Caesarean section delivery of a first pregnancy doubles the risk of unexplained antepartum stillbirth at or after 39 weeks' gestation in a second pregnancy, according to a study from the United Kingdom involving data on over 100,000 births.
Researchers analyzed pregnancy discharge data from the Scottish Morbidity Record between 1980 and 1998 and from the Scottish Stillbirth and Infant Death Enquiry for 1985 to 1998. They found that women who delivered their first pregnancy by C/S had a rate of antepartum stillbirth that was 2.39 per 10,000 women per week, while those who delivered their first pregnancy vaginally had a rate of 1.44. The absolute risk of unexplained stillbirth at or after 39 weeks' gestation was 1.1 per 1,000 women who had a previous C/S versus 0.5 per 1,000 for those who did not.
The researchers say the link between C/S and stillbirth is biologically plausible because intentional or inadvertent ligation of major uterine vessels during the first C/S can alter uterine blood flow in future pregnancies. Another possible explanation is that stillbirth results from abnormal placentation caused by uterine scarring.
A commentary in the same issue of the Lancet raises the question of whether, as a result of the findings, all women with a previous C/S should be booked for repeat C/S deliveries at 38 weeks or earlier. At the very least, the authors of the study say that all pregnant women considering C/S delivery for any reasons other than absolute medical necessity should be counseled about the risks of the procedure to current and future pregnancies.
Smith GC, Pell JP, Dobbie R. Caesarean section and risk of unexplained stillbirth in subsequent pregnancy. Lancet. 2003;362:1779-1784.
Lumley JM. Unexplained antepartum stillbirth in pregnancies after a cesarean delivery. Lancet. 2003;362:1774-1775.