized as severe if one or more of the following symptoms was present: systolic blood pressure of 160 mmHg or higher, diastolic blood pressure of 110 mmHg or higher (on at least two occasions at least six hours apart), proteinuria of 5 grams or more, oliguria (400 cc or less in 24 hours), cerebral or visual disturbances, or pulmonary edema or cyanosis.

MVM lesions

The NCPP data were collected > 50 years ago, and a comparison of variables available in the NCPP with lesions currently used to define MVM is provided in Table 1. MVM lesions included the presence of decidua vessel thrombosis, fibrinoid or atheroma, excessive fibrin deposition in the cytotrophoblast, at least one infarct measuring 3 cm or more, presence of hemorrhage, and syncytium-nuclear clumping that is excessive for term in a term placenta, or normal for term in a preterm placenta. While accelerated villous maturation is often included as an MVM lesion [42], it is difficult to diagnose in term placentas [39], and so syncytial clumping was used instead. We used two different approaches to establish evidence of MVM: (A) corrected placenta weight below the 10th percentile and one of the MVM lesions described above [33,43] (which we term “MVMnarrow”), or (B) one of the MVM lesions described, irrespective of placental weight [31,35] (which we term “MVMbroad”). Although not all of the lesions currently used to define MVM were available in the NCPP data, there is substantial variability in the criteria used among recent studies (Table 1), such that our study is as similar to some recent studies as the recent studies are to each other. We did not assess MVM for placentas with gestational age below 24 weeks, and so no analyses examined the association between spontaneous abortion and MVM lesions. Placental data were collected at 12 institutions. To reduce potential bias due to inconsistent collection of data, we excluded all data from 3 institutions where placental pathology data were available for less than 75% percent of pregnancies.

Table 1

Comparison of lesions currently used to define MVM and variables available in NCPP data.

Current MVM criteria	NCPP variables
decidual vasculopathy[31,35,37,44,45], decidual vascular thrombosis[31]; decidual arteriopathy[30,42]; arterial thrombosis[42]	decidua vessel thrombosis
fibrinoid changes/necrosis in decidual vessels[31]; fibrinoid necrosis[42]	decidua vessel fibrinoid
acute atherosis[31,42], decidual vasculopathy atherosis[43];	decidua vessel atheroma
increased perivillous fibrin[31]; increased perivillous fibrin deposition[35,37]; increased intervillous fibrin deposition[35,37]; fibrinoid deposition[44]	excessive fibrin deposition in the cytotrophoblast (as defined in NCPP documentation, “this refers to the fibrin or fibrinoid deposits which occur in cytotrophoblast cells as term is approached”)
infarction[31,42]; villous infarction[35,37]; infarcts[44]; central (> 1 cm), full-thickness or multi-focal infarction[43]; placental infarction[30]; placental infarcts[45]; macroscopic infarction >5% of the placental parenchyma[46]; multifocal infarction[33]	at least one infarct measuring 3 cm or more
hypermature chorionic villi[31]; accelerated villous maturation[30,31,42–46]; advanced villous maturation[35,37]; increased syncytial knot prevalence[42]; abnormal placental villi[33]	syncytium-nuclear clumping that is excessive for term in a term placenta, or normal for term in a preterm placenta
low placental weight (placental weight<10th percentile)[33,42–44,46]; placental hypoplasia[30,42]	corrected placenta weight below the 10th percentile
retroplacental hematoma[31]; retroplacental hemorrhage[30,33,42]	presence of hemorrhage on maternal surface or depressed area caused by hemorrhage
distal villous hypoplasia[30,42,46]; mural hypertrophy[42]; chronic perivasculitis[42]; absence of spiral artery remodeling [42]; persistence of intramural endovascular trophoblast in the third trimester [42]; increased circulating nucleated red blood cells (NRBC)[46]; ischemia and shock villi [46]; eosinophilic necrosis of decidual arterial walls[43]	not described

Covariates

Gestational age, maternal age, maternal race, maternal body mass index (BMI), smoking (yes/ no) and interpregnancy interval were included as covariates. Maternal BMI was categorized as underweight (< 18.5), normal (18.5–25), overweight (>25–30) or obese (> 30). Interpregnancy interval was defined as the period between the end of the previous pregnancy and the last menstrual period before the current pregnancy, and was categorized as short (less than 18 months), medium (18 to 59 months, inclusive) or long (greater than 59 months), based on previously-reported associations with adverse outcomes [47,48].

Recurrence of outcomes and pathology

To examine the recurrence of outcomes and pathology, we included only women with more than one singleton pregnancy in the dataset and compared the second eligible pregnancy in the dataset with the first. These criteria yielded 5889 eligible women. Excluding 440 women for whom the gestational age of the first and/ or second pregnancy was below 24 weeks, for which we did not assess MVM, there were 5449 women; assessment of MVM was available for both pregnancies for 3865 of these women. Comparison of characteristics of pregnancies with and without MVM data is provided in the Table in S1 Table, including both women with and without more than one singleton pregnancy (study population described below). In the recurrence dataset, only 18 index pregnancies had an interpregnancy interval greater than 59 months and so these pregnancies were excluded from analyses involving interpregnancy interval.

Associations between previous spontaneous abortions, MVM lesions, and outcomes

To examine associations between previous spontaneous abortions and outcomes, we compared women with 3 or more pregnancy losses at less than 20 weeks, with women with no prior losses (but at least one prior pregnancy), no record of sterility or infertility whose current pregnancy was conceived in 6 months or less. In both groups, we excluded women with more than 3 prior livebirths to ensure that the previous loss group included only women for whom at least half of previous pregnancies were losses, and not women who had had multiple losses simply as a result of numerous pregnancies. Where a woman had more than one pregnancy included in the NCCP, we included only her first study pregnancy. These criteria yielded 18077 eligible pregnancies. Excluding 3638 pregnancies with gestational age below 24 weeks (for which we did not assess MVM), there were 14439 pregnancies, of which assessment of MVM was available for 11753; comparison of characteristics of pregnancies with and without missing placental data is provided in the Table in S1 Table. For analyses including previous losses, 8312 pregnancies were available; 3199 pregnancies with 1 or 2 prior losses were excluded because we compared women with 3 or more pregnancy losses with no prior losses.

