Risk factors for obstructed labour in Eastern Uganda: A case control study.

INTRODUCTION: Obstructed labour (OL) is an important clinical and public health problem because of the associated maternal and perinatal morbidity and mortality. Risk factors for OL and its associated obstetric squeal are usually context specific. No epidemiological study has documented the risk factors for OL in Eastern Uganda. This study was conducted to identify the risk factors for OL in Mbale Hospital.
OBJECTIVE: To identify the risk factors for OL in Mbale Regional Referral and Teaching Hospital, Eastern Uganda.
METHODS: We conducted a case control study with 270 cases of women with OL and 270 controls of women without OL. We consecutively enrolled eligible cases between July 2018 and February 2019. For each case, we randomly selected one eligible control admitted in the same 24-hour period. Data was collected using face-to-face interviews and a review of patient notes. Logistic regression was used to identify the risk factors for OL.
RESULTS: The risk factors for OL were, being a referral from a lower health facility (AOR 6.80, 95% CI: 4.20-11.00), prime parity (AOR 2.15 95% CI: 1.26-3.66) and use of herbal medicines in active labour (AOR 2.72 95% CI: 1.49-4.96). Married participants (AOR 0.59 95% CI: 0.35-0.97) with a delivery plan (AOR 0.56 95% CI: 0.35-0.90) and educated partners (AOR 0.57 95% CI: 0.33-0.98) were less likely to have OL. In the adjusted analysis, there was no association between four or more ANC visits and OL, adjusted odds ratio [(AOR) 0.96 95% CI: 0.57-1.63)].
CONCLUSIONS: Prime parity, use of herbal medicines in labour and being a referral from a lower health facility were identified as risk factors. Being married with a delivery plan and an educated partner were protective of OL. Increased frequency of ANC attendance was not protective against obstructed labour.

Introduction

Obstructed labour (OL) occurs when the foetal presenting part fails to descend despite adequate uterine contractions[1]. The global prevalence varies from 2–8%, being highest in low resource settings and almost none existent in high resource settings[1,2]. In Uganda, 8% of all maternal deaths (MDs) and 90% of perinatal deaths due to birth asphyxia are directly attributed to OL[3]. Almost three quarters of the MDs due to primary postpartum haemorrhage(PPH) and sepsis have OL as an underlying cause[4,5]. Limited or no access to quality emergency obstetric care services in low resource settings contributes to the high number of adverse obstetric outcomes[6].

Prevention of OL requires a multidisciplinary approach aimed in the short term at identifying high risk cases. In the long term,improving incomes at the level of the household would promote access to better nutrition, education and healthcare for the girl child [1,7]. Current evidence shows that access to skilled care during pregnancy and childbirth can mitigate adverse maternal and perinatal outcomes associated with OL[8]. In this regard, risk profiling during antenatal care (ANC) and intrapartum maternal fetal surveillance using a partogram are key interventions for early detection and management.

In Uganda, the utilisation of maternity services has improved with more than 90% for the first ANC visit, 60% for at least four ANC visits and facility births are at 73%[9]. Unfortunately, these improvements have not translated into a significant reduction in morbidity and mortality[9]. In addition, the known risk factors for OL have a poor predictive value that makes primary prevention difficult[10-12]. Parity, place of residence and age were significantly associated with OL after a review of patient records in six health facilities of western Uganda [2]. In Mbale Hospital, anecdotal evidence suggests that OL is the most common indication for primary emergency caesarean section and a cause of significant morbidity and mortality. The risk factors for OL and its associated obstetric sequel are usually context specific[13]. Currently, no epidemiological study has documented the risk factors for OL in Eastern Uganda. This study identified the risk factors for OL in Mbale Regional Referral and Teaching Hospital, Eastern Uganda. We hypothesised that increased frequency of ANC attendance (<4 versus ≥ 4 visits) was protective of OL.

Materials and methods

Study setting

We conducted this study in the labour suite of Mbale regional referral Hospital in Eastern Uganda. This hospital, serves 14 districts in the Elgon zone with an estimated population of 4 million people. This is a government run, not-for-profit, charge-free, 470-bed hospital with 52 maternity beds. Annually, about 12,000 childbirths occur in this hospital with a caesarean section rate of 35% and nearly 500 mothers have OL. About two thirds of these mothers with OL are referrals in active labour from the lower health units.

Study design

Unmatched case control design with incidence density sampling of the controls admitted in the same delivery suite.

