INTRODUCTION
Postdate pregnancies are associated with significantly increased foetal and neonatal risk such as still birth and perinatal mortality, largely due to placental insufficiency and reduced uteroplacental perfusion (WHO Recommendations on Induction of Labour, at or beyond Term, n.d.). These pregnancies are also associated with other maternal and foetal complications during pregnancy ,delivery, and postpartum period including meconium stained liquor , prolonged labour , increased caesarean section, perineal tear and post partum haemorrhage (Awadalla Abdelwahid et al., 2023; Betcher & Berken, 2019). Postdate pregnancy ,defined as gestation beyond 40 weeks (280 days) from last normal menstrual period (LNMP), affects up to 10% of pregnancies where as postterm pregnancy refers to a pregnancy that has continue beyond 42 weeks (Awadalla Abdelwahid et al., 2023).
Globally, the prevalence of postdate pregnancy varies significantly, ranging from 3% to 14% (Awadalla Abdelwahid et al., 2023). This variation is attributed to differences in gestational age estimation methods and management protocols (Crowley, 2006; Zeitlin et al., 2007).In developed countries such as Finland, the prevalence is approximately7% (Deng et al., 2019; Hovi et al., 2006). In Africa, the burden varies by region, with estimates of 9% in Nigeria and approximately 5% in East Africa (Auma, 2023; Awoyesuku et al., 2023). Despite regional differences, complications associated with postdate pregnancy remain consistent across settings.
The exact cause of postdate pregnancy remains unknown due to complex mechanisms involved in labour initiation. Contributing factors include inaccurate dating from incorrect LNMP records (Jehan et al., 2010), genetic factors (Laursen et al., 2004), primigravida status, young maternal age (Deng et al., 2019), foetal factors such as male gender (Divon et al., 1996), and placental sulphatase deficiency (Caughey et al., 2007).
As pregnancy advances beyond the expected due date, risks of maternal and perinatal complications increase (Caughey et al., 2007). Prolonged pregnancy is associated with placental insufficiency, oligohydramnios, meconium passage, abnormal intrapartum foetal heart rates, macrosomia, prolonged labour, postpartum haemorrhage, perineal trauma, and increased rates of induction and caesarean section (Caughey et al., 2007; Chanu et al., 2023; Karmakar et al., 2020). Perinatal morbidity and mortality also increase with advancing gestation (Bs et al., 2017).
In Sub-Saharan Africa , early antenatal care (ANC) attendance in the first trimester is only 38% (Abdo et al., 2023), meaning over 60% of women initiate ANC in later trimesters, increasing their risk of postdate pregnancy due to lack of early ultrasound dating.
In Kenya , induction of labour is offered at 41 weeks in accordance with national guidelines (Ministry of Health Kenya, 2022). However, no local studies have been conducted to determine whether complications occur even before 41 weeks. This study aimed to evaluate outcomes of postdate pregnancy among women delivering at CGTRH, Mombasa, Kenya.
METHODS
Study Design and Setting
This unmatched prospective case-control study was conducted from January to June 2025 at the maternity unit of a tertiary referral hospital in coastal Kenya. The study site is a county teaching and referral hospital handling approximately 7,000 deliveries annually, with a 154-bed maternity unit and the only neonatal intensive care unit in the coastal region.
Study Population and Sampling
Cases were women with postdate pregnancies (>40 weeks gestation). Controls were women with term pregnancies (37–39 completed weeks) in a 1:4 ratio. Using the OpenEpi sample size calculator with assumptions of 95% confidence interval, 80% power, case-to-control ratio 1:4, and odds ratio of 1.8 based on a previous study (Hochler et al., 2023), the calculated sample size was 114 cases and 456 controls (total n=570). Purposive sampling was employed for cases due to rarity of the condition, and systematic random sampling for controls (every third eligible delivery).
Inclusion and Exclusion Criteria
Women with singleton pregnancies from 37 completed weeks and beyond, with gestational age determined by LNMP or first-trimester ultrasound, who consented to participate were included. Women with unknown LNMP or no first-trimester ultrasound, contraindications to vaginal delivery, adverse medical conditions (HIV, diabetes, hypertensive disorders, anaemia, thyroid or cardiac disease), or multiple gestations were excluded.
Data Collection
A pre-piloted structured questionnaire was administered to consenting participants by the principal investigator and three trained research assistants. Delivery registers were used to identify eligible participants. The principal investigator and three trained research assistants obtained consent and interviewed eligible participants at post natal ward. Data collected included sociodemographic characteristics, obstetric history, antenatal care details, maternal outcomes (mode of delivery, labour characteristics, postpartum haemorrhage, perineal tears), and foetal outcomes (birth weight, Apgar scores, meconium aspiration, NICU admissions, stillbirths).
