Induction of labour for post-term pregnancy and risk estimates for intrauterine and perinatal death

Background. Beyond term there is increased risk of intrauterine fetal death (IUFD) and perinatal death, and we aimed to assess this risk beyond 41 weeks and estimate numbers needed to treat to avoid 1 fetal or neonatal death. Design and methods. All singletons births beyond 41 weeks from 1999-2005 registered in the Norwegian Medical Birth Registry were assessed concerning IUFD and perinatal death day by day, and numbers needed to induce to avoid 1 death was estimated. Results. The perinatal death rate increased with increasing gestational age. NNT for perinatal death was 527 at day 287, and 195 at day 302+ (p-value=0.02). Routine induction of labour at 41 weeks implicates >14,000 inductions per year. Conclusions. NNT to avoid 1 fetal or neonatal death is high (671-195), but decreases constantly with gestational age beyond 41 weeks.