Labor Induction at 41 Weeks Tied to Lower Morbidity, Mortality Than Expectant Management

By Lisa Rapaport

January 13, 2021

(Reuters Health) - Inducing labor at 41 weeks may result in a lower risk of severe adverse perinatal and neonatal outcomes than expectant management until 42 weeks, a systematic review and meta-analysis of randomized clinical trials in PLOS Medicine suggests.

Researchers examined data from three clinical trials with a total of 5,161 low-risk singleton pregnancies. They assessed a composite primary outcome of perinatal mortality, including stillbirth or neonatal mortality within 28 days of birth, and neonatal morbidity including: five-minute Apgar score below 4, hypoxic ischemic encephalopathy, intracranial hemorrhage, neonatal convulsions, respiratory distress, mechanical ventilation within 72 hours of birth, and obstetric brachial plexus injury.

The analysis included individual data for 4,561 participants, including 2,281 women scheduled for labor induction at 41 weeks; four in five of these women ultimately had the scheduled induction and the rest delivered spontaneously. Among 2,280 women assigned to expectant management until 42 weeks, about 30% needed induction and the rest delivered spontaneously.

In the induction group, 10 cases (0.4%) met the composite primary endpoint of perinatal death or severe neonatal morbidity; 23 cases (1.0%) occurred in the expectant management group.

"The take home messages is that induction of labor will decrease the risk of adverse perinatal outcome, including mortality, without increasing the morbidity risk for the woman including cesarean delivery, perineal laceration grade III-IV and postpartum hemorrhage -- especially in nulliparous women," said lead study author Dr. Marten Alkmark of the University of Gothenburg in Sweden.

"For parous women the risk of adverse perinatal outcome is very low with both induction of labor and expectant management," Dr. Alkmark said by email.

Among nulliparous women, the risk of the primary outcome was lower among those in the induction group (0.03%) than in the expectant management group (1.6%). However, the risk of the primary outcome among multiparous women was similar with induction (0.6%) and expectant management (0.3%).

None of the women in the study had a history of cesarean delivery or other major uterine surgery, and all of them had low-risk singleton pregnancies with the fetus in cephalic position.

Researchers also looked at perinatal secondary outcomes and found there was only one perinatal death in the induction group, a stillbirth that occurred after randomization but before induction. Seven of the eight perinatal deaths in the expectant management group were stillbirths, while one infant died because of hypoxic ischemic encephalopathy.

Limitations of the analysis include the relatively small size of the study compared with other reviews of induction versus expectant management, as well as some heterogeneity in how the two trials included in the analysis defined some endpoints.

"The risk of perinatal death and severe neonatal morbidity increases gradually after 41 weeks of pregnancy, probably linked to the placenta deteriorating," said Sara Kenyon, a professor of evidence based maternity care at the University of Birmingham in the U.K. who wasn't involved in the study.

"However, it wasn't clear when the optimal time to induce women is and this study suggests that, particularly for nulliparous women, that this is 41 weeks," Kenyon said by email.

SOURCE: PLoS Medicine, online December 8, 2020.