Statistical Analysis
Data were entered into Microsoft Excel and analysed using SPSS version 28. Descriptive statistics summarised categorical variables as frequencies and proportions, and continuous variables as means with standard deviations. Comparisons between groups were performed using Chi-square tests and logistic regression at 95% confidence interval. A p-value <0.05 was considered statistically significant.
Reporting Guidelines
This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines for case-control studies.
Ethical Considerations
Ethical approval was obtained from the institutional ethics review committee (ERC-CGH/MSc/VOL.1). Written informed consent was obtained from all participants. Confidentiality was maintained by anonymizing data and restricting access to study records.
RESULTS
Participant Characteristics
A total of 570 women participated: 114 with postdate pregnancies and 456 with term pregnancies. The overall mean age was 26.5 years (SD 5.4; range 18–43). Age distribution did not differ significantly between groups (p=0.475). Sociodemographic characteristics were comparable, with no significant differences in marital status (p=0.908), education level (p=0.162), employment status (p=0.849), or religion (p=0.455). (Table 1)
Clinical Characteristics
Mean gravidity was 1.9±1.3 in the postdate group and 2.2±1.4 in the term group (p=0.114). Gestational age by LMP averaged 40.9±0.8 weeks in postdate versus 38.3±0.8 weeks in term (p<0.001). Early ultrasound confirmation was available for only 2.3% of participants. Antenatal care visits were significantly higher in the postdate group (5.2 vs 4.6; p<0.001), and early booking (<12 weeks) was more common among postdate participants (25.4% vs 12.7%; p=0.003). A prior history of postdate pregnancy was reported in 9.6% of cases versus 0.2% of controls (p<0.001). (Table 2)
Maternal Outcomes
Spontaneous labour occurred less frequently in postdate pregnancies (89.5% vs 99.3%; p<0.001). Labour augmentation was required more often (42.1% vs 18.4%; p<0.001). Meconium-stained liquor was observed in 48.2% of postdate cases versus 3.7% of term pregnancies (p<0.001).
Caesarean section was performed in 42.1% of postdate women compared to 7.9% of term women (p<0.001). Indications for caesarean section included non-reassuring foetal heart rate (20.7%), slow progress (21.9%), macrosomia (7.3%), and cephalopelvic disproportion (1.2%).
Perineal outcomes showed significant differences (p<0.001): second-degree tears occurred in 14.9% of postdate deliveries versus 5.0% of term deliveries. Postpartum haemorrhage (estimated blood loss >500 mL) occurred in 25.4% of postdate women compared to 2.4% of term women (p<0.001). (Table 3)
Foetal Outcomes
Irregular intrapartum foetal heart rate was recorded in 19.3% of postdate pregnancies versus 3.7% of term pregnancies (p<0.001). Fresh stillbirths occurred exclusively in the postdate group (2.6%).
Macrosomia (birthweight >4000 g) was observed in 24.6% of postdate infants versus 4.2% of term infants (p<0.001). Apgar scores at 5 minutes were significantly lower in postdate neonates (p=0.0115). Meconium aspiration syndrome affected 7.9% of postdate neonates versus 1.1% of term neonates (p<0.001). Newborn unit admissions were significantly higher for postdate neonates (12.3% vs 1.5%; p<0.001). Early perinatal mortality did not differ significantly between groups (0.9% vs 0.2%; p=0.859). (Table 4)
Predictors of Postdate Pregnancy
Logistic regression identified previous postdate pregnancy as the strongest independent predictor of recurrence (AOR = 78.65; 95% CI: 9.15–676.36; p<0.001). Higher gravidity was protective (AOR = 0.59; 95% CI: 0.37–0.95; p=0.029). Lack of formal education was associated with increased risk (AOR = 4.21; 95% CI: 1.26–14.08; p=0.020). Early ANC booking and number of ANC visits were not significant in the multivariable model. (Table 5)
DISCUSSION
This study evaluated obstetric outcomes associated with postdate pregnancy at a tertiary referral hospital in coastal Kenya. The findings demonstrate that postdate pregnancy is associated with significantly worse maternal and perinatal outcomes compared to term pregnancy.
