Expectant mothers who are fit before pregnancy are at a lower risk of developing gestational diabetes, a study suggests.

Gestational diabetes is a condition in which women develop diabetes during the last half of pregnancy.

Women with gestational diabetes are more likely to develop Type 2 diabetes after giving birth.

“Women are very careful during pregnancy with what they eat and the exercise they get. But the study shows women should engage in these healthy behaviours before they get pregnant as well,” said co-author Kara Whitaker, an assistant professor from the University of Iowa.

For the study, published in the journal Medicine and Science in Sports and Exercise, the team analysed data from 1333 women over a 25-year period (1985 to 2011) who enrolled in a National Heart, Lung and Blood Institute study titled Coronary Artery Risk Development in Young Adults.

The women completed seven study visits after first being enrolled, reporting whether they had become pregnant or given birth and whether they developed gestational diabetes.

The researchers also performed a fitness exam during the first study visit by testing whether the women could walk for two-minute intervals on a treadmill at increasing speeds and on steepening inclines.

Over the study, 164 women developed gestational diabetes.

Using that information, the research team determined that pre-pregnant women with high levels of fitness had a 21% lower risk of developing gestational diabetes than did those with lower fitness levels.

“People interested in becoming more fit can do so by engaging in at least 150 minutes of moderate to vigorous physical activity per week - 30 minutes per day, five days per week,” Whitaker said.