The glucose screening test is typically done between 24 and 28 weeks of pregnancy. This is a routine part of prenatal care for most pregnancies, falling in the second trimester when hormonal changes are most likely to affect how your body processes sugar. If you have certain risk factors, your provider may screen you earlier.
Why 24 to 28 Weeks
Gestational diabetes develops when pregnancy hormones interfere with your body’s ability to use insulin effectively. These hormones ramp up during the second trimester, which is why the 24-to-28-week window is the standard screening period. Testing earlier than this in an average-risk pregnancy could miss the problem entirely, since blood sugar issues may not have surfaced yet. Testing much later leaves less time to manage the condition before delivery.
Who Gets Tested Earlier
If you have known risk factors, your provider may order the glucose test before 24 weeks, sometimes as early as your first prenatal visit. Obesity is one of the most common reasons for early screening. Other factors that may prompt earlier testing include a history of gestational diabetes in a previous pregnancy, a family history of type 2 diabetes, or a previous baby that weighed more than 9 pounds at birth. If early screening comes back normal, you’ll likely be tested again at the standard 24-to-28-week mark.
What Happens During the Test
Most providers in the U.S. use a two-step approach. The first step is a one-hour screening: you drink a sugary liquid containing glucose, and your blood is drawn one hour later. No fasting is required for this initial screen, so you can eat normally beforehand.
If your blood sugar comes back too high on that first test, it doesn’t automatically mean you have gestational diabetes. It means you need a second, more detailed test. This is the three-hour glucose tolerance test, which does require fasting overnight. Your blood is drawn before you drink a solution containing 100 grams of glucose, then drawn again at one hour, two hours, and three hours afterward. Your results across those four blood draws determine whether you have gestational diabetes.
Some providers use a one-step approach instead, which skips the initial screening and goes straight to a fasting test. In this version, you drink a solution with 75 grams of glucose and have your blood drawn three times: before drinking, at one hour, and at two hours.
What a Positive Result Means
A gestational diabetes diagnosis sounds alarming, but most people manage it effectively with lifestyle changes alone. The first line of treatment is dietary: focusing on foods high in fiber and nutrition while limiting refined carbohydrates like white bread, white rice, and sweets. Fruits, vegetables, whole grains, and lean protein become the foundation of meals.
You’ll also be asked to monitor your blood sugar regularly, typically four or more times a day. Most people check first thing in the morning and after each meal. Regular physical activity helps lower blood sugar too. Thirty minutes of moderate exercise on most days of the week is a common recommendation, with your provider’s guidance on what’s safe for your pregnancy.
If diet and exercise aren’t enough to keep blood sugar in a healthy range, insulin injections may be needed. Only a small number of people with gestational diabetes reach this point. Throughout the rest of your pregnancy, your provider will monitor your baby more closely with additional ultrasounds. If you don’t go into labor by your due date, or if there are concerns about the baby’s size, your provider may recommend inducing labor.
After Delivery
Gestational diabetes usually resolves once the baby is born. Your provider will check your blood sugar shortly after delivery and again at 6 to 12 weeks postpartum to confirm it has returned to a normal range. Even if it has, the condition signals a higher long-term risk for type 2 diabetes. You’ll need diabetes screening at least every three years going forward to catch any changes early.