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The Glucose Test in Pregnancy: What to Expect, Normal Levels & How to Prepare
Between 24 and 28 weeks, almost every pregnant woman in the United States drinks a sweet liquid and has her blood drawn an hour later. That is the glucose challenge test, and the CDC times it there because gestational diabetes usually develops around the 24th week. A result of 140 mg/dL or below is normal; above that you are sent for a longer, fasting tolerance test, which is the one that actually diagnoses.
What the test is looking for
Pregnancy hormones make the body less able to use insulin. For most women the pancreas simply makes more. When it cannot keep up, blood sugar rises, and that is gestational diabetes. The CDC puts it at 5% to 9% of U.S. pregnancies each year, which is why the screen is offered to everyone rather than only to women with symptoms. There usually are no symptoms. The CDC notes that when they do appear they are mild, such as being thirstier than normal or urinating more often, and both are easy to write off as ordinary pregnancy.
Some women are tested earlier. NIDDK says that if you have risk factors, your doctor may test at the first visit after you become pregnant, then again at 24 to 28 weeks if the first result was normal. The CDC's risk-factor list includes gestational diabetes in a previous pregnancy, a previous baby weighing over 9 pounds, being overweight, a family history of type 2 diabetes, and polycystic ovary syndrome. Not sure which week you are in? Work out your estimated due date here first.
Step one: the one-hour glucose challenge
This is the easy one. MedlinePlus is explicit that you do not need to prepare or change your diet in any way, and NIDDK confirms no fasting is needed. You drink the glucose solution, wait an hour, and have blood drawn.
- Normal: 140 mg/dL (7.8 mmol/L) or below, per MedlinePlus.
- Above 140: NIDDK says you need further testing. This is a screening result, not a diagnosis.
- 200 or higher: NIDDK notes this may point to type 2 diabetes rather than gestational diabetes, and your provider will follow up accordingly.
A lot of women fail the one-hour and pass the three-hour. A high screen means "look closer," nothing more.
Step two: the oral glucose tolerance test
Two versions exist, and clinics choose one. Both require fasting. MedlinePlus says nothing to eat or drink other than sips of water for 8 to 14 hours beforehand, and, in the days before, to eat your normal food rather than cutting carbohydrates to game the result. The thresholds below are MedlinePlus's; a value at or above the number counts as abnormal.
| Protocol | Drink | Blood draws | Abnormal values (mg/dL) |
|---|---|---|---|
| Two-step (3-hour) | 100 g glucose | Fasting, then 1, 2 and 3 hours | Fasting ≥ 95 · 1 h ≥ 180 · 2 h ≥ 155 · 3 h ≥ 140 |
| One-step (2-hour) | 75 g glucose | Fasting, then 1 and 2 hours | Fasting ≥ 92 · 1 h ≥ 180 · 2 h ≥ 153 |
NIDDK's rule for reading the result: high blood glucose at any two or more of the draw times means gestational diabetes. Your clinic may apply the rule slightly differently for the one-step test, so ask which protocol it used before comparing numbers with a friend.
Practical bits nobody tells you: bring a snack for the moment the last tube is drawn, bring something to read, and plan the morning so you are not driving straight from a three-hour fast. If you tend to feel faint without breakfast, mention it when you book.
Home-monitoring targets after a diagnosis
If you are asked to check your own blood sugar, these are the targets NIDDK lists for most women with gestational diabetes. Your own care team may set different numbers, and theirs take priority.
| Timing | NIDDK target |
|---|---|
| Before meals, at bedtime, and overnight | 95 mg/dL or less |
| 1 hour after eating | 140 mg/dL or less |
| 2 hours after eating | 120 mg/dL or less |
Note these are treatment targets for daily readings, not the diagnostic cutoffs from the table above. Mixing the two is the single most common source of confusion in the Janeen support inbox.
Log fasting and post-meal readings with gentle daily reminders, switch between mg/dL and mmol/L, and export a clean PDF report to hand your provider at your next visit. Your data stays on your phone.
Download Janeen freeDiagnosed. Now what actually changes?
Less than you fear. The CDC's management list has four items: monitor your blood sugar, follow a healthy eating plan developed with your doctor or dietitian, be physically active, and take insulin if directed. That is the whole plan for most women.
