The glucose test in pregnancy: what to expect and what results mean
A blood test after a sugary drink, used to check for gestational diabetes. It’s usually done at 24 to 28 weeks. In the US everyone is screened, and in the UK it depends on your risk.
Who has the test?
US: ACOG says all pregnant women are screened, earlier if you have risk factors, and otherwise at 24 to 28 weeks.
UK: the NHS offers the test if you have a risk factor, and earlier if you’ve had gestational diabetes before. Risk factors include:
- A BMI above 30
- A previous baby weighing 4.5 kg or more
- Gestational diabetes in a previous pregnancy
- A parent or sibling with diabetes
- South Asian, Black, African-Caribbean or Middle Eastern family origin
- Being over 40
- Weight-loss surgery
What happens on the day
UK: the oral glucose tolerance test (OGTT or GTT) takes about 2 hours. You have nothing to eat for 8 to 10 hours beforehand, then a blood test, a glucose drink, and another blood test after 2 hours.
US: many people have a 1-hour screening test first, sometimes called a glucose challenge test, then a longer test only if that’s high. Follow your clinic’s instructions, as fasting times differ. The drink is like a very sweet soda, and some people feel sick, sweaty or lightheaded afterwards.
US test results
| Test | Result that needs follow-up |
|---|---|
| 1-hour screen | Above 140 mg/dL (7.8 mmol/L) leads to a longer test |
| 2-hour test, 75 g drink | Fasting 92 mg/dL (5.1) or more, 1 hour 180 (10.0) or more, 2 hours 153 (8.5) or more |
| 3-hour test, 100 g drink | Fasting 95 mg/dL (5.3) or more, 1 hour 180 (10.0) or more, 2 hours 155 (8.6) or more, 3 hours 140 (7.8) or more |
Labs can use different cut-offs, and the NHS page we read doesn’t list numbers. Your care team will explain your result.
If you fail the 1-hour glucose test
Try not to panic. MedlinePlus says about 2 out of 3 women who have the longer test don’t have gestational diabetes. On that test, one high value may mean changes to your diet and a repeat test, and more than one means gestational diabetes.
If you have gestational diabetes
Most people have no symptoms. The NHS says you’ll be given a kit to test your blood sugar, with advice on diet and medicine if needed. It can mean a larger baby, and you should give birth before 41 weeks.
You should have a blood test 6 to 13 weeks after the birth, then every year.
Questions people ask
What if I fail the glucose test?
A high 1-hour result usually means a longer test, not a diagnosis. MedlinePlus says about 2 out of 3 women who have that test don’t have gestational diabetes.
Do I have to fast for the glucose test?
For the longer test, yes. The NHS says 8 to 10 hours and MedlinePlus says 8 to 14 hours, so follow your clinic’s instructions.
Does everyone have a glucose test?
In the US, ACOG says all pregnant women are screened. In the UK, the test is offered if you have a risk factor.
References
- NHS: Gestational diabetes
- ACOG: Gestational diabetes
- MedlinePlus: Glucose screening tests during pregnancy
Advice differs between countries, so follow your own care team’s plan. How we check this.
Second trimester, week by week
Second trimester Weeks 14–27
Growth, movement and senses. Often the most comfortable stretch for parents.
