Glucose Tolerance Test

Screening for glucose tolerance in pregnancy

A glucose tolerance test is primarily used to screen patients for diabetes, so you might be wondering why you need a glucose screening during pregnancy. The truth is that pregnant women are at risk for developing a condition called gestational diabetes, which is a diabetic disorder that develops only after you become pregnant. The glucose tolerance test in pregnancy is usually administered early to assess your risk for gestational diabetes, regardless of whether or not you are experiencing any diabetic symptoms.

Pregnant women are routinely sent for a one-hour glucose screening at around 24 weeks, which gives only preliminary results. If the screening shows any cause for concern, your doctor will order a three-hour glucose tolerance test for a definitive diagnosis.

The Initial Glucose Screening

The glucose screening is a much simpler and faster test that the full tolerance test. There is no fasting or other preparation required. When you arrive for your appointment, you'll be given a sweet glucose solution to drink. An hour later, you'll have a blood sample drawn to measure how your body has processed the sugar you drank.

This screening is an important first step, but it does not diagnose gestational diabetes in and of itself. In fact, only one third of women who show abnormal results in the glucose screening actually have impaired glucose tolerance. If you get a positive result, your prenatal caregiver will order more a more rigorous glucose tolerance test to see if you are, in fact, developing gestational diabetes.

Preparing for Your Glucose Tolerance Test

In the days leading up to the test, simply eat, sleep and be active as normal. However, you cannot eat or drink anything for 8 to 14 hours before the test is administered, depending on the instructions of your caregiver. Tell your doctor about any and all medications and supplements you are taking, including prenatal vitamins, ahead of time. Your doctor will have to assess whether or not any drugs or supplements you're using may affect the results of your test. If he or she determines there is such a risk, you will be given personalized instructions on other preparations you'll need to make.

How the Oral Glucose Tolerance Test Works

First, your doctor will draw a blood sample. This is why you have to fast and avoid drinking before the test: your blood needs to be clean and free of all glucose so your doctor has a baseline from which to judge your tolerance.

Then, you will be given a more concentrated glucose solution to drink. Every hour for the next three hours, you'll have a blood sample drawn. These blood samples are compared to the baseline sample to check to see how your body reacts to glucose. Since the test takes three hours to complete, you should bring something to do between needles. Also keep in mind that you'll be extremely hungry by the time you leave, so bring some food for after the test.

If just one of your glucose measurements is abnormal, your doctor will likely continue to monitor your blood sugar throughout your pregnancy, and recommend some diet and lifestyle changes to help manage glucose. If two or more of the readings are abnormal, you'll be diagnosed with gestational diabetes, and your doctor will start a treatment plan right away.