Objective: Two recent studies indicate an increased risk of stillbirth in the pregnancy that follows a pregnancy delivered by caesarean section. In this study, we report an analysis designed to test the hypothesis that delivery by caesarean section is a risk factor for explained or unexplained stillbirth in any subsequent pregnancy. We also report on the proportion of stillbirths in our study population, which may have been attributable to previous delivery by caesarean section.
Design: Retrospective cohort study.
Population: Linked statistical data set of 81 784 singleton deliveries registered in Oxfordshire and West Berkshire between 1968 and 1989.
Methods: The crude and adjusted hazard ratios for stillbirth in deliveries following a previous delivery by caesarean section, compared with no previous caesarean, were estimated using Cox regression.
Main outcome measure: Stillbirth.
Results: The unadjusted hazard ratios for all, explained, and unexplained stillbirths were 1.54 (95% CI 1.04-2.29); 2.13 (1.22-3.72); and 1.19 (0.68-2.09), respectively. After adjustment for maternal age, parity, social class, previous adverse outcome of pregnancy, body mass indexand smoking the hazard ratios were 1.58 (0.95-2.63), 2.08 (1.00-4.31) and 1.24 (0.60-2.56).
Conclusions: Pregnancies in women following a pregnancy delivered by caesarean section are at an increased risk of stillbirth. In our study, the risk appears to be mainly concentrated in the subgroup of explained stillbirths. However, there are sufficient inconsistencies in the developing literature about stillbirth risk that further research is needed.