Rates of intrauterine fetal demise and neonatal morbidity at term: determining optimal timing of delivery.

Objective: To examine rates of unexplained intrauterine fetal demise (IUFD) and neonatal morbidity in uncomplicated term pregnancies to identify the optimal gestational age for delivery.

Methods: A retrospective case control study was performed with singleton pregnancies delivered between 37 0/7 weeks and 42 6/7 weeks. Exclusion criteria were "complicated pregnancies": emergency deliveries, maternal hypertension, diabetes, infection, fetal disease/malformations and placental abnormalities.

Results: Nineteen thousand two hundred and sixty-four maternal/infant pairs were examined. The overall rate of NICU admission was 2.7% and the rate of unexplained IUFD was 2.02 per 1000 births. The lowest rate of IUFD was found at 39 weeks (1.40 per 1000 births). Odds ratios adjusted for maternal smoking, ethnicity, age and mode of delivery showed 2.74 (95% CI 0.35-21.83) risk of IUFD at 42 versus 39 weeks, 2.09 (1.47-2.98) risk of NICU admission at 37 versus 38 weeks, 2.54 (1.62-3.97) risk of respiratory morbidity at 37 versus 38 weeks and 3.38 (1.84-6.18) risk of transient tachypnea of the newborn or respiratory distress syndrome at 37 versus 38 weeks.

Conclusions: Neonatal respiratory morbidity was lowest for deliveries at 38-39 weeks. IUFD was 2.74 times more likely at 42 weeks versus 39 weeks. Our findings support current guidelines advising clinicians when to deliver term pregnancies.