Study population

All patients admitted to the labour suite in active labour at term (≥ 37 weeks of gestation) were screened. A Medical Officer or Obstetrician diagnosed OL using the American College of Obstetricians and Gynecologists (ACOG) guideline for arrest of labour [14] and local protocols. A case was defined as; a cervical dilatation ≥ 6cm with ruptured membranes, having adequate contractions lasting > 4hrs with no change in cervical dilatation in the first stage of labour. For the second active stage of labour, arrest was defined as a delay of > 2 hours for the nullipara and > 1 hour for the multipara with adequate uterine contractions. In addition, a case had to have any two of the following obvious signs of severe obstruction: caput formation, Bandl’s ring, sub-conjunctival hemorrhages and edematous vulva.

Controls were women admitted to the labour suit within the same 24-hour period in active labour without obstruction.

Sample size and sampling

We used the formula described by Fleiss with a continuity correction to estimate the sample size[15]. The exposure factor was the proportion of pregnant women who attended < 4 ANC visits. We enrolled 270 cases and 270 controls based on the following assumptions: two-sided 95% confidence level, power of 95%, ratio 1:1 to detect an odds ratio of at least 2 for the risk of OL among pregnant women who attended < 4 ANC visits as the main exposure variable[16-18]. We further assumed that controls were like any other pregnant woman in Uganda who attended at least 4 ANC visits (60%) according to the Uganda demographic and health survey [9].

We consecutively enrolled all eligible incident cases between July 2018 and February 2019. We used simple random sampling to select one control from a list of admissions in active labour immediately after enrolling each case. Before recruitment, all respondents gave us written informed consent and pregnant adolescents below the legal age of 18 years were taken as emancipated minors[19]. We used unique study numbers issued at enrolment to identify each respondent.

Inclusion criteria

Cases were women with OL carrying singleton, term pregnancies in cephalic presentation. Controls were women in active labour without obstruction carrying singleton, term pregnancies in cephalic presentation.

Exclusion criteria

We excluded women with other obstetric emergencies such as antepartum haemorrhage, Pre-eclampsia and eclampsia (defined as elevated blood pressure of at least 140/90 mmHg, urine protein of at least 2+, any of the danger signs and fits), premature rupture of membranes and intrauterine fetal death. We also excluded all women from outside the Hospital catchment area of 14 districts as either cases or controls.

Study variables

The socio-demographic factors highlighted in the literature to predispose women to OL were the participant’s age, marital status, occupation, level of education, the occupation and education level of the spouse as well as distance to the nearest health facility and the place of residence[10,12,17,20,21]. The obstetric factors were gravidity, number of ANC visits, having a delivery plan in place, a history of being referred from a lower health facility and use of herbal medications during labour[16,17]. Physical examination included the respondent’s height and fetal birth weight. Our main exposure was the number of ANC visits attended as indicated on the ANC card, the other covariates were considered as confounders.

Data collection

We used an interviewer-administered questionnaire running on an open data kit (ODK) platform. Trained research assistants (RA’s) who are qualified midwives administered the questionnaire to all participants in the local dialect. We blinded all the RA’s to the hypothesis of the study. Available records such as the antenatal cards, facility registers and case report files were reviewed by the RA’s to crosscheck some of the verbal responses. The principal investigator (PI) would, on a daily basis access and review the data from the Google Aggregate server for completeness.

Data management

The data was uploaded to a password protected server to which only the PI or his designee had access. Assisted by a statistician, the data was downloaded into an excel spreadsheet and exported to Stata version 14 for further cleaning and analysis.

Data analysis

Baseline socio-demographic, physical and obstetric characteristics of the cases and controls were compared, to identify any differences. Normality of the continuous variables was tested for using the Shapiro-Wilk test. We summarised continuous variables using means and standard deviations. Whereas frequencies and percentages were used for the categorical variables. We used logistic regression (LR) to estimate Odds ratios, and 95% confidence intervals to examine the association between the number of ANC visits (< 4 Vs ≥ 4) and the different socio-demographic, physical and obstetric covariates in bivariable and multivariable analysis. We included all factors that are known to confound the relationship between the frequency of ANC attendance and OL in the multivariable LR model, based on biological plausibility. In order to control for potential residual confounding due to factors that we had not previously hypothesized to be confounders, we also included those variables for which bivariable analysis returned a p-value equal to or less than 0.25. We reasoned that a cut-off of 0.25 would allow us to test the effect of any factors previously not known to have a confounding effect on the relationship between OL and the frequency of ANC attendance, without including those factors that were reasonably least likely [22]. Multicollinearity between explanatory variables was assessed using the variance inflation factor (VIFs), and they were all less than 1.5.

