SUDANESE JOURNAL OF PAEDIATRICS

2020; Vol 20, Issue No. 2

ORIGINAL ARTICLE

Risk factors associated with preterm birth: a retrospective study in Mukalla Maternity and Childhood Hospital, Hadhramout Coast/Yemen

Haifa Ali Bin Dahman (1)

(1) Associate Professor of Pediatrics, Pediatric Department, Hadhramout University, College of Medicine, Hadhramout Governorate, Yemen

Correspondence to:

Haifa Ali Bin Dahman

Associate Professor of Pediatrics, Pediatric Department, Hadhramout University, College of Medicine, Hadhramout Governorate, Yemen.

Email: Bin_Dahman.H [at] hotmail.com

Received: 07 December 2019 | Accepted: 25 May 2020

How to cite this article:

Bin Dahman HA. Risk factors associated with preterm birth: a retrospective study in Mukalla Maternity and Childhood Hospital, Hadhramout Coast, Yemen. Sudan J Paediatr. 2020;20(2):99–110.

https://doi.org/10.24911/SJP.106-1575722503

ABSTRACT

Preterm birth (PTB) is a major determinant of neonatal mortality, morbidity and childhood disability. It has long-term adverse consequences for health. The causes of preterm delivery (PTD) are multifactorial. This study was conducted to determine the most common risk factors for PTB at Mukalla Maternity and Childhood (MCH) Hospital, Yemen. A retrospective case-control study was conducted. It involved the records of 100 women with live PTD as cases and 400 women with live term delivery as controls at Mukalla MCH Hospital in 2018. All the data were analysed using the Statistical Package for the Social Sciences (version 24). The statistical relationship between independent variables and PTB was studied by the Chi-square test in bivariate analysis and logistic regression in multivariate analysis. The strength of association was confirmed by using odds ratios (ORs) with a 95% confidence interval (CI). Risk factors with statistically significant association with premature birth were a family history of PTD (adjusted OR [AOR] 2.353; CI 1.3-4.258, p-value 0.005), pre-eclampsia (AOR 4.120; CI 1.818-9.340, p-value 0.001), parity (AOR 2.139; CI 1.249-3.662, p-value 0.006), premature rupture of membranes (AOR 4.161; CI 2.323-7.456, p-value 0.000) and abnormal amniotic fluid volume (AOR 4.534; CI 1.364-15.071, p-value 0.014). An early recognition of preterm risk factors will help medical staff and healthcare workers to identify women with a high-risk pregnancy.

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KEYWORDS

Premature; Preterm; Premature rupture of membranes; Hypertension; Risk factor; Mukalla; Yemen.

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INTRODUCTION

The World Health Organisation (WHO) defined the premature birth or preterm birth (PTB) as birth occurring after 20 weeks and before 37 weeks of gestation [1]. It can be further subdivided into 5% extremely preterm (<28 weeks), 10% very preterm (28-<32 weeks) and 85% moderate preterm (32-<37 completed weeks of gestation) [2–5].

PTB is a major public health issue and the most important clinical problem in obstetrics and neonatal medicine [2]. It is considered as the leading cause of high perinatal and postnatal morbidity and mortality in the developed and developing countries [6–10]. Each year, 15 million premature babies are born in the world. Preterm complications are responsible for death in approximately 1 million preterm babies yearly [3]. Prematurity is the second cause of infant deaths after congenital abnormalities [11].

PTB rates varied widely between countries [12] with higher incidences in developing countries than in developed countries [8,12]. At a national level, the estimated PTB rate ranged from about 5%-18%; the highest rates of PTB were in Southeastern Asia and Sub-Saharan Africa (13.5% and 12.3% of all live births, respectively) [12]. An increment of 21% in PTB rates was reported in the United States in comparison to the 1990s [13].

Cerebral palsy, sensory deficit, learning disabilities and respiratory illnesses occur more frequently amongst children born with prematurity [2,4,14]. The morbidity associated with PTB results in enormous physical, psychological and economic costs in later life [15]. Moreover, PTB carries both a financial and social burden on their families. This is related to the expenses from providing intensive care for extremely preterm newborns [13,16,17], prolonged hospital stay and sudden loss of preterm babies [2].