On food, MedlinePlus's advice is unglamorous: moderate fat and protein, and go easy on foods with a lot of sugar such as soft drinks, fruit juices and pastries. Your dietitian will turn that into actual meals. On movement, NIDDK suggests aiming for 30 minutes of activity on 5 days of the week, even if you were not active before pregnancy; MedlinePlus names swimming, brisk walking and the elliptical as safe low-impact options.
If readings stay above target despite that, medicine comes next. NIDDK is direct about the part women worry about most: insulin will not harm your baby, and it is usually the first choice of diabetes medicine for gestational diabetes. Needing it says something about your placental hormones, not about your discipline.
Your provider may also add extra monitoring late in pregnancy. MedlinePlus describes a nonstress test, a belt on your abdomen that listens to the baby's heartbeat, as one common check.
Why it matters for the baby
MedlinePlus lists the reasons the numbers are worth chasing. A baby exposed to high sugar tends to grow large, which raises the chance of birth injury and of delivery by C-section. Newborns of mothers with gestational diabetes are also more likely to have periods of low blood sugar in the first days of life and may need monitoring in a neonatal unit. The CDC adds a longer view: these children are more likely to develop obesity or type 2 diabetes later. Well-controlled sugar shrinks every one of those risks.
⚠️ Call your provider promptly if
- Your readings are repeatedly outside the targets your care team gave you
- You are unsure how to respond to a high or low reading
- You have low-sugar symptoms (shakiness, sweating, dizziness), especially if you take insulin
- Your baby's movements decrease noticeably (see our kick counter guide)
After the birth
Blood sugar usually settles once the placenta is out, but the story does not end there. The CDC says about half of women with gestational diabetes go on to develop type 2 diabetes, and asks you to be tested 4 to 12 weeks after your baby is born, then every 1 to 3 years even if the first result is normal. NIDDK phrases it as no later than 12 weeks postpartum and every 3 years afterward. Put the first test in your calendar before you leave the hospital; it is the appointment most often forgotten. NIDDK also notes that breastfeeding helps you burn calories and that getting back to a healthy weight lowers your future risk.
FAQ
Do I need to fast for the glucose test?
Not for the one-hour glucose challenge: MedlinePlus says no preparation or diet change is needed. For the oral glucose tolerance test, MedlinePlus advises nothing but sips of water for 8 to 14 hours beforehand, and NIDDK says at least 8 hours.
What is a normal glucose test result in pregnancy?
For the one-hour challenge, MedlinePlus gives 140 mg/dL (7.8 mmol/L) or less as normal. On the three-hour tolerance test, values at or above 95 fasting, 180 at 1 hour, 155 at 2 hours, or 140 at 3 hours are abnormal, and NIDDK says two or more abnormal values mean gestational diabetes.
Will gestational diabetes go away after birth?
Blood sugar often returns to normal after delivery, but the CDC says about half of women with gestational diabetes later develop type 2 diabetes. Get tested 4 to 12 weeks after birth and then every 1 to 3 years.
Does gestational diabetes mean a C-section?
No. MedlinePlus notes it raises the chance of a C-section, mainly because the baby may grow large, but the diagnosis itself does not decide how you give birth. Your provider will weigh your readings and the baby's estimated size near term.
I felt sick and couldn't finish the drink. Now what?
Tell the clinic. It happens, especially if you are still dealing with morning sickness, and they will reschedule or switch you to the other protocol.
Bottom line
The glucose test is a routine check at 24 to 28 weeks, not a verdict on how you have eaten. A high one-hour screen means a longer test, and a diagnosis means a meal plan, some walking, a meter, and insulin only if the numbers call for it. Slot the test into your calendar with our prenatal appointment guide.
Official sources
- CDC: About Gestational Diabetes — accessed September 8, 2026.
- CDC: Diabetes During Pregnancy (postpartum testing) — accessed September 8, 2026.
- MedlinePlus: Glucose screening tests during pregnancy — accessed September 8, 2026.
- MedlinePlus: Gestational diabetes — accessed September 8, 2026.
- NIDDK: Tests and Diagnosis for Gestational Diabetes — accessed September 8, 2026.
- NIDDK: Managing and Treating Gestational Diabetes — accessed September 8, 2026.
- NIDDK: After Your Baby Is Born — accessed September 8, 2026.