Gestational diabetes is a form of diabetes that appears in pregnant women. It can occur in women with no previous sign of diabetes and often disappears after a woman gives birth. It begins when a woman's body is not able to make and use all the insulin it needs for pregnancy. Without enough insulin, glucose cannot leave the blood and be changed to energy. As high levels of glucose build up in the blood, hyperglycemia develops.

Gestational diabetes can cause difficulties for both mom and baby. Mothers who develop it are at risk for high blood pressure and preeclampsia and can go into labor early. It can also mean babies gain excessive weight while in the uterus, leading them to become stuck in the birth canal, experience injury during birth or require a C-section. Respiratory stress syndrome and low blood sugar after birth are two other threats to the baby that can be brought on by gestational diabetes.

Over 35 percent of the women studied gained more than one BMI (body mass index) unit from the beginning of their first pregnancy to the beginning of their second pregnancy.

Women are routinely screened for gestational diabetes around the 24th week of their pregnancies. A family history of type 2 diabetes, being over the age of 25 and being overweight are considered risk factors for the disease. Now research suggests that the amount of weight a mother gains between pregnancies may also be a risk factor.

Using data from the Medical Birth Registry of Norway, information on nearly 25,000 women was used to study the effect of weight gain between pregnancies on the risk of developing gestational diabetes. Over 35 percent of the women studied gained more than one BMI (body mass index) unit from the beginning of their first pregnancy to the beginning of their second pregnancy.

Compared to women whose weight remained stable between pregnancies, those who gained weight had a higher risk of developing gestational diabetes during their second pregnancy. The risk doubled for women who gained between one and two BMI units between pregnancies. Women whose weight increased by two to four BMI units had over two and a half times the risk of developing gestational diabetes, and the chance was five-fold for women who gained four BMI units or more.

The risk was greatest in women who were not overweight (BMI less than 25) at the beginning of their first pregnancy. And overweight women who reduced their BMI by two BMI units between pregnancies were less likely to develop the disease.

While the thought of eating for two may sound fun, women need to understand the importance of slow and steady weight gain during pregnancy, losing the extra “baby weight” after delivery, and maintaining a healthy weight between pregnancies to reduce their chance of developing gestational diabetes during the next pregnancy.

Physician guidelines for monitoring a woman's condition during pregnancy should include calculating her weight change between pregnancies, according to the authors of the study, in addition to a routine glucose tolerance test for women whose weight increases by more than one BMI unit during pregnancy.

The study is published in PLOS Medicine.