When pregnancies last for 40 weeks or longer, there is a significant additional risk of stillbirth and neonatal death, according to the results of a large review of studies.
The meta-analysis also found that prolonging pregnancy beyond 40 weeks did not reduce the risk for death in the baby’s first month of life (neonatal mortality).
Prolongation of pregnancy at term is a known risk factor for stillbirth. Currently women are routinely offered induction of labour after 41 weeks gestation to avoid stillbirth. But 1 in 3 stillbirths will happen prior to this gestational age.
The review, published in PLOS Medicine, combined data from 13 studies of stillbirth and neonatal death involving more than 15 million pregnancies.
The researchers found that stillbirths steadily rose with gestational age, from 0.11 per thousand births at 37 weeks to 3.18 per thousand at 42 weeks.
In mothers who continued their pregnancy to 41 weeks, there was a 64% increase in the risk of stillbirth compared to those who delivered at 40 weeks, with 1 additional mother having a stillborn baby for every 1,449 women.
“Women need to be aware that there is a small but increasing risk after 40 weeks of gestation,” said the senior author, Shakila Thangaratinam, a professor at Queen Mary University of London. “But induction is a medical procedure that some mothers won’t want. We have to give mothers the information that empowers them to make a decision. We want to promote joint decision making between mother and doctor.”