One of the most common complications of pregnancy is gestational diabetes mellitus (GDM). It is defined as glucose intolerance with first onset during pregnancy.1 In 2011, the incidence of GDM in the United States was between 2% and 10% of all pregnancies. Potential complications associated with GDM include macrosomia, pre-eclampsia, preterm birth, increased risk for cesarean section, neonatal hypoglycemia, shoulder dystocia, and polyhydramnios. Women with a history of gestational diabetes have a 35% to 60% likelihood of developing type 2 diabetes over the following 10 to 20 years.2
Q: When should screening for GDM occur?
According to the American Diabetes Association’s (ADA) 2012 Clinical Practice Recommendations, a pregnant woman should be screened for undiagnosed type 2 diabetes at her first prenatal visit if she has certain risk factors.3 These include, but are not limited to, family history of diabetes, overweight/obesity, sedentary lifestyle, elevated blood pressure and/or cholesterol, impaired fasting glucose or impaired glucose tolerance, or certain ethnic backgrounds (eg, Hispanic, Native American, and non-Hispanic black).4 In 2011, the ADA revised its recommendations for GDM screening and diagnosis to be in accordance with those from the International Association of Diabetes and Pregnancy Study Groups (IADPSG), an international consensus group with representatives from multiple obstetric and diabetes organizations, including ADA.
Q: How is GDM diagnosed?
Current recommendations stipulate that women with no previous history of diabetes or prediabetes undergo one-step testing: a 75-g glucose tolerance test (GTT) at 24 to 28 weeks’ gestation.5,6 For women with a prior history of GDM, screening is recommended earlier in the pregnancy. The GTT should be performed after an overnight fast of at least eight hours.3 An elevation of any one of the values above normal reference range is consistent with the diagnosis of GDM. (Previously, the diagnostic criteria required two abnormal values.) Multiple international studies using the new criteria have estimated an increased incidence of gestational diabetes in up to 18% of pregnancies.5,6
Some organizations have not endorsed the IADPSG/ADA diagnostic criteria at this time; as a result, many practitioners continue to use two-step testing for diagnosing GDM. To do the two-step testing, a 50-g glucose load is given, followed by a blood glucose reading one hour later. If the one-hour reading is within normal range, no further testing is warranted and the patient does not have gestational diabetes. If the test is abnormal, she must undergo a fasting three-hour GTT using a 100-g glucose load.
Q: What advice should a woman get once she’s diagnosed with GDM?
As soon as a woman is diagnosed with GDM, she should be referred for a gestational diabetes education class and nutrition counseling. Specifically, she should learn what it means for her to have GDM, implications for her and her baby, and the importance of eating a healthy diet (not the proverbial concept of “eating for two”), physical activity, self-monitoring blood glucose, and adherence to any prescribed medications.
Probably the most important aspect of education is nutrition counseling. It is known that smaller meals consumed more frequently throughout the day reduce spikes in blood glucose levels. One suggestion is to eat three small meals and three low-carbohydrate (15 g) snacks each day. Meals and snacks are generally established based on fixed carbohydrate amounts. A certified diabetes educator or registered dietitian (RD) can recommend healthy meal and snack ideas that are tasty, promote satiety, and minimize spikes in glucose levels.
Q: What are the current treatment options for GDM?
During the process of receiving GDM education, the patient should be prescribed a glucometer, along with specific glucose targets. Blood glucose should be checked multiple times a day, preferably fasting and postprandial measurements. Medical practices vary in their preferred glucose targets; some individuals require tighter control than others. The ADA suggests the following targets:
• Before a meal (preprandial):
95 mg/dL or less.
• One hour after a meal (postprandial): 140 mg/dL or less.
• Two hours after a meal (postprandial): 120 mg/dL or less. 7
If blood glucose levels remain within normal range, it is possible to control gestational diabetes with dietary modification and physical activity. If readings are consistently elevated, then the patient must be started on medication. There are currently no FDA-approved oral medications to treat gestational diabetes. Glyburide is commonly used, although it is not FDA approved for this indication. More studies to establish its safety are likely needed for FDA approval.8
If pharmaceutical treatment is warranted, insulin is the safest and most effective agent. It is the only medication that is FDA approved for treatment of GDM. Levemir (insulin detemir [rDNA origin] injection) gained FDA approval for use in pregnancy in 2012, so it has become more widespread than NPH for basal insulin usage.9