In the final adjusted multivariable model, we included all the statistically significant covariates (being a referral, a history of using herbal medicines, having a delivery plan, prime parity and partner education level). Confounding was considered present, if the difference between the crude and adjusted OR was ≥ 10 percentage points[23,24].

Ethical considerations

The Makerere University School of Medicine Research and Ethics Committee (#REC REF 2017–103) and the Uganda National Council for Science and Technology (HS217ES) approved the protocol. The Mbale Hospital Research and Ethics Committee (MRRH-REC IN-COM 00/2018) gave us administrative clearance. The hospital protocols were followed in management emergencies during the study.

Results

Characteristics of the study population

The respondents were generally young with a mean age of 24.5± 6 years, of average stature with a mean height of 160±8.2 cm and gave birth to babies of normal birth weight with a mean of 3.3± 0.4 Kg. Almost all (99%) respondents attended at least one ANC visit, mostly (96%) in public health facilities. Two-thirds (68%) of the respondents had no delivery plan in place. Majority of respondents resided in rural areas (84%) with no formal employment (89%) and almost one-half (44%) had used herbal medications during labour. The cases were younger (mean age 23.5±5.9 Vs 25.4±5.9), P-value <0.001 and shorter (159±8.2 Vs 161.4±7.4), P-value 0.011 than the controls (Table 1).

Table 1

Baseline characteristics of the participants.

Characteristic	Cases	Controls	Total
	n = 270 (100%)	n = 270 (100%)	N = 540 (100%)
Age, years (SD)*	23.5 (5.9)	25.4 (5.9)	24.5 (6.0)
less than 20	80 (29.6)	42 (15.6)	122 (22.6)
20 to 29	147 (54.4)	165 (61.1)	312 (57.8)
30 and above	43 (15.9)	63 (23.3)	106 (19.6)
Mean height, cm (SD)*	159 (8.2)	161 (7.4)	160 (8.2)
less than 150	46 (17.0)	22 (8.2)	68 (12.6)
150 and above	224 (83.0)	248 (91.9)	472 (87.4)
Mean weight, kg (SD)*	64.1 (10.1)	65.3 (9.3)	64.7 (9.8)
Mean fetal birth weight, kg (SD)*	3.30 (0.5)	3.36 (0.4)	3.33 (0.4)
less than 2.5	6 (2.2)	2 (0.7)	8 (1.5)
2.5 to 3.5	166 (61.4)	134 (49.6)	300 (55.6)
>3.5	98 (36.3)	134 (49.6)	232 (43.0)
Mean fetal heart rate, bpm (SD)*	138 (13.7)	136 (8.4)	136 (15.2)
less than 120	15 (5.6)	2 (0.7)	17 (3.2)
120 to 160	240 (88.9)	264 (97.8)	504 (93.3)
above 160	15 (5.6)	4(1.5)	19 (3.5)
Marital status
Not Married	46 (17)	29 (10.7)	75 (13.9)
Married	224 (83.0)	241 (89.3)	465 (86.1)
Education level of respondent
Primary	139 (51.5)	99 (36.7)	238 (44.1)
Post primary	131 (48.5)	171 (63.3)	302 (55.9)
Occupation of respondent
House wife	176 (65)	164 (61)	340(63)
Peasant farmer	40 (15)	21 (8)	61 (11)
Salary earner	31 (12)	28 (10)	59 (11)
Retail business	23 (9)	57 (21)	80 (15)
Place of Residence
Rural	239 (89)	212 (79)	451 (84)
Urban	31 (12)	58 (22)	89 (17)
Distance to the nearest Health Unit
< 5 km	205 (75.9)	221 (81.8)	426 (78.9)
≥ 5 km	65 (24.1)	49 (18.2)	114 (21.1)
Education level of spouse
Primary	126 (46.7)	74 (27.4)	200 (37)
Post primary	144 (53.3)	196 (72.6)	340 (63)
Occupation of spouse
Peasant farmer	177 (65.6)	143 (53)	320(59.3)
Retail business	44 (16.3)	58 (21.5)	102(18.9)
Income earner	49 (18.2)	69 (25.6)	118(21.9)
Gravidity
Prime gravida	150 (55.6)	79 (29.3)	229 (42.4)
Gravida 2 to 4	85 (31.5)	151 (55.9)	236 (43.7)
Gravida 5+	35 (13.0)	40 (14.8)	75 (13.9)
Number of ANC visits
< 4 ANC visits	153 (56.7)	152 (56.5)	305 (56.6)
≥ 4 ANC visits	117 (43.3)	118 (43.5)	234 (43.4)
Health facility attended for ANC
Public health facility	261 (96.7)	258 (95.5)	518 (96.1)
Private health facility	9 (3.3)	12 (4.5)	21 (3.9)
Have a delivery plan in place
Yes	79 (29.3)	93 (34.6)	172 (31.9)
No	191 (70.7)	177 (65.4)	368 (68.1)
Used herbal medicines in labour
Yes	161 (59.6)	79 (29.3)	240 (44.4)
No	109 (40.4)	171 (70.7)	300 (55.6)
Being a referral
Yes	184 (68.2)	45 (16.7)	229 (42.4)
No	86 (31.9)	225 (83.3)	311 (57.6)
Source of referral
Public health facility	174 (95)	40 (89)	214 (94)
Private health facility	10 (5.4)	5 (11.1)	15 (6.5)

