Rates of late preterm (34-36 weeks) and early preterm (37-38 weeks) births declined significantly in the United States between 2006 and 2014, according to a report published online July 26 in JAMA.

To examine temporal trends in early birth rates, investigators analyzed data in birth registries for six high-income Western countries, including the United States. They focused on singleton live births delivered at 22 or more weeks’ gestation in which the neonates weighed 500 g or more that occurred between 2006 and the most recent year for which data were available for each country. The study included more than 25.7 million U.S. births, 2.4 million in Canada, approximately 306,000 in Denmark, approximately 572,000 in Finland, approximately 469,000 in Norway, and approximately 738,000 in Sweden, Jennifer L. Richards, MPH, of the department of epidemiology, Emory University, Atlanta, and her associates reported.

During the study period, rates of late preterm birth significantly decreased from 6.8% to 5.7% in the United States and from 3.9% to 3.5% in Norway but remained essentially stable in the other countries. Rates of early term birth also decreased significantly from 31.2% to 24.4% in the United States, from 17.6% to 16.8% in Norway, and from 19.5% to 18.5% in Sweden but remained essentially constant in the other countries. The rates were adjusted for mother’s age at delivery and parity (JAMA. 2016;316[4]:410-9. doi:10.1001/jama.2016.9635).

Ms. Richards and her associates attempted to determine whether declining rates in early births correlated with declines in obstetric interventions, specifically labor inductions and prelabor cesarean deliveries, but they found only one such correlation, in the rate of early term births in the United States. Overall, the rates of clinician-initiated obstetric intervention declined from 48.9% in 2006 to 38.7% in 2014 among U.S. early term births. In all other cases, trends in obstetric interventions varied widely over time and from one country to the next. In addition, rates of late preterm and early term births in the United States declined comparably among deliveries in which there were no obstetric interventions, they noted.

The study was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Paris Descartes University, the Japan Society for the Promotion of Science, and the Japan Ministry of Health, Labour, and Welfare. Ms. Richards reported having no financial disclosures; an associate reported receiving grants from the Uehara Memorial Foundation, the Kanzawa Medical Research Foundation, and the Danone Institute.


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