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Shift in Birth Timing Tied to Decline in Birth Weights

Finding largely due to changes in obstetric practices toward cesarean deliveries, inductions from 1990 to 2013

WEDNESDAY, March 4, 2020 (HealthDay News) — If rates of obstetric practices had not changed between 1990 and 2013 to include more cesarean deliveries and inductions, then the average U.S. birth weight likely would have increased over this time, according to research published online Jan. 29 in Demography.

Andrea M. Tilstra and Ryan K. Masters, Ph.D., of the University of Colorado Boulder, used restricted National Vital Statistics System data-linked birth/infant death data (1990 to 2013) to analyze trends in obstetric practices, gestational age distributions, and birth weights among first-birth singletons born to U.S. non-Hispanic white, non-Hispanic black, and Latina women.

The researchers found that between 1990 and 2013, the likelihood of induced labors and cesarean deliveries increased at all gestational ages. The gestational age distribution of U.S. births significantly shifted with births much less likely to occur beyond gestational week 40 and much more likely to occur during weeks 37 to 39. Overall, births occurring at earlier gestational ages from obstetric interventions replaced nearly 18 percent of births from noninduced labor and vaginal delivery at later gestational ages.

“Findings strongly indicate that recent declines in U.S. birth weight were due to increases in induced labor and cesarean delivery at select gestational ages,” the authors write.

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