What are the risks of delivering at 38 weeks versus 39 weeks?

From the Guidelines

Delivering a baby at 38 weeks carries slightly higher risks compared to waiting until 39 weeks, and it is recommended to wait until at least 39 weeks for elective deliveries unless there are specific medical indications for earlier delivery. Babies born at 38 weeks have increased chances of respiratory problems, including transient tachypnea of the newborn and respiratory distress syndrome, as lung development continues to mature in the final weeks of pregnancy 1. They may also face higher rates of NICU admission, feeding difficulties, jaundice, and temperature regulation issues. Cognitively, there is evidence suggesting slightly lower long-term academic performance and higher rates of developmental issues in children born at 38 weeks versus 39 weeks. For the mother, there is no significant difference in delivery complications between these gestational ages.

Key Considerations

• The American College of Obstetricians and Gynecologists recommends waiting until at least 39 weeks for elective deliveries because this extra week allows for important brain, lung, and liver development 1.
• The brain increases in weight by about one-third between 35 and 39 weeks, and important neural connections form during this time.
• Unless there are specific medical indications for earlier delivery such as preeclampsia, gestational diabetes with complications, or fetal growth restriction, the benefits of waiting until 39 weeks generally outweigh the risks of delivering at 38 weeks 1.
• Antenatal corticosteroids may be considered for women delivering by elective caesarean section at ≤38 weeks’ gestation to reduce respiratory morbidity 1.

Risks and Benefits

• Delivering at 38 weeks versus 39 weeks entails a small absolute but substantially increased risk of development of infant respiratory distress requiring mechanical ventilation 1.
• The decision for delivery should be based on the entire clinical scenario, including fetal and maternal factors, and should involve coordination of care between maternal-fetal medicine and neonatology services 1.

From the Research

Risks of Delivering at 38 Weeks vs 39 Weeks

• Delivering a baby at 38 weeks instead of 39 weeks may be associated with increased neonatal risks, including higher infant mortality and increased risk of impairments after birth 2.
• The risks of various complications are disproportionately more pronounced the earlier the child is delivered, with the risk of needing respiratory support or artificial ventilation after birth increasing from 0.3% with delivery at 39-41 weeks of gestational age to 1.4% at 37 weeks and 10% at 35 weeks 2.
• However, deferring delivery to the 39th week is not recommended if there is a medical or obstetric indication for earlier delivery, and the timing of delivery must balance the maternal and newborn risks of late-preterm and early-term delivery with the risks associated with further continuation of pregnancy 3, 4.
• Studies have shown that the number of medically indicated deliveries before 39 weeks can be lowered by 70% to 80% through consistently applied measures for quality improvement, which could reduce the risks of iatrogenic complications of delivery 2.
• For women with hypertensive disorders, clinician-initiated delivery at 34-38 weeks' gestation may be associated with increased risk of adverse maternal and infant outcomes, but the risk differences decrease as gestational age approaches 37 weeks 5.

Specific Risks Associated with Early Delivery

• Increased risk of respiratory support or artificial ventilation after birth 2
• Increased risk of death or neurological complications 2
• Increased risk of cerebral palsy, with a threefold increase in frequency compared to delivery at term 2
• Increased risk of dependence on government benefits in early adulthood 2
• Increased risk of adverse infant health consequences, including Neonatal Intensive Care Unit admission and infant hospital stay 5