Hot temps can cause low birth weights.

• Position: Pregnancy

Extreme hot or cold temperatures during pregnancy may increase the risk that infants born at term will be of low birth weight, according to a study of U.S. women by researchers at the National Institutes of Health, Bethesda, Md.

The authors found that exposure to atypically hot temperatures during the whole pregnancy, or during the third trimester, increased the risk for low birth weight. In addition, exposure to atypically cold temperature during the entire pregnancy, or just during the second and third trimesters, increased the risk for low birth weight. The odds for low term birth weight were highest when the entire pregnancy was exposed to extreme temperatures.

"Until we can learn more, it makes sense to reduce the amount of time that pregnant women are exposed to extreme hot or cold weather," says senior author Pauline Mendola, an epidemiologist in the Division of Intramural and Population Health Research at the National Institute of Child Health and Human Development.

Low birth weight refers to infants weighing less than 5.5 pounds when born. Infants may be of low birth weight because they are born prematurely, while others may be of low birth weight even though...