Induction at 41 weeks: Are we overestimating the benefit?

Abstract

Sir,

With great interest, we read the paper by Ravelli et al., published in Acta Obstetricia et Gynecologica Scandinavica.¹ The study demonstrated a reduced stillbirth rate following induction of labor (IOL) from 41 weeks onwards, compared to expectant management (EM). In addition, it reported a higher incidence of low Apgar score, NICU admissions and increased cesarean section rates.

We acknowledge the importance of the topic, particularly as IOL at 41 weeks is routinely offered in many countries. However, it is important to note that the perinatal mortality rate may have been overestimated in the EM group due to differences in how stillbirths were included in the two groups. Specifically, stillbirths were excluded from the IOL group but not consistently from the EM group.

We believe that the construction of the EM group may have introduced a slight but important overestimation of stillbirths. In the study, IOL at 41+0/41+1 weeks was compared with spontaneous onset between 41+0 and 42+0, or IOL between 41+3 and 42+0. Since IOL is offered after stillbirth, all stillbirths were excluded from the IOL group. However, women who had a planned IOL at 41+0/41+1 weeks but experienced a stillbirth along with a spontaneous onset before IOL were assigned to the EM group. To ensure comparability between the groups and avoid overestimation of perinatal mortality in the EM group, stillbirths occurring in the first 2 days (i.e. before scheduled IOL) should have been excluded, as was done in the IOL group.

More importantly, we would like to highlight the high number needed to treat (NNT) for IOL to prevent one perinatal death. In the study by Ravelli et al., the perinatal mortality rate was 0.07% (27/21 963) in the IOL group (41+0/41+1 weeks) versus 0.12% (15/21 963) in the EM group, resulting in a NNT of 1830. This means that 1830 women would need to undergo IOL to prevent one perinatal death. This is substantially higher than the NNT of 326 reported in the meta-analysis by Alkmark et al.,² which is currently used to inform pregnant women.

Furthermore, Ravelli et al. showed that IOL did not lead to a significant reduction in perinatal mortality at 41+0/41+1 weeks. The difference became significant from 41+2/41+3 weeks onwards. This finding was consistent across both nulliparous and multiparous women. Considering the aforementioned methodological limitations, it is plausible that the actual NNT is even higher, given the likely overestimation of mortality in the EM group. Additionally, the higher rates of low Apgar score, NICU admissions and cesarean sections suggest that the disadvantages of IOL after 41 weeks may be more substantial than currently communicated to pregnant women.

It is concerning that many women are currently opting for IOL at 41+0 weeks based on data from a meta-analysis that may overestimate the benefits of IOL. We therefore recommend reviewing current guidelines recommending routinely offering IOL at 41+0 weeks to all healthy women and incorporating the valuable findings from this study that the actual NNT appears to be much higher than previously assumed.