When pregnancies last for 40 weeks or longer, there is an increase in the risk of stillbirth and neonatal death, a large review of studies has found. 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.

Current practice in the United States is to induce labor at 41 weeks.

The British 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.

The risk of neonatal death did not change between 38 and 41 weeks, but at 41 weeks or more the relative risk of a baby’s death in the first month increased slightly compared with 40 weeks.

“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.”