Doctors should advise overweight moms considering another pregnancy to take off extra weight first because they are at greater risk of having big babies, a new Saint Louis University study finds.

Researchers found that moms who don't lose the weight they gained during the first pregnancy and continue to gain after their first child is born are at risk of having bigger babies than mothers who do not gain weight between pregnancies. A patient's prepregnancy weight remained the strongest predictor for the birth of a large infant in the next pregnancy.

"Our advice to moms is to take off the weight they gained during one pregnancy and not to gain weight between pregnancies," said Robert Blaskiewicz, M.D., professor of obstetrics, gynecology and women's health at Saint Louis University.

Large babies can be more difficult and take longer to deliver than normal weight babies because they are too big to fit easily through the birth canal. Large birth weight also might lead to a cesarean delivery.

"The ideal is to have their weight as close to normal as possible. Weight gain between pregnancies doubles the risk of having a 'large for gestational age' baby."

Dr. Blaskiewicz presented the research, which was conducted in conjunction with the Saint Louis University School of Public Health, at the May meeting of the American College of Obstetricians and Gynecologists.

Dr. Blaskiewicz compared 38,086 women who were of normal weight at their first and second pregnancies with 10,585 women who were of normal weight for their first pregnancy but overweight for their second.

A baby who is "large for gestational age" typically weighs about eight pounds, 13 ounces. Most babies weight about seven pounds.