Abbreviations: cm, centimetre; km, kilometre; kg, kilogram; bpm, beats per minute; ANC, antenatal care; SD, standard deviation.

* Values are given as mean ±SD or number (percentages) unless stated otherwise

Factors associated with OL

Maternal age, height, marital status, level of education, occupation and place of residence as well as the spouse’s level of education and occupation were associated with OL. Obstetric factors such as prime parity, presence of an abnormal fetal heart rate, use of herbal medications in labour and history of being referred were associated with OL.

The odds of obstructed labour among referred women were 10 [crude odds ratio (COR) 9.69: 95% CI 5.79–16.21)] times the odds of obstructed labour among the women not referred. We found no association between OL and the number of ANC visits (COR 1.01, 95% CI: 0.73–1.41). The fetal birth weight among cases was 3.30±0.45 and 3.36±0.41 among controls and was not associated with OL. The odds of obstructed labour among married women was 0.6 times (COR 0.59 (0.35–0.97) the odds of obstructed labour among unmarried women (Table 2).

Table 2

Factors associated with obstructed labour at bivariable analysis.

Characteristic	Crude OR	95% CI	P- Value
Mean age, years (SD)*	-0.05	-0.08 - -0.03	0.000
less than 20	2.14	1.38–3.30	0.001
20 to 29	1
30 and above	0.77	0.49–1.20	0.243
Mean height, cm (SD)*	-0.03	-0.05 - -0.01	0.011
less than 150	1.78	0.83–3.82	0.137
above 150	1
Mean weight, kg (SD)*	-0.01	-0.03 - -0.00	0.142
Mean fetal birth weight, kg (SD)*	-0.34	-0.74 - -0.05	0.088
less than 2.5	2.42	0.48–12.19	0.284
2.5 to 3.5	1
above 3.5	0.59	0.42–0.83	0.003
Mean fetal heart rate, bpm (SD)*	-0.02	-0.00 - -0.03	0.040
less than 120	14.24	1.85–109.6	0.011
120 to 160	1
above 160	4.11	1.34–12.54	0.013
Marital status
Married	0.59	0.35–0.97	0.037
Not Married	1
Education level of respondent
Post primary	0.55	0.39–0.67	0.001
Primary	1
Occupation of respondent
House wife	1
Peasant farmer	1.77	1.00–3.14	0.048
Salary earner	1.03	0.59–1.79	0.912
Retail business	0.38	0.22–0.64	0.000
Place of Residence
Rural	0.48	0.30–0.77	0.003
Urban	1
Distance to the nearest Health Unit
≥ 5 km	1.43	0.94–2.18	0.093
<5 km	1
Education level of spouse
Primary	0.43	0.30–0.62	0.000
Post primary	1
Occupation of spouse
Peasant farmer	1
Retail business	0.61	0.39–0.96	0.033
Paid employee	0.57	0.37–0.88	0.011
Gravidity
Prime gravida	3.37	2.31–4.94	0.000
Gravida 2 to 4	1
Gravida 5+	1.55	0.92–2.63	0.100
Number of ANC visits
< 4 ANC visits	1.01	0.73–1.41	0.933
≥ 4 ANC visits	1
Health facility attended for ANC
Public health facility	1.38	0.55–3.42	0.493
Private health facility	1
Have a delivery plan
Yes	0.79	0.55–1.13	0.196
No	1
Used herbal medicines in labour
Yes	3.65	2.45–5.42	0.000
No	1
Being a referral
Yes	9.69	5.79–16.21	0.000
No	1
Source of referral
Public health facility	1.00	0.20–4.96	1.000
Private health facility	1

Abbreviations: cm, centimetre; km, kilometre; kg, kilogram; bpm, beats per minute; ANC, antenatal care; SD, standard deviation; CI, confidence interval.

