Babies born to women who are overweight or obese face a greater risk of major congenital malformations such as heart defects, according to a new study from the medical journal BMJ.

The risks, which increase progressively with weight status, range from 5 percent higher in women who are overweight (defined by the study as having a body mass index of 25 to 29), to 37 percent higher in women who are severely obese (defined as a BMI of 40 or over). Approximately half of women in the U.S. who become pregnant are overweight or obese.

The study also stressed that the risks of congenital heart defects, malformations of the nervous system, and limb defects also increased with the mother’s weight.

“We demonstrate increased risks of major malformations also in offspring of mothers with overweight and risks progressively increase with a mother’s overweight and obesity severity,” Martina Persson, a researcher in the clinical epidemiology unit at Karolinska Institutet in Stockholm who led the study, told CNN.

For Dr. Catherine Spong, the deputy director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development and a privately practicing OB-GYN, this study allows physicians to further explain and quantify for their patients the risks involved in pregnancy.

“Pregnancy itself is associated with risks just by being pregnant ”• you double your blood volume, you change your binding protein, you have a higher tendency to clotting,” Spong said. “If you have other medical conditions on top of that you enhance those risks.”

Spong referenced pre-eclampsia and gestational diabetes as conditions for which overweight and obese mothers have higher risk factors. 

She complimented this study, which she was not involved with, for its comprehensive duration and numbers. The study was performed in Sweden, where researchers tracked more than 1.2 million live births between 2001 and 2014 using the Swedish medical registry. Prenatal and delivery care is publicly funded in Sweden, and the “Swedish medical birth register includes information on close to 100% of all births in Sweden since 1973,” according to the study.

Persson told CNN that while the advice for pregnant women to be at a healthy weight may not be new, this quantification of risk helps “expand on previous knowledge.” 

For Spong, one salient point is the progressive relationship between weight and risk. 

“Were you even to just come down from being morbidly obese to obese you would reduce your risk to some degree,” she said. 

For Lucy Sullivan, the executive director of the nonprofit 1,000 Days, which stresses the importance of good nutrition in a child’s first 1,000 days from conception to his or her second birthday, this study affirms the importance of a healthy foundation for both mother and child.

“If we want healthy babies, we need to start with healthy mothers. And this means making sure that women enter pregnancy at a healthy weight, eat a nutritious diet during pregnancy and have access to good quality prenatal care,” Sullivan told HuffPost in an email.