gestational diabetes

[Anonymous]

The prevalence of gestational diabetes varies worldwide and among racial and ethnic groups. Prevalence rates are higher in black, Latino, Native American, and Asian women than white women . The prevalence also varies with the testing methods and diagnostic criteria. Thus, the prevalence rate in the United States has varied from 1.4 to 14 percent in different studies .

RISK FACTORS AND SELECTION OF WOMEN FOR SCREENING — Clues that a pregnant woman may be at high risk for gestational diabetes are :

A family history of diabetes, especially in first degree relatives

Prepregnancy weight of 110 percent of ideal body weight or more or weight gain in early adulthood

Age greater than 25 years

A previous large baby (greater than 9 pounds [4.1 kg])

History of abnormal glucose tolerance

Member of an ethnic group with a higher than normal rate of type 2 diabetes

A previous unexplained perinatal loss or birth of a malformed child

The mother was large at birth (greater than 9 pounds [4.1 kg])

Polycystic ovary syndrome

Maternal low birth weight (<6 pounds [2.7 kg])




Selective screening — The American Diabetes Association (ADA) recommends that screening be limited to women with risk factors for gestational diabetes . Specifically, the ADA suggests that it is not cost-effective to screen women who are less than 25 years of age, have a normal body weight, no family history of diabetes, and are not at risk on the basis of race or ethnicity. The American College of Obstetricians uses similar criteria to define low-risk women .



In a comparison study, all women were screened with a 75 gm dose of glucose and a one-hour blood glucose cut-off value of less than 140 mg/dL (7.8 mmol/L) . The test not only was an excellent screening test but also a cost-effective diagnostic test to identify high-risk pregnancies.

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SCREENING TECHNIQUE AND DIAGNOSTIC CRITERIA — Screening is optimally performed at 24 to 28 weeks of gestation . However, it can be done as early as the first prenatal visit if there is a high degree of suspicion that the pregnant woman has undiagnosed type 2 diabetes .

Initially a 50-g oral glucose challenge is given and venous serum or plasma glucose is measured one hour later; a value 140 mg/dL (7.8 mmol/L) is considered abnormal. Women with an abnormal value are then given a 100-g, three-hour oral glucose tolerance test (GTT) . The sensitivity of the 50-g glucose test is improved it is performed in the fasting state or a lower serum glucose threshold (130 mg/dL) is used . At the 130 mg/dL threshold, the test is positive in 20 to 25 percent of pregnant women and detects 90 percent of gestational diabetics; at the 140 mg/dL threshold, 14 to 18 percent of tests will be positive and 80 percent of gestational diabetics will be detected . Either threshold may be used .

Other types of screening tests have been proposed and may be better tolerated, but are less sensitive . Capillary blood should not be used for screening tests unless the precision of the meter is known, it has been correlated with simultaneously drawn venous samples, and has met federal standards for laboratory testing.

Oral glucose tolerance test — Two different classification schemes of gestational diabetes based upon results of the three-hour GTT results have been proposed. According to the Fourth International Workshop-Conference on Gestational Diabetes, gestational diabetes is present if two or more of the following serum glucose values are exceeded:

Fasting serum glucose concentration >95 mg/dL (5.3 mmol/L)

One-hour serum glucose concentration >180 mg/dL (10 mmol/L)

Two-hour serum glucose concentration >155 mg/dL (8.6 mmol/L)

Three-hour serum glucose concentration >140 mg/dL (7.8 mmol/L)




Two-hour 75-g glucose tolerance test — A simplified 75 g glucose tolerance test may be more cost-effective than the three-hour test . The ADA and World Health Organization (WHO) have endorsed a two hour 75-g oral GTT for diagnosis of gestational diabetes, although they have different criteria for a positive test. Some clinicians use this test as a one step approach for both screening and diagnosis .

The ability of this test to predict adverse pregnancy outcome was assessed in the Brazilian Gestational Diabetes Study of 5000 women who had the test at 24 to 28 weeks of gestation . The incidence of gestational diabetes by ADA and WHO criteria was 2.4 and 7.2 percent, respectively. Each group's criteria predicted an increased risk for development of macrosomia, preeclampsia, or perinatal death , demonstrating the utility of this abbreviated test. However, very few of the women received dietary or drug treatment for hyperglycemia, therefore no conclusions can be drawn about the potential benefits of diagnosis and intervention in these women.

Other tests — According to the ADA, the diagnosis of gestational diabetes cannot be established without a confirmatory abnormal GTT. There are, however, other findings which can identify women at risk. As an example, a serum glucose concentration that is >140 mg/dL (7.8 mmol/L) after the 50-g glucose challenge is associated with a 25 to 30 percent risk of a macrosomic infant if no treatment is offered .

A fasting serum glucose concentration greater than 90 mg/dL (5 mmol/L) at 24 to 28 weeks of gestation, along with a hemoglobin A1c value above normal, is highly sensitive and specific predictor of subsequent infant macrosomia in the general obstetrical population . Hemoglobin values alone were not sufficiently sensitive to predict those women at risk of delivering a macrosomic infant. In one study, the sensitivity and specificity of a fasting serum glucose value of 86 mg/dL (4.8 mmol/L) or higher for detecting gestational diabetes were 81 percent and 76 percent, respectively .

These observations permit a simplified approach in some women. We found that the rate of macrosomia could be reduced from 18 to 7 percent using only a positive serum glucose screen (without performing an oral GTT) to refer women for dietary treatment, self blood glucose monitoring, and insulin therapy if blood glucose targets were not met on the prescribed diet . .

Summary — Universal screening for gestational diabetes should continue as the optimal strategy. There is no consensus regarding threshold values for the glucose challenge test. One analysis evaluated the cost per case of gestational diabetes diagnosed using various screening protocols . Universal screening using a threshold serum glucose concentration of 130 mg/dL (7.2 mmol/L) had 100 percent sensitivity, but 25 percent of women screened required a GTT and the cost per case diagnosed was $249 . Raising the serum glucose threshold value to 140 mg/dL (7.8 mmol/L) dropped the sensitivity to 90 percent with 15 percent of women screened requiring a GTT. In this protocol, the cost per case diagnosed was $222. Selective screening with a 140 mg/dL (7.8 mmol/L) threshold lowered the sensitivity to 85 percent at a cost of $192 per case diagnosed.


TYPE 1 DIABETES — Type 1 diabetes can present during pregnancy and may be mistaken for gestational diabetes. Clues to the presence of type 1 diabetes include:

Lean women

Diabetic ketoacidosis during pregnancy

Severe hyperglycemia during pregnancy requiring large doses of insulin

Postpartum hyperglycemia


Measurements of serum anti-insulin antibodies and anti-islet cell antibodies may be helpful for identifying type 1 diabetes in pregnant women . Women who have these antibodies during pregnancy should be advised to continue self blood glucose monitoring postpartum to document persistent hyperglycemia. If their blood glucose concentrations are normal during this period, fasting blood glucose should be measured every 6 to 12 months for the next 5 to 10 years.