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U.S. Birth Weights Show Decline During Recent Period

Decrease among singletons not linked to maternal, neonatal factors or trends in induction

WEDNESDAY, Jan. 27 (HealthDay News) -- Birth weights among term births have declined in the United States in recent years, a trend not explained by maternal or neonatal factors or changes in induced labor or Caesarean delivery, according to research published in the February issue of Obstetrics & Gynecology.

Sara M.A. Donahue, of the Boston University School of Public Health, and colleagues analyzed data from the National Center for Health Statistics on more than 36 million singleton births from 1990 to 2005. All were born between 37 and 41 weeks of gestation.

During this period, the researchers found that birth weight decreased by 52 grams overall, while births that were large for gestational age fell by 1.4 percent. Among a subgroup of women considered low-risk by a variety of socioeconomic, demographic and other factors, these decreases were 79 grams and 2.2 percent, respectively. The findings remained after adjustment for gestational length, Caesarean delivery, and other factors.

"Size at birth predicts not only short-term complications but also long-term health and chronic disease risk even among term births. Although the consequences of the modest differences over time in birth weight for gestational age that we observed here are uncertain, any underlying reasons for such a decline may themselves directly influence child health. Therefore, active investigation into the determinants and longer-term sequelae of declining fetal growth among term births is warranted," the authors conclude.

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