* logit coefficients.

After adjusting for confounding (Table 3), these factors were independently associated with OL: having a partner with post primary education (AOR 0.57 95% CI: 0.33–0.98), being a referral from a lower health facility (AOR 6.80, 95% CI: 4.20–11.00), prime parity (AOR 2.15 95% CI: 1.26–3.66), use of herbal medicines in labour (AOR 2.43 95% CI: 1.50–3.64), having a delivery plan (AOR 0.56 95% CI: 0.35–0.90) and a fetal heart rate < 120 beats per minute (AOR 10.78 95% CI: 1.21–96.11).

Table 3

Risk factors independently associated with obstructed labour.

Characteristic	Adjusted OR	95% CI	P- Value
Maternal age, years
less than 20	0.9	0.48–1.70	0.747
20 to 29	1
30 and above	0.93	0.47–1.82	0.822
Maternal height, cm
above 150	1
Less than 150	1.08	0.41–2.86	0.875
Fetal heart rate, bpm
less than 120	10.78	1.21–96.11	0.033
120 to 160	1
above 160	2.37	0.62–9.01	0.205
Fetal birth weight, kg
less than 2.5	1.95	0.23–16.71	0.541
2.5 to 3.5	1
above 3.5	0.95	0.606–1.49	0.818
Marital status
Not Married	1
Married	0.92	0.47–1.78	0.796
Education level of respondent
Post Primary	0.65	0.38–1.13	0.127
Primary	1
Occupation of respondent
House wife	1
Peasant farmer	1.25	0.56–2.76	0.341
Salaried	1.50	0.68–3.31	0.318
Retail business	0.80	0.42–1.55	0.514
Place of Residence
Rural	1.77	0.89–3.54	0.104
Urban	1
Distance to the nearest Health Unit
≥ 5 km	0.94	0.45–1.97	0.870
<5 km	1
Education level of spouse
Post Primary	0.57	0.33–0.98	0.042
Primary	1
Occupation of spouse
Peasant farmer	1
Retail business	1.44	0.73–2.84	0.291
Paid employee	1.19	0.68–2.10	0.537
Gravidity
Prime gravida	2.15	1.26–3.66	0.005
Gravida 2 to 4	1
Gravida 5+	0.80	0.36–1.748	0.573
Number of ANC visits
< 4 ANC visits	0.95	0.61–1.48	0.821
≥ 4 ANC visits	1
Have a delivery plan in place
Yes	0.56	0.35–0.90	0.017
No	1
Used herbal medicines in labour
Yes	2.34	1.50–3.64	0.000
No	1
Being a referral
Yes	6.80	4.20–11.00	0.000
No	1

Abbreviations: cm, centimetre; km, kilometre; kg, kilogram; bpm, beats per minute; ANC, antenatal care; SD, standard deviation; CI, confidence interval.

Discussion

We conducted a case control study using incidence density sampling to identify risk factors for OL in Mbale Hospital. We found that increased frequency of ANC attendance (< 4 Vs ≥ 4 ANC visits) was not protective against OL, contrary to our postulation. The risk factors for obstructed labour were prime parity, use of herbal medicines in labour, being a referral from a lower health facility, as well as having a low fetal heart rate (<120 beats per minute) at enrolment. Having a delivery plan in place, an educated male partner and being married were protective of OL.

