Most people with gestational diabetes have no noticeable symptoms at all. That’s why the condition is detected through routine blood sugar testing, not by how you feel. Almost every pregnant person is screened between 24 and 28 weeks of pregnancy, and the diagnosis comes from the results of one or two lab tests.
Occasionally, gestational diabetes causes increased thirst or more frequent urination, but these overlap so heavily with normal pregnancy changes that they’re unreliable signals on their own. The screening tests are what actually tell you.
Why Most People Don’t Notice Symptoms
Gestational diabetes develops when your body can’t produce enough extra insulin to keep up with the hormonal shifts of pregnancy. Blood sugar rises gradually, and the levels involved are high enough to affect the pregnancy but rarely high enough to make you feel sick. Unlike type 1 or type 2 diabetes, where people sometimes experience dramatic thirst, blurred vision, or fatigue before diagnosis, gestational diabetes is nearly always silent.
This is precisely why universal screening exists. Your provider won’t wait for symptoms to appear, because they almost never do.
When and Why You’re Screened
Standard screening happens between 24 and 28 weeks of pregnancy. This is the window when pregnancy hormones most strongly interfere with insulin, making the condition detectable.
Some people are screened earlier, sometimes in the first trimester. Your provider may recommend early testing if you have one or more risk factors: a BMI of 25 or higher (23 or higher for Asian Americans), a first-degree relative with diabetes, a history of polycystic ovary syndrome, high blood pressure, or belonging to a higher-risk ethnic group (including African American, Latino, Native American, Asian American, or Pacific Islander). A previous pregnancy with gestational diabetes also puts you in the early-screening category. If early results come back normal, you’ll still be tested again at the standard 24-to-28-week window.
The First Test: Glucose Challenge
In the United States, most providers use a two-step approach. The first step is a glucose challenge test, which is a simple screening that doesn’t require fasting or any special preparation. You can eat and drink normally beforehand.
At your appointment, you’ll drink a sweet liquid containing 50 grams of sugar. It tastes like a very sweet soda or flat orange drink. You then wait one hour in the office or lab, during which you can’t eat or drink anything other than water. After the hour, a blood sample is drawn from your arm, and your blood sugar level is measured.
If your blood sugar comes back below the threshold your provider uses, you’re done. No further testing is needed. If it’s above the threshold, that doesn’t mean you have gestational diabetes. It means you need the longer, more definitive follow-up test. Roughly 15% to 20% of screened women end up needing that second test.
The Diagnostic Test: 3-Hour Glucose Tolerance
The follow-up is a three-hour oral glucose tolerance test, and it requires more preparation. You’ll need to fast for 8 to 14 hours beforehand, so it’s typically scheduled first thing in the morning.
When you arrive, your blood is drawn to get a fasting blood sugar reading. Then you drink a solution containing 100 grams of sugar, twice the amount from the screening test. Your blood is drawn again at one hour, two hours, and three hours after you finish the drink. Plan on being at the lab for at least three hours, and you won’t be able to eat during that time.
Four blood sugar values are measured, each with a specific threshold:
- Fasting: 95 mg/dL or higher
- One hour: 180 mg/dL or higher
- Two hours: 155 mg/dL or higher
- Three hours: 140 mg/dL or higher
If two or more of these four values come back above threshold, that confirms a gestational diabetes diagnosis. A single elevated value doesn’t meet the diagnostic criteria, though your provider may still recommend closer monitoring.
The One-Step Alternative
Some providers and health systems use a different approach recommended by the International Association of Diabetes and Pregnancy Study Groups. Instead of two separate tests, you take a single fasting test with 75 grams of sugar and blood draws at one and two hours. With this method, just one elevated value is enough for a diagnosis.
Because the bar is lower (one abnormal value instead of two), the one-step approach identifies about 18% to 20% of pregnant people as having gestational diabetes, roughly two to three times the rate found with the two-step method. A large randomized trial comparing the two approaches found no significant difference in short-term pregnancy outcomes, so which method your provider uses comes down to institutional preference. You don’t need to request one over the other.
What a Positive Result Means in Practice
A gestational diabetes diagnosis sounds alarming, but the condition is manageable and temporary. It means your blood sugar is high enough to potentially affect your baby’s growth and your delivery, so it needs to be controlled for the remainder of your pregnancy.
For most people, management starts with changes to what and when you eat. You’ll typically work with a dietitian or diabetes educator to learn how to balance carbohydrates across meals and snacks. You’ll also begin checking your blood sugar at home, usually by pricking your finger several times a day. Regular physical activity, like walking after meals, helps lower blood sugar as well.
Some people can keep their levels in range with diet and exercise alone. Others need insulin or medication to close the gap. Your provider will adjust the plan based on your home readings over the following weeks.
Gestational diabetes usually resolves after delivery. You’ll have a follow-up glucose test at 6 to 12 weeks postpartum to confirm your blood sugar has returned to normal. Having gestational diabetes does increase your risk of developing type 2 diabetes later in life, so staying active and maintaining a healthy weight after pregnancy offers real long-term protection.