Understanding your pregnancy glucose test result

Gestational diabetes is a serious medical condition that affects 6%–9% of pregnant women in the United States, according to the Centers for Disease Control and Prevention. When not adequately treated, gestational diabetes often has negative effects for both mom and baby. In an effort to diagnose gestational diabetes (which often has no symptoms), all pregnant women should be tested by using an oral glucose tolerance test (OGTT). The OGTT is generally administered around 28 weeks gestation (during the second trimester) as part of a routine prenatal visit. 

Pregnancy is naturally accompanied by increased insulin resistance to ensure that the fetus has ample nutrients especially as the pregnancy is in its third trimester. Gestational diabetes develops in those whose pancreatic function cannot overcome the natural insulin resistance

In this article, learn what the OGTT is, what it measures, and what your glucose test results mean. We’ll also give you tips on how to prepare for the test and what to do if your results are abnormal.

When is the glucose test done in pregnancy?

The pregnancy glucose test, formally known as the oral glucose tolerance test (OGTT), is a blood test that measures your body’s ability to break down sugar (glucose). This test diagnoses gestational diabetes, a type of diabetes (high blood sugar) that develops during pregnancy.

“The test is usually done around 24–28 weeks of pregnancy,” says Alex Juusela, MD, M.P.H., a maternal-fetal medicine fellow at Detroit Medical Center. “Earlier glucose screening is often performed when a patient has risk factors for undiagnosed pre-gestational diabetes and/or is at high risk for developing early gestational diabetes.”

Risk factors for gestational diabetes include: 

• Family history of diabetes
• Being overweight (BMI more than 25)
• Personal history of gestational diabetes in a prior pregnancy
• High blood pressure
• Polycystic ovary syndrome (PCOS)
• Elevated levels of glucose in the urine

“Because gestational diabetes often has no symptoms, it’s important that all women take a glucose test during pregnancy,” says Robert S. Wool, MD, an OB-GYN and medical director of Women’s Health Associates in Massachusetts. 

Pregnancy complications of gestational diabetes include: 

• High birth weight (greater than nine pounds)
• Higher risk of needing a C-section
• High blood pressure (preeclampsia)
• Low blood sugar (hypoglycemia) in the newborn
• Increased risk for stillbirth
• Increased risk of baby developing obesity or Type 2 diabetes later in life

How to prepare for glucose test

There are two different tests for glucose testing during pregnancy—one-step and two-step screening methods. Your healthcare provider will determine which testing method you use.

One-step testing

The one-step glucose screening method is a two-hour test that requires you to fast for at least eight hours beforehand—meaning only plain water should be consumed during this time. 

To start the test, your blood will be drawn to measure your fasting blood glucose level. You’ll then drink a sugary glucose solution that contains 75 g of sugar. You need to drink it within five minutes. Blood is taken one hour and two hours later. This evaluates how efficiently your body processes sugar. If either result from your two-hour test is outside of the standard range, your healthcare provider will diagnose you with gestational diabetes. 

Two-step testing

The two-step method is more commonly used. This consists of a one-hour glucose test, followed by a three-hour glucose test if blood sugar levels were outside of the expected range during the one-hour test. 

No preparation is needed and no fasting is required for the one-hour test. You’ll drink a sugary solution containing 50 g of glucose. A blood sample is taken one hour later. If these results are outside the standard range, you’ll need the three-hour glucose tolerance test.

For the second test, you’ll fast for at least eight hours beforehand. To start the test, your blood will be drawn to measure your fasting blood glucose level. You’ll then drink a 100 g glucose solution. Blood samples will be taken every hour for three hours to evaluate how your body processes sugar. If two or more of the four results from your three-hour test are outside of the standard range, you have gestational diabetes. 

Immediately following your glucose test, you can resume normal eating and drinking. Your healthcare provider will contact you with your results. 

Pregnancy glucose test results

You should receive the results of a prenatal glucose screening test within a few days, although you may receive them as early as a few hours later, depending on the lab and your healthcare provider. The best testing strategy and optimum glucose results to diagnose gestational diabetes to improve maternal and infant health is unclear. Many organizations have published recommendations which vary depending on which strategy your obstetrician adopts. Your pregnancy glucose test range will vary depending on the type of test you took.

One-step testing

During the one-step test, commonly known as the two-hour test, results are considered normal if they are below the following limits: 

• Fasting: 92 mg/dL
• One-hour glucose: 180 mg/dL
• Two-hour glucose: 153 mg/dL 

If your results meet or exceed one or more of these limits, your healthcare provider will diagnose you with gestational diabetes. 

Two-step testing

During step 1 of the two-step method, which is commonly known as the one-hour test or the glucose challenge test, results are considered normal if they are below the following limit:

• One-hour glucose: 130-140 mg/dL

If your results meet or exceed this limit during the one-hour test, you will need to proceed to step 2, which is commonly known as the three-hour test. During the three-hour test, results are considered normal if they are below the following National Diabetes Data Group limits:

• Fasting: 105 mg/dL
• One-hour glucose: 190 mg/dL 
• Two-hour glucose: 165 mg/dL 
• Three-hour glucose: 145 mg/dL 

If your results meet or exceed two or more of these limits during the three-hour test, you have gestational diabetes.

RELATED: Late-onset gestational diabetes

What do abnormal glucose test results mean?

The results of your glucose test show how well your body breaks down sugar. If your glucose test results are higher than the standard limit, your body is not processing sugar properly, a sign of gestational diabetes.

“Gestational diabetes usually occurs due to pregnancy-related hormonal changes. It’s important that patients not blame themselves or feel guilty for results of the hormonal changes of pregnancy, this is precisely why we screen all patients for gestational diabetes,” shares Dr. Juusela. 

“The good news is that for the most part, gestational diabetes can be successfully managed through diet, exercise and careful monitoring,” Dr. Wool says. “In cases where that is not enough, medications, such as insulin or metformin, can be used to help control blood sugar levels.” In other words, you can have a healthy pregnancy and a healthy baby with this condition.

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