PTB aetiology is incompletely understood. It is thought to involve various obstetric, genetic, environmental and demographic factors that may act independently or interact to cause PTB [8]. The risk of PTB is increased when a combination of two or more factors is present [18].

Most of the risk factors for PTB are modifiable [19]. More than 75% of PTB deaths can be prevented without intensive care [2]. Over the past decade, seven countries have halved their deaths due to PTB by ensuring that the frontline workers are skilled in the care of premature babies and improving supplies of life-saving commodities and equipment [2]. Despite the advances in prenatal medicine and preterm preventive measures, other countries showed an increment in PTB incidence with related morbidity and mortality [20]. The objective of this study was to determine the most common risk factors contributing to preterm deliveries at Mukalla Maternity and Childhood (MCH) Hospital, Yemen.

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MATERIALS AND METHODS

The study was designed as a retrospective case-control (1:4) study at Mukalla MCH Hospital, Hadhramout Coast, Yemen, during January-May 2018. The records of 591 live-born deliveries in the Gynaecology and Obstetrics Ward, Mukalla MCH Hospital, were divided into two groups. One of these was a case group (mothers with preterm delivery [PTD] and their infants) consisting of 100 preterm deliveries by vaginal delivery or caesarean section (CS), out of a total of 107 preterm deliveries during the study period. Here, seven medical records were excluded due to incomplete data. Preterm labour was approved by their medical care records, ultrasound reports and notes on gestational age assessment of the newborn. The last menstrual period (LMP) was not eligible as this information was not documented in most of the medical records. The other was a control group (mothers with full-term delivery and their infants) consisting of 400 full-term deliveries (gestational age between 37 and 42 weeks) by vaginal delivery or CS, out of a total of 464 full-term deliveries, selected through a simple random sampling during the study period. Here, 20 medical records were excluded due to incomplete data (Figure 1).

Data collection

The study variables collected from the medical reports included background information of the mother (maternal age, education, current occupation, parity and gravidity), current pregnancy details (interval between the birth of the newborn baby and the previous delivery, total number of antenatal care (ANC) visits during the current pregnancy, presence of maternal medical illnesses [hypertension (HTN), diabetes, anaemia], history of vaginal infection, urinary tract infection (UTI), preeclampsia, premature rupture of membrane (PROM), abnormal amniotic fluid volume (polyhydramnios and oligohydramnios), antepartum haemorrhage (placenta previa and abruptio placenta) and mode of delivery). It also included past obstetric history (history of PTD and abortion), family history of PTD and newborn information (foetal position, multiple pregnancy, weight and sex).

Figure 1. The study design including the records of 591 live-born deliveries. FTNB, full-term newborn baby; PTNB, preterm newborn baby.

Definitions

• Prematurity: the WHO defines PTB as any birth before 37 completed weeks of gestation or fewer than 259 days since the 1^st day of woman’s LMP [1,2,6].
• Maternal age: the age of the mother at the time of delivery.
• Maternal educational level: it was categorised as primary (nine levels), secondary (three levels) and college. Those who cannot read or write were considered to be illiterate.
• ANC: the total number of ANC visits for the current pregnancy was categorised as ≥4 visits and <4 visits. The WHO and the United Nations International Children’s Emergency Fund recommended ≥4 ANC visits with an appropriate healthcare provider for pregnant women [2].
• Gravida: the number of all previous pregnancies including abortion and stillbirths.
• Parity: the number of previous pregnancies lasting more than 22 weeks’ gestation [3].
• The birth interval: The period between the previous delivery and the recent conception. The birth interval was calculated in years and was grouped into ≥2 years and <2 years.
• Anaemia in pregnancy is defined as a decrease in the concentration of circulating red blood cells or haemoglobin concentration (haemoglobin levels of below 11 g/dl) [21].
• HTN is defined as blood pressure ≥140 mmHg systolic or ≥90 mmHg diastolic (preferably confirmed by two readings, 4-6 hours separately) [18].
• Diabetes mellitus is defined as fasting blood sugar above 126 mg/dl in two separate measurements or random blood sugar more than 200 mg/dl with classic symptoms of hyperglycaemia [6].
• Mode of delivery was classified as vaginal delivery (including spontaneous vertex delivery, breech delivery and instrumental delivery) or lower segment CS.
• Vaginal infection and UTI were considered based on the clinical presentation as offensive vaginal discharge and itching in the case of vaginal infection and dysuria or intermittent micturition in the case of UTI.

