Researchers Puzzled by Trend of Lower Birth Weights in U.S.

Wall St. Journal: Birth Weights Fell From 1990 to 2005, by Shirley S. Wang:

Researchers Can't Explain the Two-Ounce Decline in U.S., Worry the Trend Could Lead to Increase in Health Problems

Mothers are giving birth to lighter babies in the U.S., and no one is quite sure why.

The finding, published Thursday in the Journal of Obstetrics and Gynecology, has potentially troubling public-health implications, if the trend continues. Low-birth-weight babies are at higher risk for a host of health problems.

Between 1990 and 2005, the birth weight of full-term babies in the U.S. declined nearly two ounces to an average of 7 pounds, 7.54 ounces, a reversal of a trend that had seen birth weights climb steadily since the 1950s, according to the study. Babies were also born 2.5 days earlier on average in 2005 than in 1990, the study said.

The small decrease in weight—based on an analysis of nearly 37 million nonmultiple births from a national database—isn't likely to affect the health of the average baby in the study, according to researchers. But the data showed a 1% increase in the number of the lowest-weight babies and suggested the birth-weight decline didn't stop in 2005. . . .