Gestational Diabetes: Testing, Targets, and Risks After Pregnancy

Your glucose test came back high, and your clinician says you have gestational diabetes. You may feel worried for your baby, or confused about what to eat now. You may also wonder whether it will go away after birth.

This guide explains how gestational diabetes is tested, the blood sugar targets clinicians use, how it is treated, and why follow-up after pregnancy matters.

What gestational diabetes is

Gestational diabetes (GDM) is high blood sugar that is first found during pregnancy. The placenta makes hormones that make the body resist insulin. Most people make extra insulin to keep up. When the body cannot keep up, blood sugar rises.[5]

It is common. Risk is higher with:[5]

• Higher body weight before pregnancy.
• Gestational diabetes in a past pregnancy.
• A parent or sibling with type 2 diabetes.
• Prediabetes or PCOS.
• Older age.
• South Asian, Black, Hispanic, Indigenous, or Asian ancestry.

What your doctor looks at

When testing happens

The USPSTF recommends screening for gestational diabetes at 24 weeks of pregnancy or later.[3] Diabetes Canada and the American Diabetes Association (ADA) also advise testing at 24 to 28 weeks.[1][2] People with risk factors may be tested early in pregnancy to look for diabetes that was present before.[1]

How the tests work

Canada and the US both accept more than one testing method.

The Diabetes Canada preferred approach is a two-step test:[2]

• Step 1: a 50 g glucose drink, with no fasting needed, and a blood test 1 hour later.
• A result of 11.1 mmol/L or higher at 1 hour diagnoses GDM.
• A result from 7.8 to 11.0 mmol/L leads to step 2.
• Step 2: a 75 g glucose tolerance test after fasting. GDM is diagnosed if one value is at or above: fasting 5.3, 1 hour 10.6, or 2 hours 9.0 mmol/L.

The ADA accepts two approaches:[1]

• A one-step 75 g fasting test. GDM is diagnosed if one value is at or above: fasting 92, 1 hour 180, or 2 hours 153 mg/dL (5.1, 10.0, and 8.5 mmol/L).
• A two-step approach with a 50 g screen, then a 100 g 3-hour test for those who screen positive.

Diabetes Canada also lists the one-step 75 g test with the lower cutoffs as an alternative.[2] The different cutoffs mean that the same result can be called GDM in one clinic and not in another.

Blood sugar targets

Once GDM is diagnosed, you check your glucose at home with a meter, usually before breakfast and after meals. Targets from Diabetes Canada and the ADA are very similar:[1][2]

• Fasting: below 5.3 mmol/L (95 mg/dL).
• 1 hour after a meal: below 7.8 mmol/L (140 mg/dL).
• 2 hours after a meal: below 6.7 mmol/L (120 mg/dL).

Your clinician may set different targets for you.

Why control matters

High blood sugar in pregnancy raises the chance of:[5]

• A large baby, which can make birth harder and raise the chance of a cesarean birth.
• Shoulder dystocia (the baby's shoulder gets stuck during birth).
• Preeclampsia (high blood pressure in pregnancy).
• Low blood sugar in the baby right after birth.

Good control lowers these risks.

Treatment

• Nutrition: a dietitian can help you spread carbohydrates across meals and snacks. The goal is steady glucose, not weight loss.
• Activity: regular walking and other safe exercise, especially after meals, can lower glucose.
• Medicine: if targets are not met, insulin is the preferred medicine in ADA guidance, because it does not cross the placenta in a meaningful way.[1] Metformin and glyburide cross the placenta. Diabetes Canada lists metformin as an option for some people.[2] Your clinician will explain the choice.
• Extra monitoring: you may have more ultrasounds to check the baby's growth.

After pregnancy: the part many people miss

GDM usually goes away after birth. The long-term risk does not.

• A large review found that people who had GDM had nearly 10 times the risk of type 2 diabetes compared with those who did not.[4]
• The ADA recommends a 75 g glucose tolerance test at 4 to 12 weeks after birth, and diabetes testing every 1 to 3 years for life.[1]
• Diabetes Canada recommends a 75 g glucose tolerance test between 6 weeks and 6 months after birth.[2]

Breastfeeding, healthy eating, activity, and weight management can lower the risk. Tell any future clinician that you had GDM.

Questions to ask your clinician

• Which test was used to diagnose me, and what were my numbers?
• What are my personal glucose targets, and when should I check?
• Can I see a dietitian or diabetes educator?
• What would make us start insulin or another medicine?
• How will my baby's growth be monitored?
• When should I have my glucose test after birth, and who will order it?

When to get care quickly

Go to the hospital or call your care team right away if you have:

• A severe headache, vision changes, or pain under the ribs on the right side.
• Sudden swelling of the face or hands.
• Your baby moving less than usual.
• Glucose readings that stay very high, or signs of low blood sugar that do not improve after treatment, if you take insulin.

Call 911 if you have chest pain, trouble breathing, a seizure, or fainting.

Bottom line

Gestational diabetes is common and treatable. Canada and the US use slightly different tests and cutoffs, but the treatment targets are almost the same. Most people manage it with food changes and activity, and some need insulin. The most important step after birth is follow-up testing, because the risk of type 2 diabetes stays high.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.