Statistical analysis

The data were entered and analysed using the Statistical Package for the Social Sciences (version 24). We derived descriptive statistics (frequency and percentage) to determine the distribution of demographic information including maternal age, education and employment amongst case and control groups. The continuous data were compared between the two groups using Mann-Whitney U-test. The statistical relationship between the risk factors and PTB was assessed by applying the Chi-square (χ2) test (bivariate analysis), taking a level of significance of p < 0.05. The strength of association was assessed by calculating the odds ratio (OR) with a 95% confidence interval (CI). The variable was considered to have a statistically significant association with PTB if the χ2 p-value was <0.05, and the CI for the OR did not include the value 1.0. In case of inconsistency between χ2 and the OR, the result of the former was taken. The Fisher’s exact test was considered in the case of independent variables with a small size sample (number <5 in any cell). All variables displaying a significant relationship with PTD (p < 0.05) were entered into binary logistic regression (multivariate analysis). The results were reported as adjusted OR (AOR) and 95% CI along with the p-values. The independent variables with a small size sample were not enrolled in the model.

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RESULTS

In this study, maternal age for cases ranged between 16 and 45 years with a median (SD) of 25 (6.378) years, whereas, in the control group, the maternal age ranged between 14 and 45 years with a median (SD) of 26 (5.798) years. No statistically significant difference between the median age of the case and control groups (Z: −0.640, p-value: 0.522). Educated mothers form 77.4% of the study sample, 95.8% were housewives and only 4.2% were working mothers.

In the case group (mothers with PTD and their infants, Tables 1-3), PTD was common in the maternal age group of 14-25 years (51%) followed by >25-35 years (39%) and >35-45 years (10%). Illiterate mothers constituted 27%, 48% had primary education, 21% had secondary education and 4% had finished college. Only 3% were formally employed. The regular ANC (≥4 times) was recorded in 72% of cases, 38% were primigravida and 62% had a previous pregnancy. Premature delivery was common in mothers with gravida of ≤4 times (79%) and an interpregnancy spacing of ≥2 years (50.8%). Previous premature delivery, previous abortion and recurrent abortion (two or more) were noticed in 10%, 11% and 9% of cases, respectively. A positive family history of premature delivery was detected in 28% of cases.

Medical illnesses were recorded in 51% of cases. Chronic HTN was noticed in 18% of cases, and 26% of mothers in the premature group had preeclampsia during this pregnancy. Anaemia and diabetes mellitus were noticed in 32% and 3% of mothers, respectively.

UTI (59%) was more common than vaginal infection (45%). PROM was present in 34% of cases, and 24% had an abnormal amniotic fluid volume (7% with polyhydramnios and 17% with oligohydramnios). Placental abnormalities (4%) were also detected with placenta previa in 3% of cases.

Vaginal delivery (75%) was more common than CS (25%), and only 11.3% had a history of previous CS. A single foetus was the outcome in 93% of premature deliveries, 6% with twin delivery and 1% had triple babies. The male:female ratio of the premature newborns was 1:1.17 with 94% presenting with cephalic presentation.

In the control group (mothers with full-term delivery and their infants, Tables 1-3), full-term delivery was common in the maternal age group of 14-25 years (49%, n = 196), followed by >25-35 years (43%, n = 172) and >35-45 years (8%, n = 32). Illiterate mothers constituted 21.5% (n = 86), 49% (n = 196) had primary education, 23% (n = 92) had secondary education and 6.5% (n = 26) finished college. Only 4.5% (n = 18) were formally employed. A regular ANC (≥4 times) was recorded in 76.8% (n = 307) of mothers, 22.8% (n = 91) were primigravida and 77.3% (n = 309) had a previous pregnancy. A full-term delivery was common in mothers with a gravida of ≤4 times (78%, n = 312) and an interpregnancy spacing of <2 years (50.2%, n = 155). Mothers in the full-term control group had a history of previous premature delivery (3.3%, n = 13), previous abortion (6.5 %, n = 26) and recurrent abortion (two or more) (5.8%, n = 23). A positive family history of premature delivery was detected in 14.3% (n = 57) of mothers.

