Gestational diabetes is typically diagnosed between 24 and 28 weeks of pregnancy, when routine screening is part of standard prenatal care. If you have certain risk factors, your doctor may test you at your very first prenatal visit, potentially catching it in the first trimester.
The Standard Screening Window
For most pregnancies, screening happens during the late second trimester, between weeks 24 and 28. This timing isn’t arbitrary. Hormones from the placenta increasingly interfere with how your body uses insulin as pregnancy progresses, and the effect becomes measurable around this point. Testing earlier in a low-risk pregnancy would miss many cases that haven’t developed yet, while testing later would leave less time to manage blood sugar before delivery.
If your results come back normal at 24 to 28 weeks, you generally won’t need further glucose testing during the pregnancy unless new concerns arise, such as the baby measuring unusually large on ultrasound.
Who Gets Tested Earlier
Some people are screened at their first prenatal appointment, which could be as early as 8 to 12 weeks. The CDC identifies several factors that put you at higher risk:
- Previous gestational diabetes in an earlier pregnancy
- A prior baby weighing over 9 pounds at birth
- Being overweight before pregnancy
- Family history of type 2 diabetes
- Polycystic ovary syndrome (PCOS)
- Certain racial and ethnic backgrounds, including African American, Hispanic or Latino, American Indian, Alaska Native, Native Hawaiian, or Pacific Islander
When early testing comes back normal, you’ll still be screened again at 24 to 28 weeks, because the placental hormones that drive gestational diabetes ramp up as pregnancy advances. A clear result at 10 weeks doesn’t guarantee a clear result at 26.
Early screening also helps distinguish gestational diabetes from pre-existing type 2 diabetes that simply hadn’t been caught before pregnancy. A hemoglobin A1c of 6.5% or higher in the first trimester points toward type 2 diabetes rather than the gestational form, though A1c levels naturally dip in early pregnancy, so the cutoff isn’t perfect.
How the Tests Work
Most practices in the United States use a two-step approach. The first step is a glucose challenge test: you drink a sugary solution containing 50 grams of glucose, then have your blood drawn one hour later. You don’t need to fast beforehand. If your blood sugar reads between 130 and 140 mg/dL or higher (the exact cutoff varies by provider), you move on to the second step.
The second step is a longer, fasting test. After overnight fasting, you drink a solution with 100 grams of glucose and have your blood drawn four times: once fasting, then at one, two, and three hours. You’re diagnosed with gestational diabetes if at least two of those four readings exceed specific thresholds. The most commonly used cutoffs are a fasting level of 95 mg/dL, 180 mg/dL at one hour, 155 mg/dL at two hours, and 140 mg/dL at three hours.
A less common alternative is the one-step approach, which skips the initial challenge and goes straight to a fasting test with 75 grams of glucose. Under this method, only one elevated value is needed for a diagnosis: a fasting level of 92 mg/dL or higher, 180 mg/dL or higher at one hour, or 153 mg/dL or higher at two hours. Because the threshold for diagnosis is lower and only one abnormal value is required, the one-step method identifies more cases.
What Happens After Diagnosis
Once gestational diabetes is confirmed, you’ll start monitoring your blood sugar regularly, usually multiple times a day. The target goals are a fasting blood sugar under 95 mg/dL, under 140 mg/dL one hour after meals, or under 120 mg/dL two hours after meals. For many people, dietary changes and physical activity are enough to stay within these ranges. When blood sugar remains stubbornly high despite those adjustments, insulin or other medications become part of the plan.
Your care team will also monitor fetal growth more closely. High maternal blood sugar causes extra glucose to cross the placenta, which can lead to the baby growing larger than expected. Babies over 9 pounds face higher risks of birth injuries, shoulder complications during delivery, and cesarean delivery. In some cases, early delivery is recommended if the baby is measuring very large.
Why Gestational Diabetes Often Has No Symptoms
One reason screening is built into routine prenatal care is that gestational diabetes rarely produces noticeable symptoms. You won’t necessarily feel different. Occasionally, excessive thirst or frequent urination might stand out, but these overlap so heavily with normal pregnancy that they’re unreliable signals. The condition is almost always caught through lab work rather than symptoms, which is why skipping or delaying the glucose test can mean missing the diagnosis entirely during the window when management makes the biggest difference.
Postpartum Testing
Gestational diabetes usually resolves after delivery, but it signals a significantly higher lifetime risk of developing type 2 diabetes. Current guidelines recommend a 75-gram oral glucose tolerance test between 4 and 12 weeks after delivery to check whether blood sugar levels have returned to normal, shifted into prediabetes territory, or progressed to type 2 diabetes. This postpartum test uses standard, non-pregnancy diagnostic criteria, so the thresholds differ from the ones used during pregnancy.
Even if your postpartum results are normal, ongoing screening every one to three years is generally recommended, since the elevated risk of type 2 diabetes persists for years after a pregnancy affected by gestational diabetes.