Diabetes Monitor - gestational diabetes guidelines

Detection and Diagnosis

Risk assessment for gestational diabetes mellitus should be undertaken at the first prenatal visit. Women with clinical characteristics consistent with a high risk of gestational diabetes mellitus (marked obesity, personal history of gestational diabetes mellitus, glycosuria, or a strong family history of diabetes) should undergo glucose testing (see below) as soon as feasible. If they are found not to have gestational diabetes mellitus at that initial screening, they should be retested between 24 and 28 weeks of gestation. Women of average risk should have testing undertaken at 24 to 28 weeks of gestation. Low-risk status requires no glucose testing, but this category is limited to those women meeting all of the following characteristics:

Age <25 years
Weight normal before pregnancy
Member of an ethnic group with a low prevalence of gestational diabetes mellitus
No known diabetes in first-degree relatives
No history of abnormal glucose tolerance
No history of poor obstetric outcome

A fasting plasma glucose level >126 mg/dL (7.0 mmol/L) or a casual plasma glucose >200 mg/dL (11.1 mmol/L) meets the threshold for the diagnosis of diabetes, if confirmed on a subsequent day, and precludes the need for any glucose challenge. In the absence of this degree of hyperglycemia, evaluation for gestational diabetes mellitus in women with average or high-risk characteristics should follow one of two approaches:

One-step approach: Perform a diagnostic oral glucose tolerance test (OGTT) without prior plasma or serum glucose screening. The one-step approach may be cost-effective in high-risk patients or populations (e.g., some Native-American groups).

Two-step approach: Perform an initial screening by measuring the plasma or serum glucose concentration 1 hour after a 50-g oral glucose load (glucose challenge test [GCT]) and perform a diagnostic oral glucose tolerance test on that subset of women exceeding the glucose threshold value on the glucose challenge test. When the two-step approach is employed, a glucose threshold value >140 mg/dL (7.8 mmol/L) identifies approximately 80% of women with gestational diabetes mellitus, and the yield is further increased to 90% by using a cutoff of >130 mg/dL (7.2 mmol/L).

With either approach, the diagnosis of gestational diabetes mellitus is based on an oral glucose tolerance test. Diagnostic criteria for the 100-g oral glucose tolerance test are shown in Table 1, below. Alternatively, the diagnosis can be made using a 75-g glucose load and the glucose threshold values listed for fasting, 1 hour, and 2 hours (Table 2, below); however, this test is not as well validated for detection of at-risk infants or mothers as the 100-g oral glucose tolerance test.

Table 1. Diagnosis of gestational diabetes mellitus with a 100-g oral glucose load

	mg/dL	mmol/L
Fasting	95	5.3
1-h	180	10.0
2-h	155	8.6
3-h	140	7.8

Two or more of the venous plasma concentrations must be met or exceeded for a positive diagnosis. The test should be done in the morning after an overnight fast of between 8 and 14 h and after at least 3 days of unrestricted diet (>150 g carbohydrate per day) and unlimited physical activity. The subject should remain seated and should not smoke throughout the test.

Table 2. Diagnosis of gestational diabetes mellitus with a 75-g oral glucose load

	mg/dL	mmol/L
Fasting	95	5.3
1-h	180	10.0
2-h	155	8.6

Information on obstetric and perinatal considerations can be found in the original guideline document.

Monitoring

Maternal metabolic surveillance should be directed at detecting hyperglycemia severe enough to increase risks to the fetus. Daily self-monitoring of blood glucose (SMBG) appears to be superior to intermittent office monitoring of plasma glucose. For women treated with insulin, limited evidence indicates that postprandial monitoring is superior to preprandial monitoring. However, the success of either approach depends on the glycemic targets that are set and achieved.
Urine glucose monitoring is not useful in gestational diabetes mellitus. Urine ketone monitoring may be useful in detecting insufficient caloric or carbohydrate intake in women treated with calorie restriction.
Maternal surveillance should include blood pressure and urine protein monitoring to detect hypertensive disorders.
Increased surveillance for pregnancies at risk for fetal demise is appropriate, particularly when fasting glucose levels exceed 105 mg/dL (5.8 mmol/L) or pregnancy progresses past term. The initiation, frequency, and specific techniques used to assess fetal well-being will depend on the cumulative risk the fetus bears from gestational diabetes mellitus and any other medical/obstetric conditions present.
Assessment for asymmetric fetal growth by ultrasonography, particularly in early third trimester, may aid in identifying fetuses that can benefit from maternal insulin therapy (see below).

