Gestational Diabetes

Gestational diabetes, or diabetes diagnosed in pregnancy, affects 3% to 5% of pregnant women. Pregnancy is a state of increasing insulin resistance predominantly caused by placen-tally produced hormones, in particular human placental lacto-gen, which increases with placental mass and gestational age. Although most women can compensate, a small subset of pregnant women cannot. Early impairment of glucose metabolism may have no maternal signs or symptoms, but can have fetal effects that include macrosomia, fetal distress, and fetal demise.

Screening for gestational diabetes by a glucose challenge is recommended at 26 to 28 weeks of gestation. There is little evidence supporting earlier screening. The U.S. Preventive Services Task Force (USPSTF), however, concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for gestational diabetes mel-litus (GDM), either before or after 24 weeks' gestation and recommends that clinicians should discuss screening for GDM with their patients and make case-by-case decisions. Discussions should include information about the uncertainty of benefits and harms as well as the frequency of positive screening test results. Women who are obese, older than 25, have a family history of type 2 diabetes or gestational diabetes, or are members of certain ethnic groups, such as Hispanics, native Americans, Asians, and African Americans, are at increased risk for gestational diabetes.

The initial screening test is performed in a nonfasting state. The pregnant woman is asked to drink a mixture containing 50 g of glucose; 1 hour later a plasma glucose level is performed. If the result is 140 mg/dL or greater, the more definitive 100-g 3-hour glucose challenge is performed. The pregnant woman should have at least 3 days of adequate carbohydrate intake, fast the night before the test, and receive 100 g of glucose. Venous blood glucose is determined fasting and at 1, 2, and 3 hours after the glucose challenge. Two abnormal values make the diagnosis of gestational diabetes (Table 21-9). Different studies have various thresholds for making the diagnosis, and clinicians should review their institutional norms (Carpenter and Coustan, 1982) (Table 21-10). Women at high risk for gesta-tional diabetes, such as those with glucosuria, prior gestational diabetes, obesity, or strong family history, should be screened earlier in pregnancy. If negative, testing should be repeated in the latter half. The evidence supporting this practice is variable.

Initial therapies of gestational diabetes are diet and, if not contraindicated in the pregnancy, exercise in the form of walking, as well as support from diabetes educators and nutritionists and increased surveillance in prenatal care. The daily recommendation is 30 to 35 kcal/kg lean body weight. If fasting blood sugar cannot be maintained below 105 and

Table 21-9 Screening for Gestational Diabetes*


Abnormal Glucose Level (mg/dL)

50-g glucose, 1-hour challenge


100-g glucose, 3-hour challenge":



1 hour


2 hour


3 hour


From National Diabetes Data Group, 1979.

*Two abnormal values needed for diagnosis of gestational diabetes.

Table 21-10 Diagnosis of Gestational Diabetes Mellitus







1 hour



2 hour



3 hour



'National Diabetes Data Group, 1979.

fCarpenter MW, Coustan DR. Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 1982;144:768-773. OGTT, Oral glucose tolerance test.

2-hour postprandial blood sugars below 120 mg/dL, insulin therapy is begun. Hemoglobin A1c can be performed every 4 to 6 weeks but will not be elevated unless there is fasting hyper-glycemia. At least weekly evaluation of blood sugar is recommended because insulin resistance increases with advancing gestation. Ultrasonography to assess fetal size should be performed every 4 to 6 weeks. Women requiring insulin should have antenatal testing in the third trimester. Good blood sugar control is also important to decrease the incidence of metabolic newborn complications such as hypoglycemia, hypocal-cemia, polycythemia, and hyperbilirubinemia.

The family physician should remember that women who have had gestational diabetes have a 30% to 60% chance of developing type 2 diabetes mellitus in their lifetime (O'Sullivan, 1979). Postpartum and yearly glucose tolerance testing is recommended in these women. Weight loss and exercise have been shown to decrease their risk.


• The current evidence is insufficient to assess the balance of benefits and harms of screening for gestational diabetes mellitus (GDM), either before or after 24 weeks gestation.

• Screen for GDM using risk factor analysis and, if appropriate, use of an oral glucose tolerance test (OGTT) (SOR: C).

Data from American Diabetes Association (ADA), 2008; and U.S. Preventive Services Task Force (USPSTF), 2008.


Alpha-methyldopa (Aldomet), a central-acting alpha-adrenergic, false neurotransmitter, is the drug of choice for treatment of chronic hypertension in pregnancy (SOR: C).

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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