Gestational diabetes develops when your body can’t make enough insulin to overcome the natural insulin resistance that builds during pregnancy. Every pregnant person experiences some degree of this resistance, especially in the second half of pregnancy, but most can ramp up insulin production to compensate. When that compensation falls short, blood sugar stays elevated, and the result is gestational diabetes. It affects roughly 8 in every 100 pregnancies in the United States, a rate that has climbed steadily over the past decade.
What Happens Inside Your Body
The placenta is the driving force behind gestational diabetes. To keep the growing fetus supplied with a steady stream of glucose and amino acids, the placenta releases a cocktail of hormones that deliberately make your cells less responsive to insulin. The key players include human placental lactogen, progesterone, cortisol, estrogen, and placental growth hormone. Together, these hormones push more glucose into your bloodstream and keep it available for the baby.
Progesterone plays an especially strong role in the final trimester. It reduces how well insulin binds to your cells, slows glucose uptake in your muscles and fat tissue, and signals your liver to release more stored sugar. The net effect: your insulin sensitivity drops significantly over the course of pregnancy, and your body needs to produce up to 50% more insulin than it did before you were pregnant. Postmeal blood sugar peaks become higher and last longer.
For most people, the pancreas rises to the challenge. It churns out extra insulin, and blood sugar stays in a healthy range. Gestational diabetes happens when the pancreas can’t keep pace with the demand. The gap between what your body needs and what it can produce is what separates normal pregnancy metabolism from gestational diabetes.
When It Develops
Gestational diabetes usually appears around the 24th week of pregnancy. That timing lines up with the period when placental hormone production ramps up sharply and insulin resistance hits its peak. This is why routine screening is typically done between weeks 24 and 28. Before that point, the placenta hasn’t grown large enough to create the degree of resistance that overwhelms insulin production.
Some people with significant risk factors are screened earlier in pregnancy, sometimes at the first prenatal visit. If early screening comes back normal, a repeat test at 24 to 28 weeks is still standard because the metabolic landscape changes so much during the second and third trimesters.
Who Is Most at Risk
Certain factors make it harder for your pancreas to keep up with the rising insulin demand of pregnancy. The more of these you have, the higher your likelihood of developing gestational diabetes:
- Higher pre-pregnancy weight. Carrying extra body fat increases baseline insulin resistance before placental hormones even enter the picture, giving your pancreas less room to compensate.
- Physical inactivity. Muscle tissue is a major consumer of glucose. Less movement means less glucose uptake, which adds to the insulin burden.
- Prediabetes. If your blood sugar was already running on the high end before pregnancy, the additional resistance can tip you over the threshold.
- Previous gestational diabetes. Having it once significantly raises the chance it will return in a later pregnancy.
- Family history of diabetes. A parent or sibling with type 2 diabetes suggests a genetic tendency toward less efficient insulin production.
- Polycystic ovary syndrome (PCOS). PCOS is tied to insulin resistance independent of pregnancy. Research shows that people with PCOS have roughly 50 to 60% higher risk of gestational diabetes compared to those without it.
- Previous large baby. Delivering a baby weighing more than 9 pounds (4.1 kilograms) can be a sign that blood sugar was running high during that pregnancy, even if it went undiagnosed.
- Race and ethnicity. Black, Hispanic, American Indian, and Asian individuals face higher rates, likely driven by a combination of genetic, environmental, and systemic healthcare factors.
The Role of Weight and Weight Gain
Pre-pregnancy weight is one of the strongest modifiable risk factors. Higher body fat increases chronic low-grade inflammation and makes cells less sensitive to insulin before pregnancy begins. When placental hormones pile on additional resistance, the combined burden can exceed what the pancreas can handle.
How much weight you gain during pregnancy also matters. The CDC recommends different targets based on your starting BMI: 25 to 35 pounds for a normal-weight pregnancy, 15 to 25 pounds if you start overweight, and 11 to 20 pounds if you start with obesity. For twin pregnancies, the ranges are higher across every category. Gaining more than the recommended amount adds to insulin resistance and raises the risk of blood sugar problems in the third trimester.
Why It’s Becoming More Common
Gestational diabetes rates in the U.S. rose from about 58 per 1,000 live births in 2016 to roughly 79 per 1,000 in 2024, according to data published in JAMA Internal Medicine. That’s a jump of more than 35% in under a decade. Several overlapping trends help explain the increase: rising rates of obesity and prediabetes in people of childbearing age, more pregnancies at older ages, and broader screening that catches cases previously missed. The shift is not just better detection. The underlying metabolic health of the population entering pregnancy has changed.
What You Can Do to Lower Your Risk
You can’t control every risk factor (genetics, age, ethnicity), but the ones tied to metabolism are meaningfully modifiable. Staying physically active during pregnancy can lower your risk of gestational diabetes by about 40%, according to the American College of Sports Medicine. That doesn’t require intense exercise. Walking, swimming, and prenatal fitness classes all count. The key is consistent movement that helps your muscles pull glucose from the bloodstream.
Entering pregnancy at a healthy weight makes a substantial difference if that’s feasible. Even modest weight loss before conception can improve insulin sensitivity enough to give the pancreas more headroom once placental hormones kick in. During pregnancy, staying within the recommended weight gain range for your BMI category helps keep insulin resistance from compounding beyond what your body can manage.
Diet plays a direct role too. Meals built around fiber-rich carbohydrates, protein, and healthy fats produce slower, more gradual blood sugar rises than meals heavy in refined carbs and sugar. Spacing meals and snacks throughout the day prevents the sharp glucose spikes that stress an already-taxed insulin system. These aren’t just prevention strategies. They’re also the first line of management if you do develop gestational diabetes, which is why building these habits early in pregnancy offers a double benefit.
What Gestational Diabetes Is Not
Gestational diabetes is not type 1 or type 2 diabetes that happens to show up during pregnancy. It is a distinct condition caused by the metabolic demands of pregnancy itself. It typically resolves after delivery, once the placenta is gone and its hormones leave your system. That said, having gestational diabetes does signal that your pancreas was pushed to its limit, and it raises the long-term risk of developing type 2 diabetes later in life. About half of people who have gestational diabetes go on to develop type 2 within 5 to 10 years, which makes postpartum blood sugar monitoring important even after the pregnancy ends.