Statistical analyses

Birthweight and placental weight were corrected for maternal race, offspring sex and gestational age using a general linear model (proc GLM, SAS, Version 9.4). Pregnancy outcomes and the presence of MVM lesions were analysed using logistic regression (proc LOGISTIC, SAS, Version 9.4).

Results

Prediction 1: MVM lesions or pregnancy complications in one pregnancy will be associated with an increased risk of MVM lesions or pregnancy complications in the subsequent pregnancy

Among women with more than one singleton pregnancy in the dataset, MVMbroad lesions in one pregnancy were associated with increased odds of MVMbroad lesions in the subsequent pregnancy (aOR = 1.6), although after adjusting for covariates such as gestational age, race and BMI, this was marginally non-significant (aOR = 1.2, P = 0.06, Table 2). Although the aOR for MVMnarrow lesions was similar to that for MVMbroad lesions, the recurrence was not significant, with or without adjustment for covariates, likely due to their very low frequency (Table 2). Preeclampsia, SGA, prematurity, spontaneous abortion, and poor Apgar scores in one pregnancy were associated with increased odds of the same adverse outcome occurring in the subsequent pregnancy, even after adjusting for interpregnancy interval, gestational age, maternal race, maternal BMI and smoking (Table 2). Adjusted odds ratios for the recurrence of adverse outcomes were highest for preeclampsia, SGA and prematurity (5.0, 4.6 and 3.7 respectively) and lowest for Apgar scores at 1 minute (1.4). Fetal and neonatal death did not show significant recurrence after correction for covariates, of which gestational age and race were significant (Table 2).

Table 2

Recurrence of MVM and pregnancy outcomes between pregnancies.

		Occurrence in previous pregnancy1		Odds ratio2	P-value	Adjusted odds ratio3	P-value	Other significant terms in model4
	Occurrence in index pregnancy	Yes # (%)	No # (%)	(95% CI)		(95% CI)
MVMnarrow	Yes	2 (3.2)	60 (96.8)	1.5 (0.4–6.1)	0.59	1.4 (0.3–5.9)	0.65	Gestational age (P < 0.0001); Race (P = 0.006)
	No	84 (2.2)	3719 (97.8)
MVMbroad	Yes	261 (29.8)	616 (70.2)	1.6 (1.3–1.9)	0.0001	1.2 (1.0–1.5)	0.06	Gestational age (P < 0.0001); Race (P = 0.02); BMI (P = 0.02)
	No	655 (21.1)	2446 (78.9)
Preeclampsia	Yes	18 (19.8)	73 (80.2)	6.5 (3.8–11.2)	0.0001	5.0 (2.9–8.7)	0.0001	Race (P < 0.0001); BMI (P < 0.002)
	No	170 (3.6)	4498 (96.4)
SGA	Yes	145 (31.1)	322 (68.9)	5.2 (4.2–6.5)	0.0001	4.6 (3.7–5.8)	0.0001	Smoking (P < 0.0001)
	No	385 (8.0)	4440 (92.0)
Prematurity	Extreme	32 (40.5)	47 (59.5)	4.3 (2.7–6.8)	0.0001	3.7 (2.3–5.9)	0.0001	Race (P < 0.0001); BMI (P = 0.0004)
	Very	91 (43.3)	119 (56.7)	4.8 (3.6–6.4)		3.8 (2.8–5.1)
	Moderate	369 (40.7)	537 (59.3)	4.3 (3.7–5.1)		3.7 (3.1–4.3)
	Term	583 (13.7)	3671 (86.3)
Spontaneous abortion before 20 weeks	Yes	15 (9.2)	149 (90.9)	3.0 (1.7–5.3)	0.0001	2.7 (1.5–5.1)	0.001	Race (P = 0.04); BMI (P = 0.02)
	No	184 (3.2)	5541 (96.8)
Survival	Fetal death	11 (12.6)	76 (87.4)	3.8 (2.0–7.2)	0.0001	2.3 (1.0–5.0)	0.11	Gestational age (P < 0.0001); Race (P = 0.01)
	Death before 120 days	10 (8.0)	115 (92.0)	2.3 (1.2–4.4)		1.5 (0.7–3.0)
	Survival past 120 days	193 (3.7)	5044 (96.3)
Apgar score at 1 minute	0–3	55 (28.4)	139 (71.6)	1.6 (1.2–2.2)	0.0002	1.5 (1.1–2.1)	0.0006	Gestational age (P < 0.0001)
	4–6	147 (25.7)	424 (74.3)	1.4 (1.1–1.7)		1.4 (1.2–1.7)
	7–10	747 (19.8)	3028 (80.2)
Apgar score at 5 minutes	0–3	9 (14.8)	52 (85.3)	3.9 (1.9–8.0)	0.0002	3.1 (1.4–6.6)	0.006	Gestational age (P < 0.0001)
	4–6	9 (8.3)	99 (91.7)	2.0 (1.0–4.1)		1.8 (0.9–3.6)
	7–10	195 (4.3)	4350 (95.7)

1 For outcomes with multiple levels of adverse outcomes, all levels of adverse outcome (e.g., extreme, very and moderate preterm) were combined for the previous pregnancy.

2 All odds ratios were calculated as the odds of the adverse outcome relative to the odds of the best outcome where there were multiple levels of adverse outcomes.

3 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal race, maternal BMI and smoking. Analyses of prematurity and spontaneous abortion before 20 weeks did not include gestational age.

4 Adjusted odds ratios for other terms are provided in the Table in S3 Table.

To assess whether the recurrence of pregnancy complications occurred in the absence of recurrent MVM lesions, we restricted analyses to women who showed no MVM lesion in either pregnancy. Preeclampsia, SGA and prematurity in one pregnancy were associated with increased odds of the same adverse outcome occurring in the subsequent pregnancy after adjusting for covariates (Table in S2 Table). Moreover, the adjusted odds ratios were similar whether women with MVM lesions were excluded (Table in S2 Table) or not (Table 2) for the recurrence of preeclampsia (excluding: 4.9–5.2 vs. not excluding: 5.0), SGA (4.1–4.6 vs. 4.6) and prematurity (3.3–8.7 vs. 3.7). Similar results were observed whether using our “narrow” or “broad” criteria for MVM lesions, although the recurrence of Apgar scores was not statistically significant when excluding pregnancies showing MVMbroad lesions (Table in S2 Table). Given the broader inclusion criteria, MVMbroad lesions were frequent (Table 2) and so their exclusion reduced sample sizes substantially, reducing statistical power.

