Gestational diabetes develops when your body can’t make enough insulin to keep up with the extra demands of pregnancy. It affects 5% to 9% of U.S. pregnancies each year, and while certain risk factors make it more likely, it can happen to anyone who is pregnant.
What Happens Inside Your Body
During the first half of pregnancy, your body actually becomes more sensitive to insulin, the hormone that moves sugar from your blood into your cells. But as the placenta grows, it releases hormones that work against insulin. Two in particular, human placental lactogen and placental growth hormone, have strong blood-sugar-raising effects. The placenta also increases levels of estrogen, progesterone, and cortisol, all of which further reduce insulin’s effectiveness.
By the second half of pregnancy, your insulin sensitivity can drop by up to 60%. This is normal. Every pregnant person experiences some degree of insulin resistance because the goal, biologically, is to keep extra glucose available in the bloodstream for the growing baby. To compensate, your pancreas ramps up insulin production. The insulin-producing cells grow in both size and number to meet the demand.
Gestational diabetes happens when your pancreas can’t keep up. The compensatory increase in insulin falls short of what’s needed, and blood sugar stays elevated. This is why the condition typically shows up in the second or third trimester, when placental hormones are at their highest and the demand on your pancreas is greatest.
Who Is More Likely to Develop It
Some people have risk factors that make their pancreas less able to handle the insulin surge pregnancy requires. According to the CDC, your risk is higher if you:
- Had gestational diabetes in a previous pregnancy. Higher pre-pregnancy weight is a strong predictor of it happening again.
- Have overweight or obesity. This is one of the most significant modifiable risk factors.
- Are over 25 years old.
- Have a family history of type 2 diabetes.
- Have polycystic ovary syndrome (PCOS).
- Previously delivered a baby weighing over 9 pounds.
Ethnicity also plays a measurable role. A large study tracking U.S. births from 2011 to 2019 found that Asian/Pacific Islander women had the highest rates of gestational diabetes, nearly 103 per 1,000 live births compared to about 58 per 1,000 among non-Hispanic White women. Within Asian subgroups, Asian Indian women had the highest rate at 129 per 1,000 births. Hispanic/Latina women also had significantly higher rates. African American, American Indian, Alaska Native, and Native Hawaiian women face elevated risk as well. These differences reflect a combination of genetic susceptibility and systemic health factors, not personal choices.
The Role of Weight and Weight Gain
Carrying extra weight before pregnancy is one of the clearest risk factors because excess body fat already reduces insulin sensitivity before the placenta adds its own hormonal burden. But weight gained during pregnancy matters too. A study of over 1,100 women found that gaining more than about half a pound per week increased the risk of gestational diabetes by 43% to 74%, with the effect being even stronger in women who started pregnancy at a higher weight.
The CDC publishes weight gain guidelines based on your pre-pregnancy BMI. For a single pregnancy: if your BMI was in the normal range (18.5 to 24.9), the recommended gain is 25 to 35 pounds. If you started with a BMI of 25 to 29.9, the target drops to 15 to 25 pounds. For a BMI of 30 or higher, the recommendation is 11 to 20 pounds. Staying within these ranges doesn’t guarantee you’ll avoid gestational diabetes, but it meaningfully reduces the odds.
Diet and Activity Before and During Pregnancy
What you eat influences your risk in specific, measurable ways. Diets high in refined sugars, high-glycemic foods, and saturated fat are linked to higher rates of gestational diabetes. One striking finding: drinking five or more servings of sugar-sweetened cola per week was associated with a 22% increase in risk over a 10-year follow-up period. This doesn’t mean a single soda causes the condition, but a pattern of high sugar intake adds up.
Physical activity helps because working muscles pull glucose out of the blood independently of insulin, giving your overtaxed pancreas some relief. Exercise before and during pregnancy is one of the few interventions with consistent evidence for lowering gestational diabetes risk. Even moderate activity like brisk walking makes a difference.
How It Gets Diagnosed
Most pregnant people are screened between 24 and 28 weeks, the window when placental hormones are peaking and the condition becomes detectable. If you have known risk factors or your routine urine tests show elevated glucose earlier in pregnancy, your provider may screen sooner.
The standard screening starts with a one-hour glucose challenge. You drink a sugary solution, and your blood sugar is measured an hour later. A reading of 190 mg/dL or higher at the one-hour mark means gestational diabetes. If your result is elevated but below that cutoff, you’ll be asked to come back for a longer, three-hour test done while fasting. During that test, your blood sugar is checked at fasting, then at one, two, and three hours after drinking the glucose solution. If two or more of those readings come back above the expected thresholds (95 mg/dL fasting, 180 at one hour, 155 at two hours, 140 at three hours), you’ll receive a gestational diabetes diagnosis.
What It Means After Pregnancy
For most people, blood sugar returns to normal after delivery once the placenta is gone and its hormones clear the body. But gestational diabetes is a strong signal about your long-term metabolic health. Women who have had it face roughly 8 times the risk of developing type 2 diabetes compared to women who had normal blood sugar during pregnancy. A systematic review of 129 studies found that about a third of women with gestational diabetes developed type 2 diabetes within 15 years, with the risk climbing by about 12% for each additional year after delivery.
This doesn’t mean type 2 diabetes is inevitable. The same factors that reduce gestational diabetes risk, maintaining a healthy weight, staying physically active, and limiting refined sugars, also reduce the likelihood of progressing to type 2 diabetes after pregnancy. Postpartum glucose testing, typically done 6 to 12 weeks after delivery and then periodically, helps catch any changes early when they’re most manageable.