News Review From Harvard Medical School -- 1-Step Pregnancy Diabetes Test Not Endorsed
Changing the test used for pregnancy diabetes could diagnose more women. However, an expert panel is urging caution. About 5% of pregnant U.S. women are diagnosed with gestational (pregnancy) diabetes. This problem usually goes away after the birth. However, it can cause problems, such as an increase in larger babies and cesarean section deliveries. These mothers also are more likely to develop type 2 diabetes later in life. Diagnosis allows for treatment with diet, exercise and sometimes medicines. The most common test used in the United States is a two-step process. But the American Diabetes Association supports a one-step test. This test also lowers the blood sugar level required for diagnosis. The National Institutes of Health gathered a group of experts this week to look at the issue. They supported keeping the two-step test for now. They said the one-step test could diagnose gestational diabetes in 15% to 20% of pregnant women. That would drive up health care costs. More research is needed to show whether it also would benefit the babies or the mothers, the panel said. The Associated Press wrote about the report March 7.
By Mary Pickett, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Hormones that are produced during pregnancy can make blood sugar climb to higher-than-expected levels. This is diabetes in pregnancy, also known as gestational diabetes. This condition needs treatment. Otherwise, it can lead to problems during delivery. Potential problems include:
- Difficult delivery because of a large baby
- Shoulder dislocation for the baby during childbirth
- Higher chance of a need for cesarean section (C-section)
- Higher risk of a dangerous problem called preeclampsia
- Higher risk of stillbirth
It is important for all pregnant women to have testing so that gestational diabetes can be diagnosed and treated.
But what should be our threshold for diagnosing diabetes in pregnancy? All pregnant women have a shift in their metabolism. Two hormones that are produced in a normal pregnancy partially block the effects of insulin. For some women, this shift brings out diabetes that needs treatment.
Some other women are "borderline." They might have high blood sugar levels that look like diabetes if they eat an unusually large amount of sugar. But if they keep to a more usual diet they might never have high blood sugar. Should we diagnose even borderline women with gestational diabetes?
Expert groups are debating this right now. They are considering which test is best for finding diabetes in pregnancy. Current tests look at the way sugar levels in the blood change after a woman drinks a "load" of glucose. But how big a load?
- The 2-step test: Most women will pass a test using a 50-gram sugar load. That's just a bit higher than the amount in a typical soda. Women who have even a slight increase in their blood sugar on this test get a second test with a much higher sugar load. The second test can confirm diabetes.
- The 1-step test: This test uses a 75-gram sugar load. It's what you might get if you shotgunned 2 cans of soda. Women are asked to drink this extremely sweet drink in a quick 5 minutes. This test is harder to pass. Almost 1 out of 5 women will show abnormally high blood sugar afterward. When this test is used, the number of women who are diagnosed with gestational diabetes triples, compared with the 2-step test.
The American Diabetes Association and the World Health Organization say that either test is fine to use. However, they prefer the simplicity of the one-step test.
But a panel assembled by the National Institutes of Health (NIH) says it's not clear we have enough evidence to favor the one-step test. This test may diagnose too many women, including those in the "borderline" group. Diagnosing too many women generates extra health costs and anxiety. It also may expose a few women to tests and treatments they don't need.
It is not clear that much is gained by diagnosing and treating "borderline" women. A benefit is likely, but not yet proven.
I have been pregnant several times, and my doctors did the one-step test on me. But I agree with the NIH panel that there is reason to be skeptical about whether the one-step test is better. That test does not reflect the way most women eat. I worry that it diagnoses too many women with diabetes.
When I was pregnant, I worried about many things. It eased my mind to be told, "You have a normal pregnancy." It is fair for women with borderline gestational diabetes to be reassured that they have normal pregnancies, too.
What Changes Can I Make Now?
All pregnant women should be tested for gestational diabetes. All women also should be counseled about healthy diet, weight management and exercise habits. These things can help to limit the chance that gestational diabetes will develop.
Tests for gestational diabetes are usually done between 24 and 28 weeks of pregnancy. Tests should be done sooner for women who:
- Are overweight
- Have a family history of diabetes
- Have possible diabetes symptoms, such as frequent urination or repeated yeast infections
You can have either the 50-gram or the 75-gram test. They both work. The 50-gram glucose challenge is the first part of the 2-step test. It diagnoses fewer women with diabetes.
If you are diagnosed with gestational diabetes, it is important to monitor your blood sugar closely during pregnancy. Some women can be treated with good attention to diet, exercise and weight control. Others will need to use an oral medicine such as metformin (Glucophage) to control blood sugar. Some women will need to use insulin injections.
Diabetes that appears in pregnancy usually goes away after pregnancy. But if you have this condition, there is a 40% chance that you will develop type 2 diabetes later in life.
What Can I Expect Looking to the Future?
Several groups make recommendations about testing in pregnancy. For now, they are giving different advice. It will be very helpful if all of the experts can agree about which method of testing is the most sensible one.