Prediction 2: Previous spontaneous abortions will be associated with an increased risk of MVM lesions in index pregnancy

We compared women with 3 or more pregnancy losses at less than 20 weeks with women with no prior losses. Previous spontaneous abortions were associated with increased odds of MVMnarrow lesions (aOR = 2.2), but not MVMbroad lesions (aOR = 0.9), in the index pregnancy when adjusting for interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking (Table 3).

Table 3

Associations between previous spontaneous abortions and pregnancy outcomes.

		Previous spontaneous abortions		Odds ratio1	P-value	Adjusted odds ratio2	P-value	Other significant terms in model3
	Occurrence in index pregnancy	Yes # (%)	No # (%)	(95% CI)		(95% CI)
MVMnarrow	Yes	12 (7.0)	160 (93.0)	3.0 (1.6–5.5)	0.0003	2.2 (1.2–4.4)	0.02	Interpregnancy interval (P = 0.04); Gestational age (P < 0.0001)
	No	198 (2.4)	7942 (97.6)
MVMbroad	Yes	53 (2.7)	1879 (97.3)	1.1 (0.8–1.5)	0.60	0.9 (0.6–1.3)	0.51	Gestational age (P < 0.0001)
	No	165 (2.5)	6368 (97.5)
Preeclampsia	Yes	8 (3.3)	234 (96.7)	1.4 (0.7–2.8)	0.38	1.1 (0.5–2.4)	0.72	Age (P = 0.001); Gestational age (P = 0.03); Race (P < 0.0001); BMI (P < 0.0001); Smoking (P = 0.03)
	No	224 (2.4)	9056 (97.6)
SGA	Yes	50 (5.9)	801 (94.1)	2.8 (2.0–3.9)	0.0001	2.4 (1.7–3.4)	0.0001	Age (P = 0.004); Gestational age (P = 0.008); BMI (P < 0.0001); Smoking (P < 0.0001)
	No	199 (2.2)	8983 (97.8)
Prematurity	Extreme	9 (8.7)	95 (91.3)	3.8 (1.9–7.5)	0.0009	5.1 (2.3–11.5)	0.0001	Age (P = 0.02); Race (P < 0.0001); BMI (P < 0.0001); Smoking (P < 0.0001)
	Very	13 (4.1)	302 (95.9)	1.7 (1.0–3.0)		2.2 (1.2–4.1)
	Moderate	41 (2.6)	1522 (97.4)	1.1 (0.8–1.5)		1.3 (0.9–1.8)
	Term	201 (2.5)	7966 (97.5)
Spontaneous abortion before 20 weeks	Yes	21 (10.8)	174 (89.2)	4.4 (2.8–7.0)	0.0001	2.1 (1.2–3.6)	0.005	Interpregnancy interval (P = 0.0002); Age (P < 0.0001); BMI (P = 0.03); Smoking (P = 0.05)
	No	272 (2.7)	9932 (97.3)
Survival	Fetal death	18 (13.3)	117 (86.7)	6.2 (3.7–10.3)	0.0001	4.6 (2.3–9.0)	0.0001	Interpregnancy interval (P = 0.01); Gestational age (P < 0.0001); Race (P = 0.006)
	Death before 120 days	7 (3.5)	195 (96.5)	1.4 (0.7–3.1)		1.3 (0.6–3.0)
	Survival past 120 days	239 (2.4)	9573 (97.6)
Apgar score at 1 minute	0–3	19 (4.5)	405 (95.5)	2.1 (1.3–3.4)	0.001	1.8 (1.1–3.0)	0.02	Interpregnancy interval (P = 0.002); Age (P = 0.03); Gestational age (P < 0.0001); Race (P < 0.03)
	4–6	39 (3.4)	1110 (96.6)	1.6 (1.1–2.2)		1.5 (1.0–2.1)
	7–10	166 (2.2)	7428 (97.8)
Apgar score at 5 minutes	0–3	9 (8.1)	102 (91.9)	3.6 (1.8–7.2)	0.001	4.5 (2.0–10.1)	0.0007	Interpregnancy interval (P = 0.02); Gestational age (P < 0.0001)
	4–6	4 (1.6)	240 (98.4)	0.7 (0.2–1.8)		0.6 (0.2–1.6)
	7–10	216 (2.4)	8754 (97.6)

1 All odds ratios were calculated as the odds of the adverse outcome relative to the odds of the best outcome where there were multiple levels of adverse outcomes.

2 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking. Analyses of prematurity and spontaneous abortion before 20 weeks did not include gestational age.

3 Adjusted odds ratios for other terms are provided in the Table in S4 Table.

Prediction 3: Previous spontaneous abortions will be associated with an increased risk of adverse outcomes in index pregnancy

Adjusting for covariates, previous spontaneous abortions were associated with increased odds of SGA (aOR = 2.4), extremely (aOR = 5.1) or very preterm birth (aOR = 2.2), spontaneous abortion before 20 weeks (aOR = 2.1), fetal death at 24 weeks or later (aOR = 4.6), and low Apgar scores at 1 (aOR = 1.8) and 5 minutes (aOR = 4.5; Table 3). Previous spontaneous abortions were not associated with increased odds of preeclampsia (aOR = 1.1; Table 3).

Prediction 4: Pregnancies with MVM lesions will have a higher incidence of adverse outcomes

The presence of MVM, defined using our “narrow” criteria, was associated with increased odds of preeclampsia (aOR = 2.6), SGA (aOR = 11.5), prematurity (aOR = 3.9–4.7), and fetal death (aOR = 12.5), before and after adjustment for covariates (Table 4). Using our “broad” criteria, MVM lesions were associated with higher odds of SGA (aOR = 1.2) and prematurity (aOR = 9.8–24.7), and fetal death (aOR = 2.1) but not preeclampsia or Apgar scores after adjustment for covariates (Table 5).