In this study, almost all the participants attended at least one ANC visit, which made the cases and controls similar on this particular characteristic. For instance, 43.3% of the cases and 43.5% of the controls attended four or more ANC visits. Despite this high level of utilisation of ANC services in mostly government public health facilities, being a referral from a lower health facility in active labour was independently associated with OL, implying that the quality of care at the lower health facilities may be substandard[25]. This could be attributed to the existing mismatch between the low staffing levels and high patient turnover that is common at public health facilities in Uganda[25,26]. Therefore, it is not surprising that OL was not associated with the frequency of ANC attendance in the current study. In a case control study among obstetric fistula patients in western Uganda, Barageine et al found no association between ANC attendance and obstetric fistula (a direct consequence of prolonged OL) [13]. On the contrary, several descriptive studies done in Nigeria and Ethiopia have found none utilisation of ANC services to be associated with OL[27,28]. It is likely that the effect of increased frequency ANC on OL is small and therefore another study with lager sample to study the effect of timing and number of individual ANC visits on OL, since it is known that frequent ANC visits especially in the last trimester prevents adverse obstetric outcomes[29]. The occurrence of OL and its squeal is influenced by delays due to a none functional referral system such as duration of labour before arrival to a health facility and taking > 4 hours to travel to a health facility for care [12,30,31]. The current study did not investigate the delays associated with OL, which was a limitation. Nonetheless, our finding of the odds of obstructed labour among referred women being seven times the odds of obstructed labour among non-referred has important implications because OL is an emergency that needs to be relieved in its early stages to prevent the associated morbidity and mortality. For public health, it may be a pointer to the lack of capacity to manage abnormal labour at district level hospitals and county level health centre IV’s to offer emergency obstetric services closer to the community as it was envisioned in the governments’ decentralisation plan[32]. Most of the patients were sent without clear documentation and specific diagnosis of obstructed labour. Sixty percent of the women with OL had used herbal medications in labour compared to 29% of the controls. Very often, when labour is not progressing well there is a high tendency to use local herbs in an attempt to quicken the process[33,34]. Referral to larger health facility is usually a last resort when everything else has failed[35]. So, it is not surprising that the odds of OL were two times higher among women with a positive history of having used herbal medications compared to those with a negative history.

The odds of obstructed labour were two times higher among the prime paras compared to the multiparous women in our study. Several studies have reported similar findings [2,12,36]. In our setting, many first time mothers are also young and it is possible that a link exists between prime parity and maternal age[2,11,12]. Although the current study was not powered to study this relationship, we know that young girls are prone to OL because they have an under developed pelvic cavity [2,13,37]. In addition, they have limited access to quality maternity services due to social and economic disadvantages and the fact that they usually conceive outside formal marriage. A prospective study involving only teenagers or prime paras would be necessary to resolve this contradiction.

Contrary to findings from similar low resource settings, the participants height, education level, occupation, distance to the nearest health facility with emergency obstetric care services and the occupation of the spouse were not identified as risk factors for OL [2,10-13,36]. Although, having an educated spouse (at least post primary level) and a delivery plan in place was protective of OL. Our findings are in agreement with the thinking that the known risk factors for OL have a poor predictive value, which makes primary prevention difficult[2,10,12,36]. This underscores the importance of having each child birth supervised by a skilled birth attendant. Although, the discrepancy might also be because we adopted an analytical approach to identify independent risk factors, while the earlier studies were mostly descriptive in nature to identify associated factors.

Fetal size was not a risk factor for OL. It is known that carrying a big baby (> 4kg) is a risk factor for OL because it increases the likelihood of cephalopelvic disproportion which is a common cause of OL [12,13]. In this study, the mean fetal birth weight was 3.33 kg and there was no significant difference between cases and controls on this characteristic. Ndibazza et al reported a mean fetal birth weight of 3.17 kg among 2,507 pregnant women recruited in a clinical trial in central Uganda [25], which is similar to our findings. In addition, most of the participants in this study were small with a mean body weight of 62 kg and no significant differences between cases and controls.

Post hoc power calculations suggest that our study may have been underpowered to detect a clinically important difference between the frequency of antenatal care visits (< 4 Vs ≥ 4 ANC visits) and OL even if the difference had been there (S1 File). For now, our results need to be interpreted with caution until they are validated by larger studies powered to detect small differences. However, conducting post hoc power calculations of this type may not be helpful as this can easily be seen from the confidence intervals that show an imprecise estimate and there is a huge body of statistical evidence that calculating a post hoc power is logically flawed (S3 File).

Methodological considerations

In this study, we used incidence density sampling to identify controls. This strategy helped us to minimise selection bias but we could not assess the effect of time/ duration that has been highlighted as a risk factor in several other studies[12].

The RA’s were well trained and blinded to the main hypothesis of the study to minimise information bias arising from paying more attention to the cases during the interviews. We triangulated the sources of information by supplementing the verbal responses with a review of the participant’s case notes.

