Q: What are glucose screening and tolerance tests, and what can they tell me?

A: A glucose screening is a blood test that checks for gestational diabetes, a condition where your body becomes unable to properly process sugar from your diet, causing it to build up in your bloodstream. It's usually done early in the third trimester. While doctors recommend this test for all pregnant women (since about half of women who develop gestational diabetes have no known risk factors and may not have any symptoms either), having a glucose screening is especially important if you've had gestational diabetes during a previous pregnancy, have a family history of the condition, or are very overweight.

The screening involves drinking a syrupy sugar solution and then having your blood drawn an hour later to check your blood sugar levels. If they're too high (a sign that you may have developed gestational diabetes), your doctor will follow up with the more definitive glucose tolerance test. This involves fasting overnight and drinking a solution with even higher amounts of sugar. Your blood is then taken several times over a period of three hours to check for elevated blood sugar levels. Results from both tests are usually available immediately.

If your glucose tolerance test reveals that you have gestational diabetes, try not to worry. First, you're far from alone -- gestational diabetes is one of the most common pregnancy complications (about 3 to 5 percent of women develop it). In many cases, it can be controlled by diet, exercise, or insulin injections, if necessary. But if not properly managed, the excess sugar in your bloodstream can cause your baby to grow too big -- which can lead to your needing a c-section. Or it can cause other health problems for your baby, including jaundice, low blood calcium levels, or hypoglycemia (which means your baby's blood sugar levels drop too low to provide the energy they need for basic daily activities). That's why detecting gestational diabetes early is so important -- it allows you and your doctor to control the disease and do everything possible to protect your baby. The good news is that once your baby is delivered, your blood sugar levels usually get back to normal.

Copyright 2009

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