Table 4

Associations between MVMnarrow lesions and pregnancy outcomes.

		MVMnarrow		Odds ratio1	P-value	Adjusted odds ratio2	P-value	Other significant terms in model
	Occurrence in pregnancy	Yes # (%)	No # (%)	(95% CI)		(95% CI)
Preeclampsia	Yes	14 (4.6)	294 (95.4)	2.4 (1.4–4.1)	0.002	2.6 (1.5–4.6)	0.0009	Age (P < 0.0001); Race (P < 0.0001); BMI (P < 0.0001); Smoking (P = 0.01)
	No	213 (2.0)	10621 (98.0)
SGA	Yes	115 (10.9)	943 (89.1)	10.2 (7.9–13.3)	0.0001	11.5 (8.7–15.2)	0.0001	Age (P = 0.0003); Gestational age (P < 0.0001); BMI (P < 0.0001); Smoking (P < 0.0001)
	No	125 (1.2)	10495 (98.8)
Prematurity	Extreme	6 (6.0)	94 (94.0)	4.5 (1.9–10.6)	0.0001	4.7 (2.0–11.0)	0.0001	Age (P = 0.02); Race (P < 0.0001); BMI (P < 0.0001); Smoking (P < 0.0001)
	Very	21 (6.2)	318 (93.8)	4.7 (2.9–7.6)		4.7 (2.9–7.8)
	Moderate	89 (5.2)	1625 (94.8)	3.9 (3.0–5.1)		3.9 (2.9–5.2)
	Term	133 (1.4)	9467 (98.6)
Survival	Fetal death	34 (26.0)	97 (74.0)	19.2 (12.7–29.1)	0.0001	12.5 (7.8–19.9)	0.0001	Interpregnancy interval (P = 0.05); Age (P = 0.001); Gestational age (P < 0.0001); Race (P = 0.008)
	Death before 120 days	11 (4.7)	225 (95.3)	2.7 (1.4–5.0)		1.7 (0.9–3.3)
	Survival past 120 days	204 (1.8)	11182 (98.2)
Apgar score at 1 minute	0–3	20 (3.7)	526 (96.3)	2.2 (1.4–3.5)	0.005	1.6 (1.0–2.7)	0.10	Interpregnancy interval (P = 0.002); Age (P = 0.008); Gestational age (P < 0.0001); BMI (P < 0.02)
	4–6	24 (1.6)	1436 (98.4)	1.0 (0.6–1.5)		0.9 (0.6–1.4)
	7–10	154 (1.7)	8820 (98.3)
Apgar score at 5 minutes	0–3	6 (4.6)	124 (95.4)	2.8 (1.2–6.4)	0.0002	1.6 (0.6–4.1)	0.02	Interpregnancy interval (P = 0.02); Gestational age (P < 0.0001)
	4–6	13 (4.6)	272 (95.4)	2.8 (1.6–4.9)		2.2 (1.2–3.9)
	7–10	183 (1.7)	10556 (98.3)

1 All odds ratios were calculated as the odds of the adverse outcome relative to the odds of the best outcome where there were multiple levels of adverse outcomes.

2 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking. Analyses of prematurity did not include gestational age.

Table 5

Associations between MVMbroad lesions and pregnancy outcomes.

		MVMbroad		Odds ratio1	P-value	Adjusted odds ratio2	P-value	Other significant terms in model
	Occurrence in pregnancy	Yes # (%)	No # (%)	(95% CI)		(95% CI)
Preeclampsia	Yes	83 (26.3)	232 (73.7)	1.3 (1.0–1.6)	0.09	1.2 (0.9–1.6)	0.24	Age (P < 0.0001); Race (P < 0.0001); BMI (P < 0.0001); Smoking (P = 0.03)
	No	2455 (22.3)	8576 (77.7)
SGA	Yes	264 (24.3)	820 (75.7)	1.1 (1.0–1.3)	0.10	1.2 (1.0–1.4)	0.02	Interpregnancy interval (P = 0.03); Age (P = 0.0002); Gestational age (P < 0.0005); BMI (P < 0.0001); Smoking (P < 0.0001)
	No	2388 (22.1)	8399 (77.9)
Prematurity	Extreme	69 (68.3)	32 (31.7)	14.0 (9.2–21.4)	0.0001	14.8 (9.6–22.8)	0.0001	Race (P < 0.0001); BMI (P < 0.0001); Smoking (P < 0.0001)
	Very	272 (78.4)	75 (21.6)	23.6 (18.2 = 30.7)		24.7 (18.8–32.3)
	Moderate	1042 (59.6)	707 (40.4)	9.6 (8.6–10.7)		9.8 (8.8–11.1)
	Term	1301 (13.3)	8473 (86.7)
Survival	Fetal death	90 (62.5)	54 (37.5)	6.1 (4.3–8.5)	0.0001	2.1 (1.4–3.1)	0.0001	Age (P < 0.0001); Gestational age (P < 0.0001); Race (P = 0.003)
	Death before 120 days	100 (41.0)	144 (59.0)	2.5 (1.9–3.3)		0.7 (0.5–0.9)
	Survival past 120 days	2494 (21.5)	9089 (78.5)
Apgar score at 1 minute	0–3	165 (29.6)	392 (70.4)	1.6 (1.3–1.9)	0.0001	1.0 (0.8–1.2)	0.53	Interpregnancy interval (P = 0.001); Age (P = 0.007); Gestational age (P < 0.0001); BMI (P < 0.02)
	4–6	349 (23.6)	1132 (76.4)	1.2 (1.0–1.3)		1.1 (0.9–1.3)
	7–10	1918 (21.0)	7214 (79.0)
Apgar score at 5 minutes	0–3	54 (40.6)	79 (59.4)	2.5 (1.8–3.6)	0.0001	0.7 (0.4–1.0)	0.15	Interpregnancy interval (P = 0.02); Gestational age (P < 0.0001)
	4–6	93 (31.9)	199 (68.2)	1.7 (1.3–2.2)		0.9 (0.7–1.2)
	7–10	2332 (21.4)	8586 (78.64)

1 All odds ratios were calculated as the odds of the adverse outcome relative to the odds of the best outcome where there were multiple levels of adverse outcomes.

