Post-term pregnancy: should induction of labor be considered before 42 weeks?

To determine the occurrence of maternal and fetal complications in low-risk pregnancies beyond 39 weeks and to re-evaluate the acceptable cut-off (42 weeks) for induction of labor.

A total of 36 160 low-risk pregnancies with reliable dating of gestational age (last menstrual period and early ultrasound examination) were evaluated retrospectively for fetal and maternal complications, including non-progressive labor, cervical tear, retained placenta, postpartum hemorrhage, vacuum delivery, Cesarean section, macrosomia, meconium-stained amniotic fluid, non-reassuring fetal heart rate monitoring and ante-, intra- and postpartum death. Pregnancy outcomes at different gestational ages were compared using univariate and multivariate analysis and receiver operator curves.

The rates of non-progressive labor stage I and II, retained placenta, vacuum delivery, Cesarean section, macrosomia, meconium-stained amniotic fluid and non-reassuring fetal heart rate monitoring were found to be significantly higher with increasing gestational age in the univariate analysis. These parameters were evaluated using multivariate analysis and the following were found to be significantly higher: non-progressive labor stage I and II, macrosomia, meconium-stained amniotic fluid and Cesarean section. Statistical analysis (receiver operator curves) showed that the most significant rise in the risk for non-progressive labor occurred after 42 completed weeks of gestation, and after 41 completed weeks for macrosomia, meconium-stained amniotic fluid and Cesarean section.

The rates of non-progressive labor stage I and II, meconium-stained amniotic fluid, macrosomia and Cesarean section were significantly higher with increasing gestational age. In order to decrease the rate of macrosomia, meconium-stained amniotic fluid and Cesarean section, we suggest that induction of labor should be considered before 42 weeks.