Associations between previous cesarean section and maternal and neonatal complications: the modification of long inter-pregnancy interval

Objectives We aim to explore whether the long inter-pregnancy interval (IPI) modifies the association between previous cesarean section (CS) and adverse maternal and neonatal outcomes in a population with a high rate of CS and a long IPI. Methods Adverse maternal and neonatal outcomes were compared between the previous CS and previous vaginal delivery groups. Logistic models were used to adjust for potential confounding factors and calculate the Odds Ratios (ORs) and 95 % confidence intervals (CIs). The interaction model and stratified analyses were used to evaluate the modifications of IPIs on the associations between previous CS and maternal and neonatal outcomes. Results Compared with previous vaginal delivery, previous CS was associated with increased risks of uterine-related complications (a OR=1.57, 95 % CI 1.25–1.98), but with decreased risks of preterm birth (a OR=0.73, 95 % CI 0.63–0.85) and severe neonatal adverse outcomes (a OR=0.59, 95 % CI 0.46–0.78). There are synergistic biological interaction effects of previous CS and a long IPI (>60 months) on the risks of placental-related complications (RERI=0.32, 95 % CI 0.05–0.58; AP=0.39, 95 % CI 0.03–0.76) but an antagonistic biological interaction effect on the risk of preterm birth (RERI=−0.35, 95 % CI -0.68 to −0.01; AP=−0.09, 95 % CI -0.68 to −0.03). Conclusions Previous CS was associated with increased risks of adverse maternal outcomes but decreased risks of certain adverse neonatal outcomes. Prolonged IPIs might not attenuate the adverse effects of previous CS on mothers, and might adversely exert harm on newborns.