2 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking. Analyses of prematurity did not include gestational age.

Prediction 5: Previous spontaneous abortions will not be associated with an increased risk of adverse outcomes independently of the presence of MVM lesions

Adjusting for covariates including the presence of MVM lesions, previous spontaneous abortions were associated with increased odds of SGA, prematurity and fetal death at 24 weeks or later, and lower Apgar scores at 1 and 5 minutes (Table 6). Results were similar whether using our narrow or broad criteria to define the presence of MVM lesions. Adjusted odds ratios for the association with previous spontaneous abortions were similar whether adjusting for the presence of MVM lesions (Table 6) or not (Table 3) for SGA (adjusting for MVM lesions: 1.9–2.2 vs. not adjusting: 2.4), prematurity (2.9–3.1 vs. 2.2 for very premature birth), and fetal death (4.5–5.0 vs. 4.6). Previous spontaneous abortions were not associated with preeclampsia with (Table 6) or without (Table 3) inclusion of MVM lesions (defined using narrow or broad criteria) in the model.

Table 6

Associations of previous spontaneous abortions and pregnancy outcomes including the presence of MVM lesions as a covariate.

	Including MVMnarrow as a covariate				Including MVMbroad as a covariate
	Effect of previous spontaneous abortions		Effect of MVM		Effect of previous spontaneous abortions		Effect of MVM
	aOR1	P-value	aOR1	P-value	aOR1	P-value	aOR1	P-value
Preeclampsia	1.0 (0.4–2.4)	0.98	3.5 (1.8–6.7)	0.0002	1.2 (0.5–2.7)	0.69	1.3 (0.9–1.9)	0.14
SGA	1.9 (1.3–2.9)	0.002	10.6 (7.5–15.0)	0.0001	2.2 (1.5–3.2)	0.0001	1.2 (1.0–1.5)	0.04
Prematurity		0.002		0.0001		0.0005		0.0001
Extreme	4.1 (1.3–12.5)		3.1 (0.9–10.2)		5.7 (2.0–16.4)		14.0 (8.3–23.4)
Very	2.9 (1.5–5.6)		4.0 (2.2–7.2)		3.1 (1.5–6.3)		29.7 (21.4–41.1)
Moderate	1.3 (0.8–1.9)		3.5 (2.5–4.9)		1.3 (0.8–2.1)		9.9 (8.6–11.3)
Survival		0.006		0.0001		0.0008		0.008
Fetal death	4.5 (1.8–11.3)		15.4 (8.6–27.6)		5.0 (2.2–11.6)		2.0 (1.2–3.4)
Death before 120 days	1.1 (0.4–2.8)		1.4 (0.6–3.3)		1.1 (0.4–2.7)		0.8 (0.5–1.1)
Apgar at 1 minute		0.03		0.18		0.02		0.14
0–3	1.6 (0.9–2.9)		1.8 (0.9–3.2)		1.8 (1.0–3.1)		1.3 (1.0–1.7)
4–6	1.6 (1.1–2.4)		0.9 (0.5–1.6)		1.6 (1.1–2.3)		1.1 (0.9–1.3)
Apgar at 5 minutes		0.0009		0.08		0.001		0.30
0–3	5.1 (2.0–12.5)		2.2 (0.8–6.2)		5.0 (2.0–12.2)		0.7 (0.4–1.1)
4–6	0.5 (0.2–1.7)		2.0 (0.9–4.1)		0.5 (0.2–1.7)		0.9 (0.6–1.3)

1 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking. Analyses of prematurity did not include gestational age.

Restricting analyses to pregnancies with no signs of MVM lesions, previous spontaneous abortions remained associated with increased odds of SGA, prematurity, and lower Apgar scores (Table 7). However, the association between previous spontaneous abortions and fetal death at 24 weeks or later was no longer significant when removing pregnancies with MVM lesions (Table 7). Similar results were observed whether using our “narrow” or “broad” criteria for MVM lesions (Table 7). Adjusted odds ratios were similar whether pregnancies with MVM lesions were removed (Table 7) or not (Table 3) for SGA (excluding pregnancies with MVM lesions: 1.8 vs. including: 2.4) and prematurity (2.7–3.8 vs. 2.2 for very premature birth).

Table 7

Associations of previous spontaneous abortions and pregnancy outcomes excluding cases with MVM lesions.

	Excluding MVMnarrow lesions		Excluding MVMbroad lesions
	aOR1	P-value	aOR1	P-value
Preeclampsia	0.8 (0.3–2.1)	0.71	1.0 (0.4–2.9)	0.96
SGA	1.8 (1.1–2.8)	0.01	1.8 (1.2–2.9)	0.01
Prematurity		0.003		0.003
Extreme	4.7 (1.5–14.3)		12.0 (2.3–63.5)
Very	2.7 (1.3–5.4)		3.8 (1.2–12.0)
Moderate	1.3 (0.8–1.9)		1.3 (0.7–2.3)
Survival		0.12		0.54
Fetal death	2.9 (1.0–8.8)		1.7 (0.3–9.1)
Death before 120 days	0.7 (0.2–2.2)		0.5 (0.1–2.4)
Apgar at 1 minute		0.03		0.04
0–3	1.6 (0.9–3.0)		1.9 (1.0–3.8)
4–6	1.6 (1.1–2.4)		1.6 (1.0–2.4)
Apgar at 5 minutes		0.03		0.15
0–3	3.5 (1.3–9.5)		3.2 (0.9–12.0)
4–6	0.5 (0.2–1.8)		0.5 (0.1–2.3)

1 Adjusted odds ratios are from logistic regression including interpregnancy interval, gestational age, maternal age, maternal race, maternal BMI and smoking. Analyses of prematurity did not include gestational age.

