This article is more than 5 years old. Information may no longer be current.
U.S. birth weights on the decline
Click Here to Manage Email Alerts
New data suggest that birth weights in the United States have declined during the past 15 years.
Researchers analyzed data on birth weight, maternal and neonatal characteristics, obstetric care and other trends from the U.S. National Center for Health Statistics Natality Data Sets on 36.8 million babies. All babies were born at full-term between 1990 and 2005.
Analysis revealed that birth weights decreased by an average of 52 g (1.83 oz) between 1990 and 2005. Further, large for gestational age births also decreased (–1.4% overall). According to the researchers, the decreases were steeper after 1999 and persisted after the researchers adjusted for maternal and neonate characteristics such as gestational length, induction of labor and cesarean delivery.
In contrast to previous findings, birth weights lowered even further in infants born to a subset of women considered to be at low risk for small babies; mothers who were white, well-educated, married, did not smoke, received early prenatal care and delivered vaginally with no complications had babies who weighed an average 79 g (2.78 oz) less at birth.
The researchers also noted a decrease in mean gestational length (–0.34 weeks overall) regardless of induction of labor or route of delivery.
The causes of the declines remain unclear and were “not explained by trends in maternal and neonatal characteristics, changes in obstetric practices or concurrent decreases in gestational length,” according to the researchers.
However, although the decline may simply represent a reversal of previous increases in birth weights, it may also indicate short-term complications for babies born small, such as increased likelihood of requiring intensive care after birth, higher risk for mortality and risk for chronic diseases in adulthood.
Future research may identify other factors not included in the current analysis such as trends in mothers’ diets, physical activity, stress and exposure to environmental toxins, the researchers said.
Donahue SMA. Obstet Gynecol. 2010;115:357-364.