Table 1. Comparison between cases and controls by selected demographic and medical variables.

Variable	Cases		Controls		Total		χ2 value	OR	p-value
	No.	%	No.	%	No	%
Maternal age (years)							0.749	-	0.688
14-25	51	51	196	49	247	49.4
>25-35	39	39	172	43	211	42.2
>35-45	10	10	32	8	42	8.4
Mother working status							0.447	0.656	0.504bFisher’s test 0.366)
Employee	3	3	18	4.5	21	4.2
House wife	97	97	382	95.5	479	95.8
Education status							1.383	1.35	0.24
Not educated	27	27	86	21.5	113	22.6
Educated	73	73	314	78.5	387	77.4
Level of education							2.06	-	0.560
Illiterate	27	27	86	21.5	113	22.6
Primary	48	48	196	49	244	48.8
Secondary	21	21	92	23	113	22.6
College	4	4	26	6.5	30	6
Family history of PTB							10.72	2.34	0.001a
Yes	28	28	57	14.3	85	17
No	72	72	343	85.7	415	83
Medical illness							6.79	1.79	0.009a
Yes	51	51	147	36.8	198	39.6
No	49	49	253	63.3	302	60.4
Chronic HTN							26.35	5.634	0.000a
Yes	18	18	15	3.8	33	6.6
No	82	82	385	96.3	467	93.4
Eclampsia							40.45	6.34	0.000a
Yes	26	26	21	5.3	47	9.4
No	74	74	379	94.8	453	90.6
Diabetes							2.318	3.06	0.128b (Fisher’s test 0.147)
Yes	3	3	4	1	7	1.4
No	97	97	396	99	493	98.6
Anaemia							0.084	1.072	0.771
Yes	32	32	122	30.5	154	30.8
No	68	68	278	69.5	346	69.2

HTN, hypertension; OD, odds ratio; PTB, preterm birth; χ2, Chi-square.

^aVariables with statistical significance in relation to PTB.

^bVariables with cell count less than 5.

Medical illnesses were recorded in 36.8% (n = 147) of cases in the control group. Chronic HTN was recorded in 3.8% (n = 15) of mothers, and 5.3% (n = 21) of mothers in the full-term control group had pre-eclampsia during this pregnancy. Anaemia and diabetes mellitus were recorded in 30.5% (n = 122) and 1% (n = 4) of mothers, respectively.

Table 2. Comparison between cases and controls by selected maternal past obstetric history.

Variable	Cases		Controls		Total		χ2 value	OR	p-value
	No.	%	No.	%	No.	%
Parity							9.719	2.081	0.002a
Nulliparous	38	38	91	22.8	129	25.8
Multiparous	62	62	309	77.3	371	74.2
Gravidity							0.047	0.942	0.828
>4 times	21	21	88	22	109	21.8
≤4 times	79	79	312	78	391	78.2
Interval between the past two pregnancies (yrs)c							0.019	0.963	0.890
<2	31	49.2	155	50.2	186	50
≥2	32	50.8	154	49.8	186	50
History of previous PTB							8.306	3.308	0.004b (Fisher’s test 0.008)
Yes	10	10	13	3.3	23	477
No	90	90	387	96.8	4.6	95.4
History of previous abortion							2.364	1.778	0.124
Yes	11	11	26	6.5	37	7.4
No	89	89	374	93.5	463	92.6
History of recurrent abortion							1.41	1.62	0.235
Yes	9	9	23	5.8	32	6.4
No	91	91	377	94.3	468	93.6
History of previous CSc							0.214	1.229	0.644
Yes	7	11.3	29	9.4	36	9.7
No	55	88.7	280	90.6	335	90.3

CS, caesarean section; OD, odds ratio; χ2, Chi-square; yrs, years.

