Prenatal Screening for Gestational Diabetes

Gestational diabetes is a type of diabetes that starts during pregnancy. If you have diabetes, your body isn't able to use the sugar (glucose) in your blood as well as it should, so the level of sugar in your blood becomes higher than normal. Gestational diabetes affects about 4% of all pregnant women. It usually begins in the fifth or sixth month of pregnancy (between the 24th and 28th weeks). Most often, gestational diabetes goes away after the baby is born.

The standard method currently followed for screening of gestational diabetes mellitus (GDM) in expectant mothers is the one-hour glucose challenge test. However, there are some concerns that have surfaced regarding this test’s clinical efficacy. For example, test results may vary depending on the amount of time since a woman’s last meal. Also, the timing of the test has to be very precise with blood for the glucose test being drawn exactly one hour after ingesting the glucose. Also of concern are unpleasant side effects that the concentrated glucose can cause, often decreasing compliance with the test.

In a new study, researchers from California predicted that using the fasting plasma glucose as a screening test for diabetes early in gestation would offer advantages over the currently used postglucose challenge. The study involved more than 4,500 patients recruited from the Kaiser Permanente Bellflower Medical Center who were not known to have diabetes. All of the women were asked at their first prenatal visit to return for routine laboratory work and a venous plasma glucose test the next morning after a fast beginning no later than midnight. Upon testing, women whose blood sugar levels were 100 mg/dL to 125mg/dL were advised to have a glucose tolerance test immediately. Those women with a fasting plasma glucose concentration greater than or equal to 126mg/dL were asked to return for a second test. If the second test revealed similar numbers, those women were referred to care for diabetes. All women not identified as having diabetes were advised to have a two-hour GTT at their first visit after their 23rd gestational week.

However the study results showed that 302 women were identified as having gestational diabetes. The researchers say there was a false-positive rate of 57 percent to achieve a sensitivity of 80 percent. In other words, over half of all the patients who did not have gestational diabetes underwent a GTT to be able to identify 80 percent of those who did. These false-positive rates were significantly greater than those of other screening methods used to detect gestational diabetes. It is advised to have regular blood tests to check your blood sugar level. These tests will let your doctor know if your diet and exercise are keeping your blood sugar level normal. A normal blood sugar level is less than 105 mg per dL when you haven't eaten for a number of hours before the test (fasting) and less than 120 mg per dL 2 hours after a meal. If your blood sugar level is regularly higher than these levels, your doctor may ask you to begin taking a medicine called insulin to help lower it.

Researchers therefore concluded that, while detection of gestational diabetes early in pregnancy is a desirable goal, the implications of the current study show the fasting plasma glucose screening test given at the first prenatal visit is not an efficient screening test for gestational diabetes.

You may not need to have blood tests to check your blood sugar while you're in the hospital after your baby is born. However, it may be several weeks after your baby's birth before your gestational diabetes goes away. To make sure it has gone away, your doctor will ask you to have a special blood test one or two months after you have your baby.

Even if the gestational diabetes goes away after the baby's birth, it makes you have a higher risk for diabetes in your next pregnancy and later in life. That is why it is important that you continue to exercise, watch your weight and eat a healthy diet. If you do these things, you may not get diabetes when you're older.