In this hospital-based study, most of the patients were referrals so the findings might not be a true representation of the picture in the Elgon sub-region. It would be interesting to compare the referred cases with controls selected from the same referring health facility, which was beyond the scope of this study. These results may be generalizable to other regional referral hospitals in Uganda because the health care delivery system is uniformly organised across the country.

Conclusion

Prime parity, being a referral and history of using herbal medicines in labour were identified as risk factors for OL. On the other hand, having a delivery plan in place and an educated partner (at least post primary level) were found to be protective of OL. We found no association between the frequency of ANC attendance and the risk of OL.

Post hoc power calculations.

(DOCX)

Click here for additional data file.

Dataset RFOLMUK.

The data set is in Stata format 14 and includes all variables analysed for this manuscript.

(DTA)

Click here for additional data file.

Post hoc power calculations rebuttal.

(DOCX)

Click here for additional data file.

20 Nov 2019

Submitted filename: response to the reviewers.docx

Click here for additional data file.

2 Jan 2020

PONE-D-19-32285

Risk factors for obstructed labour in Eastern Uganda: a case control study.

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An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

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We look forward to receiving your revised manuscript.

Kind regards,

Calistus Wilunda, DrPH

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

Please include post hoc power calculations to show the extent to which the study was powered to examine the link between the factors assessed and obstructed labour. This is in the light of the fact that this study was not well powered to assess the link between ANC attendance and the outcome. You can include this information as a supplementary file.

Journal Requirements:

When submitting your revision, we need you to address these additional requirements:

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at http://www.plosone.org/attachments/PLOSOne_formatting_sample_main_body.pdf and http://www.plosone.org/attachments/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions.

In your revised cover letter, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories.

We will update your Data Availability statement on your behalf to reflect the information you provide.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. 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

Reviewer #2: Partly

**********

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

Reviewer #1: Yes

Reviewer #2: I Don't Know

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

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: No

Reviewer #2: Yes

**********

4. 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: No

Reviewer #2: Yes

**********

5. 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: In this study, the authors conducted a case-control study to explore the risk factors for obstructed labour (OL) in Eastern Uganda. This study is of great public health importance. Overall, the study was well planned and conducted, analysis was correctly performed, results carefully discussed and manuscript nicely written. The authors also addressed the study limitations. Several issues:

1) The full name of an abbreviation should be given at the first appearance. For example, Introduction section, 1st paragraph, Line 63, “PPH”.

2) Introduction, 2nd paragraph, Line 67, what do you mean by “improving nutrition of the girl child…?”

3) Results section, 1st paragraph, Line 199, “159±8.2 Vs 1161.4±7.4”, please check height is correctly presented.

4) The result for the main hypothesis is negative. There is the issue of multiple comparisons, so the conclusions should be drawn with caution.

5) The presentations of Table 2 and Table 3 should be improved. The reference category usually should be consistent, either at the top or at the bottom.

6) Typos and grammatical errors need to be checked and corrected.

Reviewer #2: While the study presents the results of original research, the statistics and other analyses still need to be described in more sufficient detail to know whether they were performed to a high technical standard. The conclusions need to be presented in a more robust fashion and provide more explanation of what the data support and results show.

Even though the article is presented is written in standard English, it could be improved with additional copy-editing for correct grammar usage. Revisions would be easier to track if authors had highlighted or underlined changes in the text.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (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. Registration is free. 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 figures@plos.org. Please note that Supporting Information files do not need this step.

20 Jan 2020

20th/01/2020

To

Dr. Calistus Wilunda

Academic Editor

PLOS ONE

Dear Dr. Calistus Wilunda

Re; Response to reviewers’ comments and resubmission of revised manuscript ID PONE-D-19-20983

Thank you for taking off time to review and provide feedback on this manuscript. Please receive the revised copy with specific responses and changes summarized in the table below.

Reviewers comment Response to comment Line number

Academic editor

Please include post hoc power calculations to show the extent to which the study was powered to examine the link between the factors assessed and obstructed labour. This is in the light of the fact that this study was not well powered to assess the link between ANC attendance and the outcome. You can include this information as a supplementary file. Thank you so much for the comment. We agree with the reviewer that most likely we did not have power to detect a difference between the frequency of antenatal care visits (< 4 Vs ≥ 4 ANC visits) and obstructed labour even if the difference had been there. This can easily be seen from the confidence intervals that show an imprecise estimate. The post hoc power calculations have been done for all the variables studied; referral status, use of local herbs, having a delivery plan, number of ANC visits, prime parity, occupation of the spouse, education level of spouse, distance from the nearest health facility, place of residence, occupation of the spouse, participants level of education, marital status, fetal birth weight and height of respondent.