^aVariables with statistical significance in relation to PTB.

^bVariables with cell count less than 5.

^cMissing cases were not included in the total sample count.

UTI (51.5%, n = 206) was common than vaginal infection (31.8%, n = 127). PROM was present in 12.8% (n = 51) of mothers, and 9.5% (n = 38) had an abnormal amniotic fluid volume (polyhydramnios in 1.8% and oligohydramnios in 7.8%). Placental abnormalities (2.8%, n = 11) were also detected with placenta previa in five mothers (1.3%).

Vaginal delivery (78%, n = 312) was more common than CS (22%, n = 88), and only 9.7% (n = 36) had a history of previous CS. The single foetus was the outcome in 98.3% (n = 393) of full-term deliveries, and 1.8% (n = 7) of mothers had twin delivery. The male:female ratio of the full-term newborns was 1:1, and 94.5% (n = 378) presented with cephalic presentation.

Statistical significance

In bivariate analysis (Tables 1-3), the risk factors for premature delivery considered statistically significant were primigravida mothers (p = 0.002, OR 2), family history of premature delivery (p = 0.001, OR 2.34), previous premature delivery (the Fisher’s exact test 0.008, OR 3.31), presence of medical illness (p = 0.009, OR 1.79), chronic HTN (p = 0.000, OR 5.63), pre-eclampsia (p = 0.000, OR 6.34), vaginal infection (p = 0.013, OR 1.76), PROM (p = 0.000, OR 3.53), abnormal amniotic fluid volume (p = 0.000, OR 3) [polyhydramnios (the Fisher’s exact test 0.011, OR 4.23) and oligohydramnios (p = 0.005, OR 2.44)], and multiple pregnancy (more than one foetus) (the Fisher’s exact test 0.011, OR 0.237).

Table 3. Comparison between cases and controls by selected maternal recent pregnancy.

Variable	Cases		Controls		Total		χ2 value	OR	p-value
	No.	%	No.	%	No.	%
ANC							0.984	1.284	0.321
<4 times	28	28	93	23.3	121	24.2
≥4 times	72	72	307	76.8	379	75.8
Vaginal infection							6.224	1.76	0.013a
Yes	45	45	127	31.8	172	34.4
No	55	55	273	68.3	328	65.6
UTI							1.81	1.36	0.179
Yes	59	59	206	51.5	265	53
No	41	41	194	48.5	235	47
PROM							25.6	3.53	0.000a
Yes	34	34	51	12.8	85	17
No	66	66	349	87.3	415	83
Abnormal amniotic fluid volume							15.49	3.01	0.000a
Yes	24	24	38	9.5	62	12.4
No	76	76	362	90.5	438	87.6
Polyhydramnios							8.102	4.226	0.004b (Fisher’s test 0.011)
Yes	7	7	7	1.8	14	2.8
No	93	93	393	98.3	486	97.2
Oligohydramnios							7.887	2.438	0.005a
Yes	17	17	31	7.8	48	9.6
No	83	83	369	92.3	452	90.4
Placental abnormalities							0.43	1.47	0.512b (Fisher’s test 0.351)
Yes	4	4	11	2.8	15	3
No	96	96	389	97.3	485	97
Placenta previa							1.56	2.44	0.212b (Fisher’s test 0.202)
Yes	3	3	5	1.3	8	1.6
No	97	97	395	98.8	492	98.4
Mode of delivery							0.412	0.846	0.521
Vaginal delivery	75	75	312	78	387	77.4
CS	25	25	88	22	113	22.6
Foetal malposition							0.038	1.097	0.846
Yes	6	6	22	5.5	28	5.6
No	94	94	378	94.5	472	94.4
Type of pregnancy							8.102	4.226	0.004b (Fisher’s test 0.011)
Multiple	7	7	7	1.8	14	2.8
Singleton	93	93	393	98.3	486	97.2
Foetal sex							0.392	1.15	0.531
Male	54	54	202	50.5	256	51.2
Female	46	46	198	49.5	244	48.8

ANC, antenatal care; CS, caesarean section; OD, odds ratio; PROM, premature rupture of membranes; UTI, urinary tract infection.

