Risk of Gestational Diabetes Rises from Weight Gain Between Pregnancies

A woman’s risk of developing gestational diabetes mellitus (GDM) increases when she gains weight between her first and second pregnancies, according to a study of more than 24,000 mothers in Norway.

“Our results emphasize the need for public health to expand its focus on healthy weight to include the interval between pregnancies, in order to prevent GDM,” study leader Linn Marie Sørbye, a public health researcher and PhD candidate at Norway’s University of Bergen (pictured), told MD Magazine.

GDM, a form of glucose intolerance that first occurs or is identified during pregnancy, can cause complications for both mothers and their babies. While being overweight is an important risk factor for the disorder, evidence suggests that weight gain between pregnancies independently increases the risk, according to the study.

To investigate that premise, Sørbye and her team reviewed data from Norway’s Medical Birth Registry for 2006 to 2014. The records included 24,198 mothers who’d had their first and second pregnancies during that time.

The researchers started by calculating the mothers’ weight gain, determining a woman’s prepregnant body mass index (BMI), or the ratio of her height to her weight. They subtracted the prepregnant BMI in the first pregnancy from the prepregnant BMI in the second to get the interpregnancy weight change. To find the gestational weight gain in the second pregnancy, prepregnant weight was subtracted from the weight at the end of the pregnancy.

All told, researchers found that the absolute risk of GDM in the second pregnancy was 18.1 per 1,000 pregnancies.

Weight gain from one pregnancy to the next proved to be an important indicator for GDM risk. Women who increased their weight by one unit of BMI or greater (for a woman who is 5.5 feet tall, gaining 6.6 pounds or more from the first to second pregnancy is defined as greater than 1 BMI unit) from the first to second pregnancy had a higher risk than those whose weight remained stable.

Mothers who gained between 1 and 2 BMI units had twice the risk of GDM, while those who gained 4 or more BMI units had a fivefold risk, the study found.

In one surprising result, the strongest risk associated with interpregnancy weight gain occurred among women with prepregnant BMI in the first pregnancy of less than 25, which is considered normal weight. The World Health Organization defines BMI of 25 through 29 as overweight and 30 and above as obese.

“The risk of GDM increased with increasing weight gain between pregnancies both in women with prepregnant BMI of less than 25 and for those with a BMI of 25 or greater in the first pregnancy,” Sørbye said.

In contrast, overweight women who reduced their weight from the first to second pregnancy saw a preventive effect for GDM, she added. “For women who are overweight (BMI≥25) at the start of their first pregnancy, a BMI decrease of more than 2 units may prevent GDM in their second pregnancy,’’ Sørbye told MD Magazine.

While the team noted that their results need to be replicated in other populations, they advised that weight change should be acknowledged as an independent factor for screening GDM in clinical guidelines. And Sørbye, who is also a midwife, has a strong suggestion for mothers hoping to reduce their risk of GDM, saying that “Women should be stable in weight from their first to second pregnancy.”

The study, “Gestational diabetes mellitus and interpregnancy weight change: A population-based cohort study” was originally published Aug. 1 in PLOS.