Discussion

MVM lesions are thought to reflect placental dysfunction that may underlie spontaneous abortions, preeclampsia and intrauterine growth restriction. We examined whether recurrence of pathology might underlie the recurrence of adverse outcomes. The odds of an MVM lesion were 1.6 times higher for a woman who had had an MVM lesion in a previous pregnancy, using our broad definition of MVM lesions, although this was marginally non-significant after adjustment for covariates. The odds of an adverse outcome were 2.7–4.9 times higher if there had been that adverse outcome in a previous pregnancy. As described by others [2,18,20,23-27], previous spontaneous abortions were associated with 2.4 times higher odds of SGA and 5.1 times higher odds of extreme prematurity. Furthermore, we also showed that previous spontaneous abortions were associated with increased risk of low Apgar scores. However, we did not find an association between previous spontaneous abortions and preeclampsia.

The presence of MVM lesions was associated with higher odds of preeclampsia, SGA, prematurity, and fetal death, as previously observed [30], as well as low Apgar scores. These observations, largely consistent with previous work, led us to hypothesize that the associations between previous spontaneous abortions and subsequent adverse outcomes, and the recurrence of the same adverse outcome, were due to the recurrence of MVM lesions. However, the associations between previous spontaneous abortions and adverse outcomes generally remained significant and similar in magnitude even when controlling for the presence MVM lesions, or when removing pregnancies with MVM lesions. Furthermore, among women with more than one pregnancy in the dataset, the recurrence of adverse outcomes was significant when restricting analyses to women without MVM lesions in either pregnancy. These results suggested that the recurrence of adverse outcomes, and the associations between spontaneous abortions and adverse outcomes in subsequent pregnancies, can occur independently of recurrent MVM lesions. While it is possible that recurrent pathology did account for some cases of recurrent adverse outcomes, the adjusted odds ratios for associations with previous abortions and for the recurrence of adverse outcomes were generally not reduced by controlling for the presence MVM lesions or removing pregnancies with MVM lesions, suggesting that a substantial component of recurrence risk is independent of pathology. Previous studies have shown that the presence of MVM in one pregnancy is associated with increased risk of adverse outcome in a subsequent pregnancy [36,37,49]. Our results indicate that the MVM lesion itself does not have to recur to result in an adverse outcome, and suggest that other, unmeasured confounding factors may be responsible for these associations.

We used two different approaches described in the literature to define the presence of MVM, differing only in whether low placental weight was required for diagnosis (MVMnarrow) [33,43] or not (MVMbroad) [31,35]. The two approaches generally yielded similar results, except that MVMnarrow lesions were associated with higher odds of preeclampsia whereas MVMbroad lesions were not. These results suggest that the “narrow” approach provided a more specific, informative diagnosis.

Approximately 2% of placentas showed MVMnarrow lesions whereas 23% showed MVMbroad lesions. Our prevalence of MVMbroad lesions is lower than previous reports (30.5% [35]; 35.7% [50]; 39.9% [31]; 46.7–49.7% [44]), perhaps because healthy pregnancies were less likely to have been examined in some of these other studies. Our prevalence of MVMnarrow lesions is similar to that in studies that used a similar definition (8.4% [33]; 0–4.2% including ethnicities included in the present study [43]).

We acknowledge that our study used data collected > 50 years ago, and that assessment of placental pathology has changed in that time. For example, the term distal villous hypoplasia was not used in the histological assessment of the placentas. Despite this, our observed rates of MVMnarrow are in the range of those of more recent studies, as discussed above. A strength of the present study is that placental pathology was performed consistently and collected for healthy, uncomplicated pregnancies, with pathology data available for over 80% of pregnancies. Moreover, we reproduced the association between MVM lesions and preeclampsia [31,33,35]. Furthermore, the lesions used to define MVM are not consistent among current studies (Table 1), and some authors require lesions to be combined with low placental weight whereas others do not, resulting in very different rates of MVM. We investigated both approaches, and the criteria we used were very similar to some recent work. Finally, while the assessment of pathology has evolved, the biology underlying the pathology and the associations between placental function and adverse outcomes are not expected to have changed.

Conclusions

Women with spontaneous abortions or other adverse outcomes in a previous pregnancy are at higher risk of adverse outcomes in subsequent pregnancies. However, the recurrence of outcomes thought to be associated with MVM lesions occurs even in the absence of placental pathology. In many cases, the recurrence of an adverse outcomes may not be due to an intrinsic predisposition to a specific placental pathology, but rather may be caused by other aspects of maternal physiology beyond the placenta.

Characteristics of pregnancies with and without missing placental data, including only pregnancies at 24 weeks or later and excluding 3 institutions where placental pathology data were available for less than 75% percent of pregnancies.

(DOCX)

Click here for additional data file.

Recurrence of outcomes between pregnancies, restricting analyses to women not showing MVM lesions in either pregnancy.

(DOCX)

Click here for additional data file.

Adjusted odds ratios for all covariates in analyses of recurrence of MVM and pregnancy outcomes between pregnancies.

(DOCX)

Click here for additional data file.

Adjusted odds ratios for all covariates in analyses of effects of previous spontaneous abortions on pregnancy outcomes.

(DOCX)

Click here for additional data file.

20 Dec 2019

PONE-D-19-32724

Pregnancy complications recur independently of maternal vascular malperfusion lesions

PLOS ONE

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https://doi.org/10.1016/j.placenta.2019.01.012

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Reviewer #1: The authors take advantage of the large number of patients followed and the high quality placental pathology in the Collaborative Perinatal project to address their hypotheses that lesions associated with maternal vascular malperfusion (MVM) recur in subsequent pregnancies and that this pathology explains the majority of recurrent adverse outcomes (RAO). The methodology is sound and the conclusions largely support previous data that (a) MVM has a significant recurrence risk and (b) MVM is not the only placental pathology associated with RAO, With regard to the latter point, it is well known that other pathologies such as VUE, maternal floor infarction, and chronic histiocytic intervillositis are also associated with RAO and that many RAO do not show any consistent pattern of histopathology. Nevertheless, the data presented with appropriate modifications as detailed below provide a fine grained account of the relationships between different types of RAO, MVM, and decreased placental weight that expand our understanding of this important topic. My more specific comments follow:

1. The MVM broad category is fundamentally flawed. The narrow category combining histologic MVM with decreased placental weight is justified, but there are many other placental histologies associated with decreased placental weight (e.g. VUE, maternal floor infarction, and severe examples of fetal vascular malperfusion and chronic abruption) just as there are many small placentas without any specific histologic changes. I suggest that the MVM broad category be split into two subgroups (1) decreased placental weight NOS and (2) placentas showing histologic MVM with weights greater than 10th percentile. If this decreases the power to find an association, an alternative MVM broad group would be any histologic MVM irrespective of placental weight.

