The glucose test in pregnancy
The glucose screening test checks for gestational diabetes — high blood sugar that starts or is found during pregnancy. According to MedlinePlus, most pregnant women have it between 24 and 28 weeks.
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Two ways to test
| Two-step testing | One-step testing | |
|---|---|---|
| Step 1 | Drink a glucose liquid; blood drawn 1 hour later. No fasting or diet change needed. | Fast 8 to 14 hours (sips of water only), then drink 75 g of glucose. |
| Step 2 | Only if step 1 is high: a 3-hour test after fasting 8 to 14 hours, drinking 100 g of glucose, with four blood draws. | Blood drawn before drinking and twice more, every 60 minutes. |
| Time to allow | About 1 hour (and at least 3 hours if step 2 is needed) | At least 2 hours |
From MedlinePlus. Your provider chooses the method.
Preparing and how it feels
MedlinePlus says to eat your normal food in the days before either test, and to ask your provider whether any of your medicines can affect the result. Most women have no side effects. The drink is like a very sweet soda; some women feel nauseated, sweaty, or lightheaded afterward. Serious side effects are very uncommon.
Results
For the two-step method, MedlinePlus says a normal screening result is most often a blood sugar of 140 mg/dL (7.8 mmol/L) or less one hour after the drink. A higher result leads to the 3-hour glucose tolerance test, which shows whether you have gestational diabetes — and most women (about 2 in 3) who take that follow-up test do not. Your provider will explain the thresholds they use.
Testing earlier, or not at all
The test may be done earlier if your urine shows high glucose at routine visits or you are at high risk for diabetes. MedlinePlus lists the conditions for being low-risk enough to skip it — including never having had high blood sugar, no first-degree relative with diabetes, and being younger than 25 with a normal weight. CDC’s gestational diabetes page explains risk factors and what happens after diagnosis.
Common questions
- Do I need to fast for the glucose test?
- Not for the 1-hour screening in two-step testing. You do need to fast 8 to 14 hours for the 3-hour test and for the one-step test.
- If I fail the 1-hour test, do I have gestational diabetes?
- Not necessarily. It means you need the 3-hour test; MedlinePlus says most women who take it do not have gestational diabetes.
Sources
- Glucose screening tests during pregnancy (opens in a new tab) — MedlinePlus, U.S. National Library of Medicine
- Gestational Diabetes (opens in a new tab) — Centers for Disease Control and Prevention (CDC)
Questions about this page
Tell us if something here is unclear or a source has changed. We cannot answer questions about your own pregnancy or care — please ask your OB, midwife, or care team. National Maternal Mental Health Hotline: call or text 1-833-TLC-MAMA (1-833-852-6262). Crisis: call or text 988.
We can’t answer questions about your own diagnosis, medication, or treatment — please ask your prescriber. We also can’t book appointments, check your insurance, or refer you to a clinic.
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Last reviewed against the public health sources linked on this page on .
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