If your pregnancy runs past its due date, how long should you wait for a natural birth? It may be safer to induce at 40 weeks, for older mums at least
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If your pregnancy runs past its due date, how long should you wait before being induced? Evidence is building that, at least for older women, it’s safer to get the baby out on time, at 40 weeks.
This seems to be the case for first-time mums, according to a review of 80,000 women in England. Gordon Smith of the University of Cambridge and his colleagues found that when women aged 35 or older are induced at 40 weeks, only 0.08 per cent of their babies died. But in women who waited until they gave birth naturally, or who were induced at 41 to 42 weeks, this rose to 0.26 per cent.
This means that, for every 562 women who were induced at 40 weeks, one stillbirth was avoided.
After a certain point, the longer a pregnancy continues, the more likely it is that a baby will die unexpectedly in the womb – probably because it gets too big to be supported by a deteriorating placenta. By 40 weeks, the placenta is beginning to fail, says Smith.
Birth can be triggered with medicines that open the cervix and bring on contractions, but this tends to make labour longer and more painful. Induction is currently recommended in the UK if a woman has gone overdue by one to two weeks, regardless of her age.
The team found that earlier inductions tended to have a slightly higher rate of emergency Caesarean sections and the use of instruments like forceps. But this could have been because women with complications were more likely to be induced early, says Smith.
Last year a randomised trial found inducing over-35s even earlier, at 39 to 40 weeks, made no difference to the rate of C-sections or instrumental deliveries.
Smith says women should be told about the pros and cons of induction and offered a choice. “The absolute risk [of waiting] is small. For some women it’s acceptable in the context of prioritising a natural approach. For others it’s unacceptable.”
Women are tending to have children later in life in the UK, says Hannah Knight of the London School of Hygiene and Tropical Medicine, who also worked on the study. About one in seven first-time mothers were 35 or older in England and Wales in 2015.
Smith says younger women might also consider an earlier induction based on these findings. “It’s self-evident that if you deliver the baby at 40 weeks, it cannot be stillborn at 41 weeks.”
Journal reference: Plos Medicine, DOI: 10.1371/journal.pmed.1002425
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