Foeto–Maternal outcomes of pregnancies beyond 41 weeks of gestation after induced or spontaneous labour

Objective

It has been suggested that induction of labour before 42 weeks of pregnancy prevents foetal complications. To evaluate the maternal and foetal outcomes of induced and spontaneous labour beyond gestational week 41 + 0.

Study design

We conducted a register-based nationwide cohort study that included pregnant women who were delivered in Sweden in 2016–2021. Women were classified into two groups: induction of labour (IOL) or spontaneous onset of labour (SOL). Maternal and foetal outcomes after IOL in gestational week 41 were compared with SOL in gestational week 41 and 42.

Results

Comparison between the IOL (n = 23,772) and SOL (n = 62,611) groups in gestational weeks 41 showed that various parameters were higher in the IOL group: caesarean deliveries (12.3 % and 4.6 %, P < 0.001), vacuum extraction (8.7 % and 6.9 %, P < 0.001), blood loss of > 1000 ml during labour (11 % vs 8.3 %, P < 0.001). The risks were remained significant even after adjusting for potential confounders (caesarean delivery: aOR 2.36; 95 % CI, 2.23–2.50, vacuum delivery: aOR 1.09; 95 % CI, 1.03–1.16, P = 0.002, and blood loss of >1000 ml: aOR 1.25; 95 % CI 1.18–1.31). The proportions of stillbirths (0.07 % and 0.18, P < 0.001), and newborns with apgar scores < 4 at five minutes (0.4 % vs 0.3 %, P < 0.001), were also higher in the IOL group. The risk of stillbirth after IOL in gestational week 41 was increased relative to SOL in the same week and remained high after adjusting for potential confounders (aOR 1.75; 95 % CI 1.07–2.80, P = 0.025).

The IOL group in gestational weeks 41 comprised a higher proportion of caesarean deliveries (12.3 % and 8.5 %, P < 0.001), but a lower (8.7 % and 9.7 %, P = 0.006) proportion of deliveries by vacuum extraction than the SOL group (n = 4548) in week 42.

Conclusions

Inducing labour at gestational week 41 in women with prolonged pregnancies may have adverse effects on foetal and maternal outcomes compared to those who experience spontaneous labour onset at the same gestational age. The risk of negative foetal outcomes after induction at week 41 appears similar to that in women who give birth after spontaneous labour at week 42.