U.S. newborns are weighing less, study finds

Average birth weights have dropped slightly from 1990 to 2005. Researchers are unclear why.
By Jeannine Stein
January 22, 2010

Birth weights in the United States are on the decline, a study has found. The report, released Thursday, found a small but significant decrease in average birth weights from 1990 to 2005, for reasons that scientists say are unclear.

The numbers, published in the February issue of the journal Obstetrics & Gynecology, mark a shift from earlier reports that noted a rise in birth weights in the latter part of the 20th century.

They also seem to go against conventional wisdom, experts said. In recent years, women have gotten larger, are smoking less and are older when they have children, all factors that contribute to higher birth weight in offspring. the rest