Delivery at 37 Weeks vs 40 Weeks: Evidence-Based Recommendations
For uncomplicated pregnancies without medical indications, delivery should occur at 39-40 weeks gestation, not at 37 weeks, as early-term delivery (37-38 weeks) is associated with increased neonatal morbidity, mortality, and long-term neurodevelopmental impairment compared to full-term delivery at 39 weeks or beyond. 1, 2
General Principles for Uncomplicated Pregnancies
Nonmedically indicated deliveries before 39 0/7 weeks should be avoided because neonates delivered in the early-term period (37 0/7 to 38 6/7 weeks) have significantly higher rates of adverse outcomes including respiratory complications, NICU admissions, hypoglycemia, and feeding difficulties compared to those delivered at 39 weeks or later. 1, 2
Long-term outcomes are also compromised with early-term delivery, as children born at 37-38 weeks demonstrate lower performance scores across cognitive and educational measures compared to their full-term peers delivered at 39 weeks or beyond. 1, 2
Fetal lung maturity testing should not guide delivery timing even in suboptimally dated pregnancies, as documentation of pulmonary maturity alone does not indicate that other fetal physiologic processes are adequately developed. 1, 2
Medical Indications That Justify Early-Term Delivery at 37 Weeks
The decision to deliver at 37 weeks versus waiting until 39-40 weeks depends entirely on specific maternal or fetal conditions. The following conditions warrant delivery at 37 weeks:
Fetal Growth Restriction (FGR)
Deliver at 37 weeks for FGR with abnormal umbilical artery Doppler showing decreased diastolic flow (S/D, RI, or PI >95th percentile) but without absent or reversed end-diastolic velocity. 3
Deliver at 37 weeks for severe FGR with estimated fetal weight <3rd percentile, regardless of Doppler findings. 3
For FGR with normal Doppler studies and EFW between 3rd-10th percentile, delivery at 38-39 weeks is appropriate. 3, 4
Intrahepatic Cholestasis of Pregnancy (ICP)
Deliver between 36 0/7 and 39 0/7 weeks for ICP with total bile acid levels <100 μmol/L, with timing individualized based on bile acid levels—those with levels <40 μmol/L can be managed toward 39 weeks, while those with levels 40-99 μmol/L should be considered for earlier delivery around 37 weeks. 3
Deliver at 36 0/7 weeks for ICP with total bile acid levels ≥100 μmol/L due to substantially increased stillbirth risk. 3
Do not deliver before 37 weeks without laboratory confirmation of elevated bile acids, even if clinical suspicion is high. 3
Gestational Diabetes
Deliver at 38 weeks for diet-controlled gestational diabetes. 4
Deliver by 39 weeks for medication-dependent gestational diabetes. 4
Placenta Accreta Spectrum
- Scheduled delivery at 34 0/7 to 35 6/7 weeks is preferred for placenta accreta spectrum in stable patients, as this balances neonatal outcomes with maternal hemorrhage risk that increases significantly after 36 weeks. 3
Critical Considerations When Delivery Before 39 Weeks Is Indicated
Antenatal corticosteroids must be administered if delivery will occur before 37 0/7 weeks and has not been previously given. 3
Accurate pregnancy dating is imperative to avoid iatrogenic early-term or preterm delivery—this requires confirmation with early ultrasound (before 21 weeks) rather than relying solely on last menstrual period. 4
The decision must balance pregnancy prolongation risks against neonatal risks of early delivery, recognizing that deferring delivery to 39 weeks is not recommended when clear medical or obstetric indications exist for earlier delivery. 5, 2
Common Pitfalls to Avoid
Do not perform elective delivery at 37-38 weeks without medical indication, as this increases neonatal morbidity without maternal or fetal benefit. 6, 1, 2
Do not use lung maturity testing to justify early-term delivery, as mature lungs do not guarantee maturity of other organ systems. 1, 2
Do not delay medically indicated delivery to 39 weeks when conditions like severe FGR, high bile acids in ICP, or placenta accreta spectrum warrant earlier intervention—the risks of expectant management outweigh the risks of early delivery in these scenarios. 5, 2
Ensure documentation of the medical indication for any delivery before 39 weeks, as some payers have stopped reimbursement for nonindicated early deliveries. 6