Most people know that preterm birth is a major contributor to perinatal morbidity and mortality. Consequently, strict guidelines have been enforced to prevent non–medically indicated scheduled deliveries before 39 weeks’ gestation. Fewer people recognize that late-term birth is also an important and avoidable contributor to perinatal morbidity. To improve pregnancy outcomes, we may need enhanced guidelines about minimizing expectant management of pregnancy beyond 41 weeks’ gestation.
For the fetus, what is the optimal duration of a healthy pregnancy?
When pregnancy progresses past the date of the confinement, the risk of fetal or newborn injury or death increases, especially after 41 weeks’ gestation. Analysis of this risk, day by day, suggests that after 40 weeks’ and 3 days’ gestation there is no medical benefit to the fetus to remain in utero because, compared with induced delivery, expectant management of the pregnancy is associated with a greater rate of fetal and newborn morbidity and mortality.1
The fetal and newborn benefits of delivery, rather than expectant management, at term include: a decrease in stillbirth and perinatal death rates, a decrease in admissions to the neonatal intensive care unit (NICU), a decrease in meconium-stained amniotic fluid and meconium aspiration syndrome, a decrease in low Apgar scores, and a decrease in problems related to uteroplacental insufficiency, including oligohydramnios.2 In a comprehensive meta-analysis, induction of labor at or beyond term reduced the risk of perinatal death or stillbirth by 67%, the risk of a 5-minute Apgar score below 7 by 30%, and the risk of NICU admission by 12%.2 The number of women that would need to be induced to prevent 1 perinatal death was estimated to be 426.2
Maternal benefits of avoiding late-term pregnancy
The maternal benefits of avoiding continuing a pregnancy past 41 weeks’ gestation include a reduction in labor dystocia and the risk of cesarean delivery (CD).2,3 In one clinical trial, 3,407 women with low-risk pregnancy were randomly assigned to induction of labor at 41 weeks’ gestation or expectant management, awaiting the onset of labor with serial antenatal monitoring (nonstress tests and assessment of amniotic fluid volume).4 The CD rate was lower among the women randomized to induction of labor at 41 weeks’ (21.2% vs 24.5% in the expectant management group, P = .03). The rate of meconium-stained fluid was lower in the induction of labor group (25.0% vs 28.7%, P = .009). The rate of CD due to fetal distress also was lower in the induction of labor group (5.7% vs 8.3%, P = .003). The risks of maternal postpartum hemorrhage, sepsis, and endometritis did not differ between the groups. There were 2 stillbirths in the expectant management group (2/1,706) and none in the induction of labor group (0/1,701). There were no neonatal deaths in this study.4
Obstetric management, including accurate dating of pregnancy and membrane sweeping at term, can help to reduce the risk that a pregnancy will progress beyond 41 weeks’ gestation.5
Continue to: Routinely use ultrasound to accurately establish gestational age