Sociodemographic Characteristics
Socio-demographic factors were largely homogeneous between groups, indicating well-matched populations. No significant association was found between maternal age and postdate pregnancy (p=0.475), aligning with multicentre studies suggesting minimal effect of general demographic distribution on gestational length (Hochler et al., 2023; Zhou & Yin, 2023).
However, multivariable regression revealed that women with no formal education had significantly greater likelihood of postdating (AOR = 4.21; p=0.020), consistent with regional African settings where lower literacy correlates with delayed care-seeking (Adedokun & Yaya, 2020).
Maternal Outcomes
Spontaneous labour occurred less frequently in postdate pregnancies (89.5% vs 99.3%; p<0.001), and labour augmentation was required more often (42.1% vs 18.4%). This aligns with literature suggesting postdate pregnancy is typified by decreased uterine sensitivity and delayed cervical ripening (Galal et al., 2012).
Meconium-stained liquor was significantly more common in postdate deliveries (48.2% vs 3.7%; p<0.001), reflecting placental aging and foetal hypoxia triggering colonic activity (Gallo et al., 2024).
Caesarean section rates were markedly higher in postdate pregnancies (42.1% vs 7.9%; p<0.001), consistent with evidence that operative risk increases linearly with gestational age due to foetal size and inefficient uterine action (Källén et al., 2025).
Postpartum haemorrhage was significantly more common (25.4% vs 2.4%; p<0.001), concurring with clinical reviews indicating reduced uterine contractility from prolonged labour and macrosomic overdistension (Turkmen & Binfare, 2024).
Foetal Outcomes
Intrapartum foetal distress was significantly more prevalent in postdate pregnancies (19.3% vs 3.7%; p<0.001), consistent with regional data attributing this to reduced placental respiratory function (Afridi et al., 2024).
Macrosomia was markedly higher (24.6% vs 4.2%; p<0.001), reflecting continued foetal growth beyond term. Meconium aspiration syndrome affected 7.9% of postdate neonates versus 1.1% at term (p<0.001), confirming that hypoxic stress triggers the foetal gasping reflex.
Newborn unit admissions were significantly higher (12.3% vs 1.5%; p<0.001), with respiratory distress as the primary indication. Fresh stillbirths occurred exclusively in the postdate group (2.6%), consistent with population-level data demonstrating critical windows where placental performance declines below foetal metabolic needs (Källén et al., 2025).
Predictors of Postdate Pregnancy
A prior history of postdate pregnancy was the strongest independent predictor of recurrence (AOR = 78.65; p<0.001), mirroring findings from other settings where recurrence risk is a primary driver (Mitao et al., 2023). Gravidity was protective, with each additional pregnancy decreasing odds by 41% (AOR = 0.59; p=0.029). Early ANC booking and number of ANC visits lost significance after adjustment, indicating confounding by other variables.
Strengths and Limitations
Strengths include the large sample size, case-control design suitable for examining outcomes in specific groups, and conduct at a high-volume referral hospital ensuring representative population.
Limitations include potential referral bias (women with anticipated complications more likely to deliver at facility), reliance on LMP for dating (only 2.3% had early ultrasound), and retrospective retrieval of some history data subject to record-keeping accuracy.
CONCLUSION
This study concludes that postdate pregnancy at this tertiary referral hospital is associated with significantly worse maternal and perinatal outcomes compared to term pregnancy. Prolonged gestation alters labour physiology, resulting in reduced spontaneous labour, increased obstetric interventions, and higher maternal morbidity—particularly postpartum haemorrhage and severe perineal trauma. Foetal risks include macrosomia, meconium aspiration, newborn unit admission, and stillbirth, likely related to declining placental function beyond 40 weeks. A previous postdate pregnancy is the strongest predictor of recurrence, while higher gravidity is protective.
These findings support classifying postdate pregnancy as a high-risk condition requiring active surveillance, timely induction, and close intrapartum monitoring to reduce preventable complications.
Ethics Approval and Consent to Participate
Ethical approval was obtained from the institutional ethics review committee (ERC-CGH/MSc/VOL.1). Written informed consent was obtained from all participants.
Consent for Publication
Not applicable.
Availability of Data and Materials
The datasets generated and analysed during this study are available from the corresponding author upon reasonable request.
Competing Interests
The authors declare no competing interests.
Funding
This research received no specific grant from any funding agency.
Authors’ Contributions
SRK: conceptualization, data collection, analysis, drafting; RS: supervision, methodology, review; MM: supervision, conceptualization, revision. All authors read and approved the final manuscript.
Acknowledgments
The authors thank the staff at the maternity unit and all study participants for their contributions.