^aVariables with statistical significance in relation to PTB.

^bVariables with cell count less than 5.

Other independent variables with no statistically significant association as a risk factor of premature delivery include maternal age, educational level of the mother, occupation, ANC ≤4 times, gravida more than four, interpregnancy spacing <2 years, history of previous abortion, recurrent abortion, anaemia, diabetes mellitus and UTI, presence of placental abnormalities, CS as a mode of the recent or previous delivery, foetal sex and foetal malposition.

Table 4 shows the results of logistic regression (multivariate analysis). A family history of PTD (AOR 2.353; CI 1.3-4.258, p-value 0.005), pre-eclampsia (AOR 4.120; CI 1.918-9.340, p-value 0.001), parity (AOR 2.139; CI 1.249-3.662, p-value 0.006), PROM (AOR 4.161; CI 2.323-7.456, p-value 0.000) and abnormal amniotic fluid volume (AOR 4.534; CI 1.364-15.071, p-value 0.014) were all significantly associated with PTD.

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DISCUSSION

The data included in the present study revealed that a family history of PTD, preeclampsia, parity, PROM and abnormal amniotic fluid volume were statistically significant risk factors for PTD. To the best of author’s knowledge, this is the first study conducted in Yemen studying a large number of independent variables as risk factors concerning PTB.

The risk factors of PTB are multifactorial. Some of which are preventable and curable, whereas, in most of the cases, the exact causes of preterm labour are unknown [18]. Genetic susceptibility may play a key role in the aetiology of PTB [22]. The epidemiological studies demonstrate that mothers, sisters and daughters share the risk for PTB [22]. A family history of PTB is an independent risk factor for PTB in subsequent generations [23,24]. It is not only limited to the mother herself but also can include her other relatives (siblings and sisters) [19,23,24]. In this study, a family history of PTD was considered as a statistically significant risk factor for PTD (OR 2.353, CI 1.3-4.258, p = 0.005). A similar finding was reported by Boivin et al. [25] and Sherf et al. [23].

Table 4. Logistic regression of risk factors affecting PTD.

Variables	B	Standard error	Wald	df	p-value	AOR	95% CI for OR
							Lower	Upper
Family history of PTD	0.856	0.303	7.995	1	0.005a	2.353	1.300	4.258
Medical illnesses	0.289	0.274	1.117	1	0.291	1.336	0.781	2.285
HTN	0.705	0.527	1.794	1	0.180	2.025	0.721	5.684
Pre-eclampsia	1.416	0.418	11.498	1	0.001a	4.120	1.818	9.340
Parity	0.760	0.274	7.682	1	0.006a	2.139	1.249	3.662
Vaginal infection	0.406	0.258	2.481	1	0.115	1.501	0.906	2.489
PROMs	1.426	0.298	22.966	1	0.000*	4.161	2.323	7.456
Abnormal amniotic fluid volume	1.512	0.613	6.083	1	0.014a	4.534	1.364	15.071
Oligohydramnios	1.359	0.707	3.692	1	0.055	0.257	0.064	1.028

df, degrees of freedom; Confidence interval; OD, odds ratio.

^aStatistically significant.

In this study, medical illness and HTN (essential and pregnancy-induced) showed an association with PTB in bivariate analysis. Preeclampsia-eclampsia was a significant risk factor for PTB in bivariate analysis (OR 6.34, p = 0.000) and multivariate analysis (AOR 4.120, CI 1.818-9.340, p = 0.001). According to the study of Goldenberg et al. [8], maternal complications related to HTN might be associated with an increased risk of PTD. Bakhteyar et al. [26] and Davies et al. [27] reported a more than four-fold increase in the risk of PTB in mothers with pre-eclampsia. The other studies support the association between pre-eclampsia and PTB [28–32].

