Timing induction of labour at 41 or 42 weeks? A closer look at time frames of comparison: A review

•Whether induction at 41 weeks should be preferred above induction at 42 weeks is still unclear.•The risk of perinatal mortality between 41 and 42 weeks is low.•The risk on meconium aspiration syndrome between 41 and 42 weeks is still unclear.•There is no difference in Caesarean section rate between induction at 41 or 42 weeks. Background: Postterm pregnancy is associated with increased perinatal risk. The WHO defines postterm pregnancy as a pregnancy at or beyond 42 weeks + 0 days, though currently labour is induced at 41 weeks in many settings. Guidelines on timing of labour induction are frequently based on the Cochrane systematic review ‘Induction of labour for improving birth outcomes for women at or beyond term’ in which is concluded that a policy of induction of labour is associated with fewer adverse perinatal outcome and fewer Caesarean sections. However, the included trials differed regarding the timing of induction, ranging from 39 to beyond 42 weeks while the upper limit of expectant management exceeded a gestational age of 42 weeks in most studies. Objective: to evaluate perinatal mortality, meconium aspiration syndrome and Caesarean section rate of trials comparing a policy of elective induction of labour and expectant management according to timeframes of comparison with a focus on studies within the 41–42 weeks’ timeframe. Design: Review. Methods: The systematic review of Cochrane was used as a starting point for assessing relevant trials and a search was performed for additional recent trials. We evaluated incidence and causes of perinatal mortality, incidence of meconium aspiration syndrome and Caesarean section according to three time frames of comparison. We pooled estimates and heterogeneity was tested. The quality of the included trials was assessed using the Quality Assessment Tool for Quantative Studies (EPHPP). Findings: In total 22 trials were included which had all different timeframes of comparison. Only one trial compared induction of labour at 41 weeks + 0–2 days with induction at 42 weeks + 0 days, three other trials compared induction of labour at 41 weeks + 0–6 days with induction at 42 weeks + 0–6 days. In 18 trials the comparison was outside the 41–42 weeks’ timeframe: in six trials induction was planned ≤ 40 weeks and in another 12 trials expectant management was beyond 43 weeks. The incidence of potentially gestational age associated perinatal mortality between 41 and 42 weeks was 0/2.444 [0%] (induction) versus 4/2.452