Among the most common complications of pregnancy is a high level of glucose in the blood, a condition known as gestational diabetes mellitus (GDM). Because it usually goes away after birth, GDM was not always seen as a serious concern, although the excess sugar often produces very large, hard-to-deliver newborns. “For a long time it was not regarded as a real disease,” says clinical epidemiologist Cuilin Zhang of the National University of Singapore. That has changed after multiple studies, including some by Zhang, linked the condition to a long-term risk of chronic diabetes for the mother and of obesity for the child.

This summer the first-ever national analysis of trends in gestational diabetes conducted by the Centers for Disease Control and Prevention brought alarming news. Between 2016 and 2020 the prevalence jumped 30 percent, affecting nearly 8 percent of U.S. pregnancies in 2020. Some increase was expected, says Elizabeth Gregory, a CDC health scientist and co-author of the report: “We know that risk factors, including overweight and obesity and older maternal age, have been increasing over time.” For those reasons, the condition has been rising globally. What was unexpected was a giant jump in a single year: GDM was up 13 percent in 2020, as opposed to about 5 percent in each of the previous four years.

The CDC report did not examine the reasons for the 2020 surge, but the COVID pandemic is an obvious culprit. “Decreased physical activity, weight gain and other lifestyle factors during lockdowns are known to impact gestational diabetes,” Gregory points out. An Italian study of 1,295 women, published earlier this year, supports this idea. It found that the incidence of GDM nearly tripled during lockdown periods—rising from 3.4 percent prelockdown to 9.3 percent. Pregnancy weight gain averaged 20.5 pounds during Italy's strict lockdowns versus 14.5 pounds prepandemic. A higher body mass index (BMI) was linked to greater risk.

Other contributing factors, Zhang says, could be a poorer diet—more snacking and less fresh produce—stress, inability to exercise and depression. Work by Zhang and her former colleagues at the National Institutes of Health showed that depression is associated with a higher risk of GDM, particularly in nonobese women.

The CDC analysis found that gestational diabetes rose in nonoverweight women as well as those with a high BMI. Those of non-Hispanic Asian origin had by far the highest incidence (14.9 percent); non-Hispanic Black women had the lowest (6.5 percent). Asian people in general tend to develop type 2 diabetes—a form in which the body does not use insulin effectively—at a lower BMI than do people of other ethnicities, and the same appears to be true with gestational diabetes. Learning why and what interventions might help was a key reason Zhang recently relocated to Singapore to head up her university's new Global Center for Asian Women's Health.

Women with gestational diabetes face about seven times the average risk of developing type 2 diabetes later in life, along with increased chances of cardiovascular disease. It is not clear whether GDM causes these ailments or if individuals who are vulnerable to GDM also have an underlying vulnerability to type 2 diabetes and heart disease. For the baby, there is a short-term danger of birth injury as a result of large size and a longer-term elevated risk of obesity and impaired glucose tolerance.

Zhang and others have shown that early intervention can reduce the likelihood of gestational diabetes. A 2016 study done in Finland, for example, found that a healthy diet and exercise regimen during pregnancy cut the incidence of GDM by 39 percent among participants who had a history of the ailment or who were obese. Evidence suggests that beginning such a regimen early in pregnancy—or better yet, before becoming pregnant—works best. Unfortunately, most pregnant patients are not tested for diabetes until the sixth or seventh month. Those with obesity or other risk factors are supposed to be screened much earlier, but that recommendation may not be widely followed by physicians, says obstetrician-gynecologist Veronica Gillispie-Bell of Ochsner Health Center–Kenner in New Orleans.

For low-income women who do not receive routine medical care, “pregnancy may be their first opportunity to find out if they have diabetes,” says Gillispie-Bell, who helps to lead Louisiana's efforts to reduce its high rate of maternal mortality. And the rise in GDM adds yet another element to an ongoing crisis in maternal and reproductive health.