A parity as a significant risk factor of PTD was shown in this study (AOR 2.139, CI 1.249-3.662, p = 0.006). This finding was supported by the other studies that reported an association between primiparity and PTB [33–35]. Ananth et al. [36] considered primiparity as an intermediate risk factor for spontaneous and medically indicated PTB. Mayo et al. [37] reported an increased risk of spontaneous PTB in nulliparous teenagers, especially those 16 years or younger. In comparison between nulliparous and parous women, Koullali et al. [38] found that high parity, as well as nulliparity, is considered as a risk factor for spontaneous PTB, whereas Waldenström et al. [39] and Chan and Lao [40] suggested that advanced maternal age influences the risk of PTB regardless of parity.

PROMs proceed about 20%-30% of PTBs [5,8]. Mothers with PROM had 5.11 times higher risk for PTB (CI 2.69-9.69, p ≤ 0.001) [26]. This study found that PROM is a statistically significant risk factor for PTD (AOR 4.161, CI 2.323-7.456, p = 0.000). The same finding was supported by the other studies [32,41]. The reverse was shown by Carter et al. [31], who reported no significant association between PROM and PTB (AOR 1, CI 0.91-1.11).

In this study, abnormality in amniotic fluid volume was reported in mothers with PTD (24%) and showed a statistically significant association as a risk factor for PTB in both bivariate analysis (p = 0.000) and multivariate analysis (AOR 4.534, CI 1.364-15.071, p = 0.014). Studying the effect of oligohydramnios and polyhydramnios separately on PTB revealed a statistical significance in bivariate analysis ([oligohydramnios (p = 0.005) and polyhydramnios (Fisher’s exact test 0.011)] but not in multivariate analysis. This might be related to the small sample size in this study. Goldenberg et al. [8] reported an association between extremes in the volume of amniotic fluid (oligohydramnios or polyhydramnios) with PTB and PROM. Several studies supported an increased risk of preterm labour with oligohydramnios [28,32,42]. Lo et al. [43] reported an ten-fold increase in the risk for early preterm labour in women with oligohydramnios. On the contrary, Ahumada-Barrios and Alvarado [30] reported no significant association between oligohydramnios and PTB. In a study carried by Many et al. [44], preterm labour was related to the underlying cause of polyhydramnios rather than the excess fluid amount. Mahapula et al. [45] reported an increased risk of PTD in women with polyhydramnios (AOR 8.3, CI 1.7-40.2, p-value 0.008).

Strength and limitations

The strength of this study relies on being conducted in Mukalla MHC Hospital which is the oldest hospital in the area and considered as a referral hospital for high-risk pregnancies and women with complications. Another supporting point is the lack of similar previous studies conducted in this area. Hence, the results extend knowledge on the common risk factors influencing PTD in Mukalla. Several limitations should be considered when the results of this study are interpreted. The first main limitation of the present study was the use of retrospective cross-sectional data to determine the influence of risk factors in PTD. Hence, further longitudinal analyses with larger samples will provide stronger evidence in this topic and allow a better generalisation of the results to other populations. Second, the rate of PTB was underestimated as the study was conducted in one hospital, and stillbirths were excluded from the study. Deliveries in private hospitals and home deliveries were not included. Third, the risk factors such as maternal malnutrition, presence of congenital infection, uterine anomalies, use of herbal therapy, history of abdominal trauma and medical illnesses as bronchial asthma, heart disease and renal disease were not assessed either due to the lack of information in the records or due to low prevalence amongst the studied population. Finally, gestational age assessment was based on data from medical records, ultrasound reports and notes on gestational age assessment of the newborn. This is because the date of the first day of the LMP was not included in most of the medical records.

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CONCLUSIONS

In this study, a family history of PTD, pre-eclampsia, parity, PROM and abnormal amniotic fluid volume are the risk factors for premature delivery. Recognising the most common risk factors for PTD will help to increase the awareness about high-risk pregnancy, improve the preventive measures of preterm risk factors and modify preterm care protocol in nurseries.

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CONFLICT OF INTEREST

The authors declare that there is no conflict of interest regarding the publication of this article.

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FUNDING

None.

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ETHICAL APPROVAL

The study was approved, and an ethical clearance was given by the Ethics Committee of Hadhramout University College of Medicine (HUCOM), Yemen. The study is a retrospective (record-based) case-control study. No names were used for data collection. Participants’ consent is not required according to the approved research guidelines of HUCOM, and confidentiality was ensured at all levels.

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