SAN DIEGO — The risk of neonatal morbidity, particularly of respiratory distress syndrome, is significantly higher for infants born between 34 and nearly 37 weeks' gestation than for those born at term, an analysis of Centers for Disease Control and Prevention data showed.
“We used to think that the lungs of a neonate are mature by 34 weeks, but we found out that's not always the case,” Dr. Amy Flick said in an interview during a poster session at the annual meeting of the Society for Maternal-Fetal Medicine. “If a neonate is [at] 34 weeks' gestational age and is fine, there should be no reason to deliver; you could be risking a bad outcome.”
To compare neonatal morbidity for infants born at 34–36.9 weeks' gestation with that for infants born at 37–42 weeks, and to compare pregnancy outcomes for women in the two groups, Dr. Flick and her associates analyzed data from the 2004 CDC national birth registry. The researchers performed a secondary analysis using 2004 National Center for Health Statistics birth statistical files.
Compared with women whose infants were born at term, the women who bore infants in the late preterm period had significantly higher rates of hypertension (1.8% vs. 0.8%), preeclampsia (7.8% vs. 3.2%), preterm premature rupture of membranes (5.1% vs. 1.2%), and diabetes (5.2% vs. 3.4%), said Dr. Flick of the department of obstetrics and gynecology at the University of Miami.
The risk of neonatal composite morbidity was significantly higher in the late preterm group than in infants born at term (8.9% vs. 3.3%). Logistic regression analysis revealed that infants in the late preterm group were also 5.3 times more likely to have respiratory distress syndrome, 3.7 times more likely to require assisted ventilation, and 1.6 times more likely to have a 5-minute Apgar score of less than 7.
The risks and benefits of even late preterm deliveries must be presented to patients in a comprehensive manner along with input from neonatologists, the investigators concluded. They also called for further studies, including longer follow-up of late preterm infants.
Dr. Flick acknowledged certain limitations of the study, including its retrospective design and the fact that data came from birth certificates.