Gestational diabetes develops when your body can’t make enough insulin to keep up with the extra demands of pregnancy. It affects roughly 6 to 10 percent of pregnancies, and the root cause is a combination of pregnancy-related hormone changes and your body’s ability (or inability) to compensate for them. Some women are more vulnerable than others based on genetics, weight, age, and ethnicity.
How Pregnancy Changes Your Insulin Response
Every pregnancy triggers a natural rise in insulin resistance, especially during the second and third trimesters. This is actually by design: your body becomes slightly less responsive to insulin so that more glucose stays in your bloodstream and crosses the placenta to fuel your growing baby.
The placenta drives this shift by releasing a cascade of hormones, including human placental lactogen, placental growth hormone, progesterone, estradiol, and prolactin. Cortisol, which also rises steadily throughout pregnancy, appears to be the strongest single contributor. In one study that compared changes in several pregnancy hormones against changes in insulin sensitivity, cortisol was the only one with a statistically significant correlation. Together, these hormones make your cells less receptive to insulin’s signal to absorb glucose from the blood.
In a healthy pregnancy, your pancreas compensates by ramping up insulin production. The insulin-producing beta cells expand in number, increase the amount of insulin they release per cell, and become more sensitive to glucose levels. When all four of these compensatory pathways (more beta cells, more insulin output, better glucose sensing, and stronger antioxidant defenses inside the cells) work properly, blood sugar stays in the normal range despite the rising resistance.
Gestational diabetes happens when that compensation falls short. In at-risk women, beta cells fail to keep pace with the growing insulin resistance. The result is insufficient insulin, rising blood sugar, and impaired glucose tolerance, the hallmark of gestational diabetes.
Who Is Most at Risk
Several factors make it harder for your pancreas to keep up with pregnancy’s insulin demands. The more of these that apply to you, the higher your overall risk.
- Higher body weight. A BMI above 25 (or above 23 for Asian Americans) is one of the strongest predictors. Excess body fat increases baseline insulin resistance before pregnancy hormones even enter the picture, meaning your beta cells start at a disadvantage.
- Low physical activity. Sedentary habits reduce your muscles’ ability to absorb glucose independently of insulin, adding to the burden on your pancreas.
- Age. Risk increases with maternal age, particularly after 35.
- Family history of diabetes. Having a parent or sibling with type 2 diabetes or gestational diabetes significantly raises your likelihood. Many of the same genes are involved in both conditions.
- Previous gestational diabetes. If you had it in an earlier pregnancy, the odds of recurrence are high.
- Polycystic ovary syndrome (PCOS). PCOS is closely linked to insulin resistance outside of pregnancy, which compounds the resistance that pregnancy adds.
- Previous large baby. Delivering a baby weighing 4,000 grams (about 8 pounds, 13 ounces) or more suggests your blood sugar may have run high during that pregnancy, even if gestational diabetes wasn’t formally diagnosed.
- Abnormal cholesterol or triglycerides. An HDL level below 35 mg/dL or triglycerides above 250 mg/dL are considered markers of metabolic risk.
Why Ethnicity Matters
Gestational diabetes rates vary dramatically across ethnic groups, and the differences are large enough that clinical guidelines list certain ethnicities as independent risk factors. In a large U.S. study, age-adjusted prevalence was lowest among non-Hispanic white women (4.2%) and Black women (4.4%). Rates were intermediate for Mexican American women (7.1%), Pacific Islanders (7.2%), and Chinese women (7.9%). The highest rates were among Southeast Asian women (8.8%), Filipinas (9.6%), and Asian Indian women (11.1%), nearly three times the rate seen in white women.
These disparities likely reflect a combination of genetic susceptibility, differences in body composition at lower BMI thresholds, dietary patterns, and access to healthcare. This is also why screening guidelines use a lower BMI cutoff (23 instead of 25) for Asian Americans.
The Genetic Component
Gestational diabetes doesn’t follow a simple inheritance pattern like some genetic conditions. Instead, it involves common gene variants that individually have small effects but collectively raise your susceptibility. Many of these genes overlap with those linked to type 2 diabetes, which explains why the two conditions run in the same families.
The genes involved fall into two broad categories: those that affect how well your pancreatic beta cells develop and function, and those that influence how sensitive your tissues are to insulin. Having several of these variants doesn’t guarantee you’ll develop gestational diabetes, but it means your beta cells may be less able to ramp up production when pregnancy demands it. Most affected women have at least one close family member with gestational diabetes or type 2 diabetes.
How Exercise Lowers Risk
Physical activity is one of the few modifiable factors with a strong, measurable effect. Staying active during pregnancy can lower your risk of gestational diabetes by roughly 40%, according to the American College of Sports Medicine. Exercise helps your muscles pull glucose out of the bloodstream more efficiently, reducing the workload on your pancreas. It also improves insulin sensitivity directly, partially counteracting the resistance driven by placental hormones. The benefit comes from regular moderate activity like brisk walking, swimming, or prenatal fitness classes rather than any single intense workout.
When It’s Detected
Gestational diabetes typically doesn’t cause noticeable symptoms, which is why routine screening is standard. The U.S. Preventive Services Task Force recommends screening all asymptomatic pregnant women at 24 to 28 weeks of gestation, the window when placental hormone levels are high enough for insulin resistance to become apparent. The test involves drinking a glucose solution and having your blood drawn afterward to see how your body handles the sugar load.
If you have significant risk factors, such as a BMI of 30 or higher combined with a family history of diabetes, previous gestational diabetes, PCOS, or a high-risk ethnicity, your provider may screen you earlier in pregnancy to catch pre-existing type 2 diabetes or early-onset gestational diabetes. Women who enter prenatal care after 28 weeks are screened as soon as possible.
The Connection to Type 2 Diabetes Later
Gestational diabetes resolves after delivery for most women once placental hormones leave the system. But the fact that your beta cells couldn’t keep up during pregnancy reveals an underlying vulnerability that doesn’t disappear. A previous diagnosis of gestational diabetes carries a lifetime risk of progressing to type 2 diabetes of up to 60%. Most of the progression happens in the first five years after the affected pregnancy, then the rate of new cases levels off considerably.
This is why postpartum glucose testing is important, and why the same protective strategies that lower gestational diabetes risk, particularly maintaining a healthy weight and staying physically active, remain relevant long after your baby is born.