2. Abstract line 36: Shouldn't the word "no" be deleted?

3. Line 152: I do not understand how the last two words "for 3865" apply to this sentence.

4. Lines 158-165 and lines 236-242: These sections address the clinical entity of "recurrent pregnancy loss or miscarriage (3 or more losses)", not the less stringent "previous spontaneous abortion" which would be one or more losses.

5. Lines 263-273: It is not clear whether adjusting for MVM used the narrow or broad definition.

6. Line 316: The term "recurrent placental pathology" is inaccurate. Should be "recurrent MVM" since there are many other placental pathologies, such as VUE, fetal vascular malperfusion, and others, that cause the same outcomes, can recur, and are associated with small placentas.

7. Lines 326-327: Reference 50 addresses recurrent preeclampsia, not adverse outcomes.

8. Lines 332-333: There are actually many papers documenting specific patterns of placental pathology in women with recurrent adverse outcomes ( "multiple complicated pregnancies").

9. Lines 347-351: In this section I actually believe that the authors are underestimating the quality of the original data. I have discussed at length the histopathologic coding of the Collaborative Project with its main study pathologist and I would argue that very little has changed since that time. Differences would be changes in terminology, as the authors discuss, and probably some increased sensitivity for detecting mild lesions. Specifically, I do not think that distal villous hypoplasia would have been missed at that time.

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10 Jan 2020

I have uploaded a "Response to Reviews" file. I have also pasted the text from that file below.

Dear Dr. Spradley,

Thank you very much for the encouraging response to our manuscript (PONE-D-19-32724), and to the reviewer for their constructive comments. Below, we have outlined our responses to each of the comments, with the reviewer’s comments in italics.

Sincerely,

Julian

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We have revised the title page to be consistent with PLOS ONE style. We have also revised the names of the supplementary files, and how they are cited within the manuscript.

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We removed 3 statements with “results not shown”. All three cases stated that similar results were obtained when analyses included institution as a covariate. Since institution does not appear to be an important covariate, we have not included these results.

3. We noticed you have some minor occurrence(s) of overlapping text with the following previous publication(s), which needs to be addressed:

https://doi.org/10.1016/j.placenta.2019.01.012

https://doi.org/10.1177%2F1093526619852871

In your revision ensure you cite all your sources (including your own works), and quote or rephrase any duplicated text outside the Methods section. Further consideration is dependent on these concerns being addressed.

The first publication listed was authored by one of us (JKC) and describes the same dataset, and so there is some overlapping text in the Methods section. In the revised version, we have cited this previous publication at the beginning of the duplicated text.

We have removed the text associated with the second publication. However, we note that in the case the second publication, the overlapping text was due to the description of a number of specific diagnoses and lesions which could not be rephrased, i.e., the repetition of text was not inappropriate. We have confirmed this with Sarah Mills in the Editorial Office.

Review Comments to the Author

Reviewer #1

1. The MVM broad category is fundamentally flawed. The narrow category combining histologic MVM with decreased placental weight is justified, but there are many other placental histologies associated with decreased placental weight (e.g. VUE, maternal floor infarction, and severe examples of fetal vascular malperfusion and chronic abruption) just as there are many small placentas without any specific histologic changes. I suggest that the MVM broad category be split into two subgroups (1) decreased placental weight NOS and (2) placentas showing histologic MVM with weights greater than 10th percentile. If this decreases the power to find an association, an alternative MVM broad group would be any histologic MVM irrespective of placental weight.

We agree with the reviewer’s concerns regarding the broad category. We originally included this category because it was used by a previous publication, and we wanted to allow comparison of different approaches. However, upon reviewing the literature, we can only find one publication using the “broad” approach defined in this way. We have therefore replaced this category with the “alternate” group proposed by the reviewer (i.e., any MVM histology, regardless of placental weight), which is also an approach that has been used previously by others (as cited in revised version). We have not used the subgroups suggested, as the purpose of these analyses is not to compare mutually exclusive groups of pregnancies with each other (low placental weight with no MVM lesion vs. low placental weight with MVM lesion vs. normal placental weight with MVM lesion), but rather to compare different approaches to categorizing MVM lesions that have been used in the literature.

Reanalysis using the new MVM broad category (any MVM lesion, irrespective of placental weight) yields very similar results to our previous MVM broad category, although the prevalence of MVM lesions is somewhat lower (because small placentas with no histological lesions are no longer considered to show MVM lesions).

2. Abstract line 36: Shouldn't the word "no" be deleted?

It has been deleted, thanks.

3. Line 152: I do not understand how the last two words "for 3865" apply to this sentence.

Text has been reworded.

4. Lines 158-165 and lines 236-242: These sections address the clinical entity of "recurrent pregnancy loss or miscarriage (3 or more losses)", not the less stringent "previous spontaneous abortion" which would be one or more losses.

We have used the term “previous spontaneous abortions” rather than “recurrent pregnancy loss” because the latter term is often defined as 3 or more consecutive losses. We only had information on total losses, not consecutive losses.

5. Lines 263-273: It is not clear whether adjusting for MVM used the narrow or broad definition.

This has been clarified.

6. Line 316: The term "recurrent placental pathology" is inaccurate. Should be "recurrent MVM" since there are many other placental pathologies, such as VUE, fetal vascular malperfusion, and others, that cause the same outcomes, can recur, and are associated with small placentas.

Text revised.

7. Lines 326-327: Reference 50 addresses recurrent preeclampsia, not adverse outcomes.

This sentence has been removed (please see response to following comments).

