Risk of Subsequent Preterm Delivery Following C-section Births

Abstract

Background: Complications due to preterm birth (prior to 37 weeks of gestation) are the leading causes of deaths among children under 5 years of age. Factors known to increase risk include socio-demographics, maternal health status before and during pregnancy, obstetrics-related conditions, and environmental factors such as climate change and air pollution. The association between prior C-section and preterm delivery in subsequent births remains inconclusive in the published literature. Aim: This study aims to: 1) examine the association between C-section deliveries and subsequent preterm births, controlling for major predictors of preterm birth. 2) examine the association between increasing numbers of prior C-sections and odds of preterm birth. Methods: A case control study was conducted. The population includes women who gave birth between 2009 and 2019 in hospitals enrolled with National Collaborative Perinatal Neonatal Network. Cases included 12,049 pregnant mothers who gave birth prior to 37 gestational weeks with para>0. Controls included 48,196 mothers who had delivered post 37 gestational weeks with para>0. Cases and controls (1:4 ratio) were frequency-matched on newborn year of birth and gender and maternal place of residence. Case status was handled as a categorical variable representing stages of preterm birth (“extremely preterm birth”, “very preterm birth”, and “moderate to late preterm birth”). The two main exposures included presence of a previous C-section and number of previous C-section births. Crude and adjusted odds ratios and their 95% confidence interval were estimated by multinomial logistic regression models adjusting for measured confounders. Results: The odds of having undergone a previous C-section was 1.3 times more likely in cases with moderate-to-late preterm birth (32-<37 weeks) [adjusted OR=1.3, 95% CI (1.21 – 1.38)] than in controls (full-term birth) controlling for measured covariates. There was also a statistically significant increase in the odds of moderate to late preterm birth vs. full-term birth with increasing number of previous C-sections, controlling for measured covariates. This increase reached almost a 3-fold rise in odds when the number of previous C-sections was five or more in comparison to no previous C-section [adjusted OR=2.85, 95% CI (1.50 – 5.42)]. The odds of having undergone 5 previous C-sections was 5.25 times more likely in cases with extreme preterm birth (<28 weeks) [adjusted OR= 5.25, 95% CI (1.03-26.65)] than in controls (full-term birth), controlling for measured confounders. Conclusion: C-section delivery in the first pregnancy is shown to be a significant risk factor for moderate to late preterm birth in subsequent delivery even after adjusting for other predictors of preterm birth. Findings emphasize the importance of restricting elective C-section deliveries, particularly among mothers who are at risk of premature delivery.