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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. [ABSTRACT FROM AUTHOR]

Objective: To examine the association between county‐level caesarean delivery (CD) rates among women at low risk and morbidity among term newborns. Design: Cross‐sectional study. Setting: Population‐based study of US county‐level birth data from 2015 to 2017. Population: Nulliparous women with term, singleton, vertex‐presenting infants (NTSV) at low risk for morbidity. Methods: The primary exposure was county‐level CD rates. Main outcome measures: The outcome was morbidity among the low‐risk NTSV cohort, categorised as severe (5‐minute Apgar score of ≤3, assisted ventilation for ≥6 hours, severe neurologic injury or seizure, transfer or death) or moderate (5‐minute Apgar score of <7 but >3, administration of antibiotics or assisted ventilation at delivery). We used linear regression models to determine the association between county NTSV CD and neonatal morbidity rates with cluster robust standard errors. Results: The analysis included data from 2 753 522 births in 952 counties from all 48 states. The mean NTSV CD rate was 23.6% (standard deviation 4.8%). The median severe and moderate neonatal morbidity rates were 15.2 (interquartile range, IQR 9.4–23.6) and 52.5 (IQR 33.4–75.7) per 1000 births, respectively. In the unadjusted analysis using the risk‐adjusted exposure and outcome, every percentage point increase in the CD rate of a county was associated with 0.6 (95% CI −0.9, −0.3) and 2.3 fewer (95% CI −3.4, −1.1) cases of severe and moderate neonatal morbidity per 1000 live births. After adjustment for other county factors, the relationships remained significant. These findings were tested in multiple sensitivity analyses. Conclusions: Lower county‐level NTSV CD rates were associated with a small increase in morbidity among term newborns in the USA. Lower county‐level caesarean delivery rates were associated with an increase in morbidity among term newborns in the USA. Lower county‐level caesarean delivery rates were associated with an increase in morbidity among term newborns in the USA. [ABSTRACT FROM AUTHOR]