We however agree with a huge body of statistical evidence that calculating a post hoc power is logically flawed for the reasons highlighted in supplement 3

Included as a separate file name post hoc power calculations (S1).

Lines 284 to 289, page 17.

Included as a separate file Post hoc power calculations rebuttal (S3)

Journal Requirements:

Comment 1;

Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. We have updated all these accordingly and feel that the manuscript meets PLOS ONE’s style requirements. NA

Comment 2.

We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly.

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Thank you for the guidance, after consultations with the sponsor of the study and the Makerere University School of Medicine Research and Ethics Committee (SOMREC), we have uploaded the minimal anonymized data set necessary to replicate study findings as Supporting Information file (S2 file. Dataset RFOLMUK) NA

Reviewer 1

Comment.

In this study, the authors conducted a case-control study to explore the risk factors for obstructed labour (OL) in Eastern Uganda. This study is of great public health importance. Overall, the study was well planned and conducted, analysis was correctly performed, results carefully discussed and manuscript nicely written. The authors also addressed the study limitations. Several issues: Thank you for the feedback. NA

Issue1;

The full name of an abbreviation should be given at the first appearance. For example, Introduction section, 1st paragraph, Line 63, “PPH”. Thank you for the observation, this has been written out in full as postpartum hemorrhage. Line 56, page 4.

Issue 2;

Introduction, 2nd paragraph, Line 67, what do you mean by “improving nutrition of the girl child…?” This has been elaborated further in the manuscript Lines 61-63, page 4.

Issue 3;

Results section, 1st paragraph, Line 199, “159±8.2 Vs 1161.4±7.4”, please check height is correctly presented. Thank you for the observation, this has been corrected in the manuscript to “159±8.2 Vs 161.4±7.4”, Line 183, page 9.

Issue 4;

The result for the main hypothesis is negative. There is the issue of multiple comparisons, so the conclusions should be drawn with caution. This limitation has been highlighted in the discussion section Line 233 to 236, page 15

Issue 5;

The presentations of Table 2 and Table 3 should be improved. The reference category usually should be consistent, either at the top or at the bottom. All the tables have been reviewed and revised Table 1: Line 185 to186, page 9 to 11

Table2: Line 200 to201, page 11 to 12

Table 3: Line 209 to 210, page 13 to 14.

Issue 6;

Typos and grammatical errors need to be checked and corrected. These have been checked and corrected throughout the document NA

Reviewer 2;

Comment 1.

While the study presents the results of original research, the statistics and other analyses still need to be described in more sufficient detail to know whether they were performed to a high technical standard. The conclusions need to be presented in a more robust fashion and provide more explanation of what the data support and results show. The statistical analysis has been described in more detail and the data set is attached.

We have also added a post hoc power calculation.

Discussed the power limitations in more detail

Line 150 to 171, page 8 and 9.

Supplement file S1.

Lines 284 to 289, page 17.

Comment 2.

Even though the article is presented is written in standard English, it could be improved with additional copy-editing for correct grammar usage. This has been done throughout the document NA

Comment 3.

Revisions would be easier to track if authors had highlighted or underlined changes in the text Sorry for the inconvenience, we have included a revised copy of the manuscript with track changes. Throughout the document.

END

Sincerely,

Dr. Musaba W. Milton

Department of Obstetrics and Gynaecology

Mbale Regional Referral Hospital/ Busitema University

Submitted filename: response to the reviewers2.docx

Click here for additional data file.

27 Jan 2020

Risk factors for obstructed labour in Eastern Uganda: a case control study.

PONE-D-19-32285R1

Dear Dr. Musaba,

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.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, you must inform our press team as soon as possible and no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

With kind regards,

Calistus Wilunda, DrPH

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

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

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

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: The authors have addressed all my concerns after the revision.

I suggest accept the manuscript for publication.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

30 Jan 2020

PONE-D-19-32285R1

Risk factors for obstructed labour in Eastern Uganda: a case control study.

Dear Dr. Musaba:

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.

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. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

For any other questions or concerns, please email plosone@plos.org.

Thank you for submitting your work to PLOS ONE.

With kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Calistus Wilunda

Academic Editor

PLOS ONE