Photo by Flickr user Martin Cathrae (CC BY-SA 2.0)

Between weeks 24 and 28, pregnant women are screened for gestational diabetes, a type of diabetes that develops for the first time in pregnancy. Those who screen positive typically return for a three-hour diagnostic test, which usually requires the pregnant woman finish a sugary drink and then undergo a series of blood draws over three hours. Women who have abnormal glucose readings are diagnosed with gestational diabetes. About 3 to 5 percent of pregnant women, or 135,000 per year in the U.S., are diagnosed.

A generation ago, doctors typically reassured women that the condition was temporary. But it is now clear that while blood sugar levels return to normal after the birth, gestational diabetes puts women at high risk of developing type 2 diabetes later in life.

A 2009 study published in The Lancet that pooled the results of 20 individual studies found that the lifetime risk of type 2 diabetes was about seven times higher in women who had gestational diabetes than those who did not. The U.S. Centers for Disease Control and Prevention estimates that anywhere between 15 and 50 percent of women who had gestational diabetes in pregnancy will develop type 2 diabetes.

Gestational diabetes can also cause more immediate problems, including babies that weigh more than 9 pounds at delivery. Big babies are more likely to dislocate a shoulder during birth and put women at risk of a Caesarean section.

Scientists do not know exactly how gestational diabetes leads to type 2 diabetes. Genetic studies provide some evidence that they have a common cause: Women who get gestational diabetes often carry the genes that predispose people to type 2 diabetes.

The risk factors for gestational diabetes are similar to those for type 2 diabetes and include:

• A previous pregnancy with gestational diabetes or a baby weighing more than 9 pounds
• Being overweight or obese
• Being older than 25
• Having a family history of diabetes
• Being African-American, Hispanic, American Indian, Alaska Native, Native Hawaiian, or Pacific Islander.

However, 40 to 60 percent of women who develop gestational diabetes have no known risk factors, which is why doctors in the U.S. typically require all pregnant women to be screened.

U.S. Centers for Disease Control and Prevention. Gestational Diabetes. http://www.cdc.gov/diabetes/pubs/pdf/gestationalDiabetes.pdf
Accessed November 21, 2011.

Bellamy, L et al. Type 2 diabetes mellitus after gestational diabetes: a systematic review and meta-analysis. The Lancet. 2009, 373(9677): 1773-9.