Caesarean section is associated with an increased risk of placental disorders in future pregnancies, but the effects on stillbirth rates are unknown. Gordon Smith from the University of Cambridge, UK, and colleagues assessed whether previous caesarean delivery is associated with an increased risk of stillbirth.
Using data for 120,000 births in Scotland between 1992 and 1998, the proportion of stillbirths was greater (2.4 per week per 10,000 women) for women who had previously given birth by caesarean section than women who had undergone previous vaginal delivery (1.4 per 10,000 women per week). The increased risk of stillbirth-mainly stillbirth without any known cause-started at around 34 weeks of the second pregnancy for those women who had previously undergone caeserean section for their first child. The risk of stillbirth was the same regardless of the reason for the original caesarean section.
Gordon Smith comments: "Our results are of relevance for women considering caesarean delivery who are planning further pregnancies. The absolute risk of perinatal death associated with vaginal breech delivery at term is around 8.3 per 1000 births. Caesarean section reduces the risk of perinatal morbidity and mortality associated with vaginal breech birth. The overall excess risk of stillbirth in a second pregnancy that was associated with a previous caesarean delivery was below one per 1000, which is unlikely to influence the decision to have a caesarean section for breech presentation in a first pregnancy. However, if women are being counselled about caesarean birth with no clear obstetric advantage, such as caesarean section for maternal request, the possible effect on the risk of unexplained stillbirth in future pregnancies should be discussed."
In an accompanying Commentary (p 1774), Judith Lumley from the Centre for the Study of Mothers' and Children's Health, Australia, states: "The finding...that caesarean section increases the risk of unexplained stillbirth before labour in the next pregnancy has the potential to redefine the nature of the debate about the place of caesarean delivery in maternity care. She concludes: "Smith and colleagues' paper also reminds us that when we wonder why preterm birth and unexplained antepartum stillbirths remain such a constant feature of perinatal outcomes in developed countries, the actual causative factors may be varying through unrecognised changes in perinatal care."