Large Study Assesses Recent Data on Respiratory Morbidity in Late Preterm Neonates

Emma Hitt, PhD

September 18, 2010

July 27, 2010 — Respiratory morbidity rate in infants born during the late preterm period is substantially increased vs infants born at term, according to the largest investigation to date on the issue.

Judith U. Hibbard, MD, with the Department of Obstetrics and Gynecology at the University of Illinois at Chicago, and colleagues from the Consortium on Safe Labor reported the findings in the July 28, 2010, issue of the Journal of the American Medical Association.

According to the researchers, late preterm births (spanning from 34 weeks and 0 days to nearly 37 weeks of gestation) account for 9.1% of all deliveries and approximately 75% of all preterm births in the United States. Preterm deliveries are known to be associated with increased respiratory morbidity rates, but recent data from a large, US-based study are lacking.

"Given advances in obstetric and neonatal care over the last 20 years, we hypothesized that many published rates of morbidity may overestimate the clinical burden attributable to late preterm birth," the study authors note.

The researchers assessed short-term respiratory morbidity in 19,334 late preterm births and compared it with that of 165,993 term births in a contemporary cohort of deliveries in the United States.

Of the late preterm infants, 36.5% were admitted to a neonatal intensive care unit (NICU), and approximately one third of those had respiratory tract symptoms. By contrast, only 7.2% of the term infants were admitted to a NICU, and less than 10% of those had respiratory tract symptoms.

The incidence of respiratory distress syndrome was 10.5% for infants born late preterm (34 weeks of gestation) vs 0.3% for those born at term (38 weeks). Likewise, in late preterm births vs term births, transient tachypnea of the newborn was present in 6.4% vs 0.4%, pneumonia in 1.5% vs 0.1%, and respiratory failure in 1.6% vs 0.2%. Standard and oscillatory ventilatory support was also more common in late preterm births vs term births.

The risk for respiratory distress syndrome was much higher at 34 weeks of gestation (adjusted odds ratio [OR], 40.1; 95% confidence interval [CI], 32.0 - 50.3) vs 38 weeks of gestation (adjusted OR, 1.1; 95% CI, 0.9 - 1.4). At 37 weeks, the adjusted OR for respiratory distress syndrome was higher at 3.1 (95% CI, 2.5 - 3.7) vs 39 and 40 weeks. For infants born at 38 weeks, the risk for any respiratory morbidity was approximately the same at it was for infants born at 39 or 40 weeks.

Risk for other respiratory disorders, including transient tachypnea of the newborn, pneumonia, and respiratory failure also followed a similar pattern of decreasing with gestational age.

"The results of our study support the recommendation that every effort should be made to delay delivery of infants until at least 38 weeks' gestational age to decrease respiratory morbidity," Dr. Hibbard and colleagues conclude.

This study was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health. The study authors have disclosed no relevant financial relationships.

JAMA. 2010;304:419-425.

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