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



This article is corrected by:

  1. Errata: Errata Volume 118, Issue 13, 1687, Article first published online: 11 November 2011

Dr YW Cheng, Division of Maternal–Fetal Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, 505 Parnassus Avenue Box 0132, San Francisco, CA 94143-0132, USA. Email


Please cite this paper as: Cheng Y, Kaimal A, Bruckner T, Hallaron D, Caughey A. Perinatal morbidity associated with late preterm deliveries compared with deliveries between 37 and 40 weeks of gestation. BJOG 2011;118:1446–1454.

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.