Management

All women with gestational diabetes mellitus should receive nutritional counseling, by a registered dietitian when possible, consistent with the recommendations by the American Diabetes Association. Individualization of medical nutrition therapy depending on maternal weight and height is recommended. Medical nutrition therapy should include the provision of adequate calories and nutrients to meet the needs of pregnancy and should be consistent with the maternal blood glucose goals that have been established. Noncaloric sweeteners may be used in moderation.
For obese women (body mass index >30), a 30 to 33% calorie restriction (to ~25 kcal/kg actual weight per day) has been shown to reduce hyperglycemia and plasma triglycerides with no increase in ketonuria (Franz et al., 1994). Restriction of carbohydrates to 35 to 40% of calories has been shown to decrease maternal glucose levels and improve maternal and fetal outcomes (Major et al., 1998).
Insulin is the pharmacologic therapy that has most consistently been shown to reduce fetal morbidities when added to medical nutrition therapy (MNT). Selection of pregnancies for insulin therapy can be based on measures of maternal glycemia with or without assessment of fetal growth characteristics. When maternal glucose levels are used, insulin therapy is recommended when medical nutrition therapy fails to maintain self-monitored glucose at the following levels:
Fasting plasma glucose <105 mg/dL (5.8 mmol/L)

or

1-hour postprandial plasma glucose <155 mg/dL (8.6 mmol/L)

or

2-hour postprandial plasma glucose <130 mg/dL (7.2 mmol/L)
Measurement of the fetal abdominal circumference early in the third trimester can identify a large subset of infants with no excess risk of macrosomia in the absence of maternal insulin therapy. This approach has been tested primarily in pregnancies with maternal fasting serum glucose levels less than 105 mg/dL (5.8 mmol/L).
Human insulin should be used when insulin is prescribed, and self-monitoring of blood glucose should guide the doses and timing of the insulin regimen.
Programs of moderate physical exercise have been shown to lower maternal glucose concentrations in women with gestational diabetes mellitus. Although the impact of exercise on neonatal complications awaits rigorous clinical trials, the beneficial glucose-lowering effects warrant a recommendation that women without medical or obstetrical contraindications be encouraged to start or continue a program of moderate exercise as a part of treatment for gestational diabetes mellitus.
Gestational diabetes mellitus is not of itself an indication for cesarean delivery or for delivery before 38 completed weeks of gestation. Prolongation of gestation past 38 weeks increases the risk of fetal macrosomia without reducing cesarean rates, so that delivery during the 38th week is recommended unless obstetric considerations dictate otherwise.
Breast-feeding, as always, should be encouraged in women with gestational diabetes mellitus.

Long-term Therapeutic Considerations

Reclassification of maternal glycemic status should be performed at least 6 weeks after delivery and according to the guidelines of the "Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus." See Table 3 in the original guideline document for diagnostic criteria.
If glucose levels are normal postpartum, reassessment of glycemia should be undertaken at a minimum of 3-year intervals.
Women with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT) in the postpartum period should be tested for diabetes annually; these patients should receive intensive medical nutrition therapy and should be placed on an individualized exercise program because of their very high risk for development of diabetes.
All patients with prior gestational diabetes mellitus should be educated regarding lifestyle modifications that lessen insulin resistance, including maintenance of normal body weight through medical nutrition therapy and physical activity. Medications that worsen insulin resistance (e.g., glucocorticoids, nicotinic acid) should be avoided if possible. Patients should be advised to seek medical attention if they develop symptoms suggestive of hyperglycemia. Education should also include the need for family planning to assure optimal glycemic regulation from the start of any subsequent pregnancy. Low-dose estrogen-progestogen oral contraceptives may be used in women with prior histories of gestational diabetes mellitus, as long as no medical contraindications exist.
Offspring of women with gestational diabetes mellitus should be followed closely for the development of obesity and/or abnormalities of glucose tolerance.