What are the pros and cons of delivering a baby at 39 weeks gestation versus 40 weeks?

From the Guidelines

Delivering a baby at 39 weeks gestation is a reasonable and safe option for low-risk nulliparous women, as it has been shown to have favorable outcomes, including reduced rates of primary cesarean delivery and hypertensive disorders of pregnancy, as demonstrated in the ARRIVE trial 1. When considering the pros and cons of delivering a baby at 39 weeks gestation versus 40 weeks, several factors come into play. The benefits of delivery at 39 weeks include:

• Reduced risks of stillbirth, which increases slightly each week after 39 weeks
• Decreased likelihood of needing cesarean delivery due to fetal size
• Lower rates of meconium aspiration
• Less discomfort from late-pregnancy symptoms for mothers However, waiting until 40 weeks allows the baby additional time for brain development and weight gain, which can be beneficial. Some key points to consider are:
• The ARRIVE trial found no statistically significant difference in primary perinatal outcomes between elective induction of labor (IOL) and expectant management in low-risk nulliparous women at 39 weeks of gestation 1
• The trial did find notable reductions in the rate of primary cesarean delivery and in hypertensive disorders of pregnancy with elective IOL 1
• The American Journal of Obstetrics and Gynecology published a statement on elective induction of labor in low-risk nulliparous women at term, which supports the idea that elective IOL at 39 weeks is a reasonable option 1
• It is essential to individualize the decision based on maternal health factors, fetal well-being, and personal preferences in consultation with healthcare providers. Ultimately, the decision to deliver a baby at 39 weeks or 40 weeks should be made on a case-by-case basis, taking into account the unique circumstances of each pregnancy. The current evidence suggests that elective induction of labor at 39 weeks is a safe and reasonable option for low-risk nulliparous women, and it may be beneficial in reducing the risk of certain complications 1.

From the Research

Comparison of Delivery at 39 Weeks and 40 Weeks Gestation

• The optimal timing for induction of labor at term in gestational diabetes appears to be 39 to 40 weeks, as found in a study published in 2015 2.
• A study from 2014 found that 8.5% of low-risk women planned for repeat caesarean section went into spontaneous labor before 39 weeks, with the risk varying depending on previous delivery history and other factors 3.
• Recent studies have shown that elective induction of labor versus expectant management after 39 weeks of pregnancy result in lower incidence of perinatal complications, while the proportion of cesarean deliveries remains stable, or even decreases 4.
• A 2020 Cochrane Review found that a policy of labor induction at or beyond 37 weeks' gestation compared with expectant management was associated with fewer perinatal deaths, stillbirths, and cesarean sections, as well as lower rates of neonatal intensive care unit admission 5.
• A study from 2000 found that labor complications increased from 40 to 42 weeks, including oxytocin induction, length of labor, and cesarean delivery, while neonatal outcomes were similar in the three groups 6.

Pros of Delivering at 39 Weeks

• Lower risk of perinatal complications and stillbirths 4, 5
• Possibly lower risk of cesarean section 5
• Lower risk of labor complications compared to delivering at 40 weeks or later 6

Cons of Delivering at 39 Weeks

• Possibly higher risk of neonatal intensive care unit admission compared to delivering at 40 weeks 6
• May not be suitable for all women, particularly those with gestational diabetes or other complications 2
• Requires careful consideration of individual risk factors and medical history 3, 5