Perinatal morbidity associated with late preterm deliveries compared with deliveries between 37 and 40 weeks of gestation

Objective To estimate the risk of short-term complications in neonates born between 34 and 36 weeks of gestation. Design This is a retrospective cohort study. Setting Deliveries in 2005 in the USA. Population Singleton live births between 34 and 40 weeks of gestation. Methods Gestational age was subgrouped into 34, 35, 36 and 37-40 completed weeks of gestation. Statistical comparisons were performed using chi-square test and multivariable logistic regression models, with 37-40 weeks of gestation designated as referent. Main outcome measures Perinatal morbidities, including 5-minute Apgar scores, hyaline membrane disease, neonatal sepsis/antibiotics use, and admission to the intensive care unit. Results In all, 175 112 neonates were born between 34 and 36 weeks in 2005. Compared with neonates born between 37 and 40 weeks, neonates born at 34 weeks had higher odds of 5-minute Apgar <7 (adjusted odds ratio [aOR] 5.51, 95% CI 5.16-5.88), hyaline membrane disease (aOR 10.2, 95% CI 9.44-10.9), mechanical ventilation use >6 hours (aOR 9.78, 95% CI 8.99-10.6) and antibiotic use (aOR 9.00, 95% CI 8.43-9.60). Neonates born at 35 weeks were similarly at risk of morbidity, with higher odds of 5-minute Apgar <7 (aOR 3.42, 95% CI 3.23-3.63), surfactant use (aOR 3.74, 95% CI 3.21-4.22), ventilation use >6 hours (aOR 5.53, 95% CI 5.11-5.99) and neonatal intensive-care unit admission (aOR 11.3, 95% CI 11.0-11.7). Neonates born at 36 weeks remain at higher risk of morbidity compared with deliveries at 37-40 weeks of gestation. Conclusions Although the risk of undesirable neonatal outcomes decreases with increasing gestational age, the risk of neonatal complications in late preterm births remains higher compared with infants delivered at 37-40 weeks of gestation.