Excessive weight gain during pregnancy, especially the first trimester, may increase a woman's risk of gestational diabetes, say U.S. researchers.

Their three-year study included 345 pregnant women with gestational diabetes and 800 pregnant women without gestational diabetes, which is defined as glucose intolerance that typically occurs during the second or third trimester of pregnancy.

After the researchers adjusted for a number of factors -- age at delivery, previous births, pre-pregnancy body-mass index and race/ethnicity -- they found that women who gained more weight during pregnancy than recommended by the U.S. Institute of Medicine were 50 percent more likely to develop gestational diabetes, compared to those whose weight gain was within or below the IOM recommendations.

The link between pregnancy weight gain and gestational diabetes was strongest among overweight and non-white women.

The study was published online Feb. 22 in the journal Obstetrics & Gynecology.

"Health-care providers should talk to their patients early in their pregnancy about the appropriate gestational weight gain, especially during the first trimester, and help women monitor their weight gain. Our research shows that weight gain in early pregnancy is a modifiable risk factor for gestational diabetes," lead author Monique Hedderson, a scientist at the Kaiser Permanente Division of Research in California, said in a Kaiser news release.

Gestational diabetes -- which causes complications in as many as 7 percent of pregnancies in the United States -- can lead to early delivery, cesarean section and type 2 diabetes in the mother. It also increases the child's risk of developing diabetes and obesity later in life.