Labor induction at 40 weeks associated with lower risk of perinatal mortality

Guidelines recommend induction of labor between 41 and 42 weeks of gestation to prevent the risks associated with prolonged pregnancy. Women having their first baby at age 35 years or over are at increased risk of pregnancy complications, including perinatal death. To better understand the risks and benefits of elective induction in this group, Knight and colleagues analyzed a national dataset of 77,327 such mothers giving birth between 2009 and 2014. They found that induction of labor at 40 weeks (compared with expectant management) was associated with a lower risk of in-hospital perinatal death (0.08% versus 0.26%; adjusted risk ratio [adjRR] 0.33; 95% confidence interval [CI] 0.13-0.80, P = 0.015) and meconium aspiration syndrome (0.44% versus 0.86%; adjRR 0.52; 95% CI 0.35-0.78, P = 0.002). Induction at 40 weeks was also associated with a slightly increased adjusted risk of instrumental vaginal delivery (adjRR 1.06; 95% CI 1.01-1.11, P = 0.020) and emergency caesarean section (adjRR 1.05; 95% CI 1.01-1.09, P = 0.019). The number needed to treat (NNT) analysis indicated that 562 (95% CI 366-1,210) inductions of labor at 40 weeks would be required to prevent 1 perinatal death.

Unmeasured confounding may have influenced these results, and inductions and/or outcomes may have been under-recorded in the database. However, this association provides evidence that, as the authors state, "[b]ringing forward the routine offer of induction of labour from the current recommendation of 41-42 weeks to 40 weeks of gestation in this group of women may reduce overall rates of perinatal death."