8. Lines 332-333: There are actually many papers documenting specific patterns of placental pathology in women with recurrent adverse outcomes ( "multiple complicated pregnancies").

We agree, and have removed this paragraph. Upon reflection, the references that we cite earlier in the Discussion provide better context for our study than case studies.

9. Lines 347-351: In this section I actually believe that the authors are underestimating the quality of the original data. I have discussed at length the histopathologic coding of the Collaborative Project with its main study pathologist and I would argue that very little has changed since that time. Differences would be changes in terminology, as the authors discuss, and probably some increased sensitivity for detecting mild lesions. Specifically, I do not think that distal villous hypoplasia would have been missed at that time.

We agree regarding the value and quality of the data, and sought to be conservative in considering the limitations of our study. We have moderated this paragraph in response to the reviewer’s comments. The term “distal villous hypoplasia” is not used in the pathology coding of the dataset, and it is not clear what terms in the NCPP dataset would correspond closely to this lesion, but of course during pathological assessment, it may have been noted and described in other terms.

Submitted filename: PLoS ONE Response to Reviews.docx

Click here for additional data file.

15 Jan 2020

PONE-D-19-32724R1

Pregnancy complications recur independently of maternal vascular malperfusion lesions

PLOS ONE

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Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. There are still minor comments raised by the reviewer that need to be addressed. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

We would appreciate receiving your revised manuscript by Feb 29 2020 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Reviewer #1: (No Response)

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Reviewer #1: Yes

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Reviewer #1: Yes

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6. Review Comments to the Author

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Reviewer #1: The authors have substantially improved the manuscript and demonstate that MVM, as defined by 1960's criteria, is not the predominant reason for recurrent adverse outcomes in subjects with MVM in an index pregnancy. Nevertheless, I am not sure that it should be concluded that MVM has no significant recurrence risk. I would make a few points:

1. Why is MVM recurrence risk adjusted for gestational age (GA)? MVM can occur at all gestational ages and there is no a priori reason to assume that GA would be a confounder.

2. Odds ratios are consistently elevated for all comparisons of MVM recurrence in Table 2, adjusted and unadjusted. Recurrence is significant before adjustment for GA in the MVM broad category and borderline significant even after adjustment. The lack of significance for the MVM narrow category might be attributed to small numbers (only 2 subjects with recurrence).

3. There is no a priori reason to restrict recurrence to the previous MVM category. The modifiers are continuous not categorical. In other words, recurrence for MVM narrow should include both broad and narrow MVM and recurrence for MVM broad should include both broad and narrow MVM.

I would ask if the authors might accept that MVM has a recurrence rate, albeit small compared to other factors in explaining subsequent adverse outcomes.

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16 Jan 2020

The comments below are the same as those in the Response to Reviews file that has been uploaded.

Dear Dr. Spradley,

Thanks very much to you and to the reviewer for your prompt response regarding our revised manuscript (PONE-D-19-32724). Below, we have outlined our responses to each of the comments, with the reviewer’s comments in italics.

Sincerely,

Julian

Reviewers' comments:

Reviewer #1: The authors have substantially improved the manuscript and demonstate that MVM, as defined by 1960's criteria, is not the predominant reason for recurrent adverse outcomes in subjects with MVM in an index pregnancy. Nevertheless, I am not sure that it should be concluded that MVM has no significant recurrence risk.

We have modified this conclusion (described further below).

1. Why is MVM recurrence risk adjusted for gestational age (GA)? MVM can occur at all gestational ages and there is no a priori reason to assume that GA would be a confounder.

There are two reasons why gestational age was included in the analysis of recurrence. Firstly, we used the same set of covariates for all analyses for consistency and objectivity, i.e., to avoid analysing the data in different ways and then having to make subjective decisions regarding which analysis to use for each outcome. In the case of MVM, we thought that gestational age might influence the probability of MVM diagnosis (e.g., if some lesions were more apparent later in pregnancy, or if some lesions only develop later in pregnancy). As it turns out, gestational age is a highly significant covariate.

2. Odds ratios are consistently elevated for all comparisons of MVM recurrence in Table 2, adjusted and unadjusted. Recurrence is significant before adjustment for GA in the MVM broad category and borderline significant even after adjustment. The lack of significance for the MVM narrow category might be attributed to small numbers (only 2 subjects with recurrence).

We have revised the text to acknowledge this (in some cases reverting to text in the original manuscript).

3. There is no a priori reason to restrict recurrence to the previous MVM category. The modifiers are continuous not categorical. In other words, recurrence for MVM narrow should include both broad and narrow MVM and recurrence for MVM broad should include both broad and narrow MVM.

The two categories (MVM broad and MVM narrow) are two different criteria for assessing the presence/ absence of the same pathological entity, MVM. We performed analyses with both sets of criteria to allow comparison of these two criteria because some studies have used one approach while others have used the other. Thus, if one believes that MVM narrow provides a better assessment of the presence of MVM, then it wouldn’t make sense to consider the MVM narrow pathology to have recurred if there was MVM broad (but not narrow) in the previous pregnancy and MVM narrow in the subsequent pregnancy. The MVM narrow cases are a subset of the MVM broad cases (i.e., if a pregnancy is categorized as having MVM using the narrow criteria, it will also be so categorized with MVM broad). Therefore, the analysis of recurrence of MVM broad lesions does include MVM narrow lesions in the previous pregnancy.

I would ask if the authors might accept that MVM has a recurrence rate, albeit small compared to other factors in explaining subsequent adverse outcomes.

The revisions in response to comment 2 above acknowledge the recurrence of MVM broad lesions.

Submitted filename: PLoS ONE Response to Reviews 2nd round.docx

Click here for additional data file.

22 Jan 2020

Pregnancy complications recur independently of maternal vascular malperfusion lesions

PONE-D-19-32724R2

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We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

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With kind regards,

Frank T. Spradley

Academic Editor

PLOS ONE

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

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The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

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Reviewer #1: No

27 Jan 2020

PONE-D-19-32724R2

Pregnancy complications recur independently of maternal vascular malperfusion lesions

Dear Dr. Christians:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

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on behalf of

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