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Pregnancy & Prenatal Testing

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Second Trimester: Blood Glucose

During pregnancy, at least 3% of women with no prior history of diabetes will develop gestational diabetes (increased glucose levels). Although it can occur at any time, most cases will develop during the later part of the pregnancy. If increased blood sugar levels in the pregnant woman are uncontrolled, they can cause the fetus to increase in size and weight. They can also cause the baby to be born with very low glucose levels and to have breathing difficulties.

Most women are checked for gestational diabetes between 24 and 28 weeks of pregnancy. Women at high risk or who have high sugar in two routine urine tests (see urine screen for sugar and/or protein) may be tested sooner.

In 2013, the U.S. Preventive Services Task Force released new guidelines recommending that all pregnant women be screened for gestational diabetes after 24 weeks of pregnancy. In contrast, the American Academy of Family Physicians has stated that the evidence is insufficient to recommend for or against routine screening of asymptomatic pregnant women.

The American College of Obstetricians and Gynecologists recommends universal screening for gestational diabetes among pregnant women using patient history, risk factors, or laboratory testing (such as with a glucose challenge test, GCT) even though women at low risk may not benefit from the testing. The American Diabetes Association also recommends universal screening and in 2011 adopted new guidelines that recommend changes in gestational diabetes testing. The guidelines advise that all pregnant women be tested using a 2-hour oral glucose tolerance test. (See the article on Glucose for more on this.) The changes were made to help identify babies at higher risk of adverse outcomes, even though the mothers have glucose levels that are increased but still considered to be within the normal limits of older guidelines.

At this point, it is unclear if practice will change as result of these revised recommendations. However, pregnant women should discuss the pros and cons of screening with their obstetrician. Those at higher risk for gestational diabetes may benefit more from the testing. Risk factors include older age, ethnicity with higher rate of diabetes, obesity, family history of diabetes, and personal history of gestational diabetes with a previous pregnancy.  

For those with gestational diabetes, diet control and/or insulin injections throughout the rest of the pregnancy may be required to bring glucose levels down to normal levels. In most cases, gestational diabetes will go away after delivery, but women who have gestational diabetes will be at an increased risk of having it again with subsequent pregnancies and of developing type 2 diabetes in the future.

National Diabetes Information Clearinghouse: What I Need to Know about Gestational Diabetes

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