Best Dx/Best Rx: Gestational Diabetes Mellitus

Gestational Diabetes Mellitus

Ellen W. Seely, MD
Chloe A. Zera, MD
Brigham and Women's Hospital, Harvard Medical School, Boston, MA

Definition/Key Clinical Features
Differential Diagnosis
Best Tests
Best Therapy
Best References

Definition/Key Clinical Features

Glucose intolerance first identified during pregnancy
Affects at least 5% of pregnant women in the United States, and incidence is increasing
Diabetes resolves after delivery if the diagnosis of gestational diabetes mellitus (GDM) was correct and patient did not have preexisting undiagnosed type 2 diabetes mellitus
Associated with high risk of GDM in future pregnancies as well as future type 2 diabetes mellitus (~ 50% within 5 yr)
Risks to fetus if glucoses are uncontrolled include macrosomia, neonatal hypoglycemia, neonatal jaundice, perinatal mortality, and childhood obesity
Treatment of GDM improves pregnancy outcomes

Differential Diagnosis

Type 2 diabetes
Type 1 diabetes

Best Tests

Several accepted testing strategies; most frequent in United States is two-step process
Two-step testing (endorsed by ACOG)

Glucose challenge test (GCT): measure plasma glucose level 1 hr after ingestion of 50 g glucose
If plasma glucose exceeds chosen threshold on GCT, perform 3 hr 100 g oral glucose tolerance test (OGTT); see criteria below in Table 1

One-step testing (endorsed by IADPSG)

75 g oral glucose tolerance test (OGTT); see criteria in Table 1

Table 1 Comparison of Third-Trimester GDM Diagnostic Strategies

Recommendation (Year)	Test	Glucose Thresholds	Population
ACOG22,25	100 g OGTT	2 or more abnormal values by either of the following criteria: 1. NDDG Fasting ≥ 105 mg/dL 1 hr ≥ 190 mg/dL 2 hr ≥ 165 mg/dL 3 hr > 145 mg/dL or 2. Carpenter-Coustan: Fasting ≥ 95 mg/dL or 1 hr ≥ 180 mg/dL or 2 hr ≥ 155 mg/dL 3 hr > 140 mg/dL	Risk based, but "universal screening may be more practical approach"
WHO21	75 g OGTT	Fasting ≥ 126 mg/dL or 2 hr ≥ 200 mg/dL	Risk based
IADPSG25	75 g OGTT	Fasting ≥ 92 mg/dL or 1 hr ≥ 180 mg/dL or 2 hr ≥ 153 mg/dL	Universal
ADA2	75 g OGTT	Fasting ≥ 92 mg/dL or 1 hr ≥ 180 mg/dL or 2 hr ≥ 153 mg/dL	Universal

ACOG = American College of Obstetrics and Gynecology; IADPSG = International Association of Diabetes and Pregnancy Study Groups; NDDG = National Diabetes Data Group; WHO = World Health Organization.

Best Therapy*

Randomized trials have demonstrated a benefit to pregnancy outcomes with treatment of GDM with medical nutrition therapy and insulin as required
There are no randomized trials to identify blood glucose targets to prevent perinatal morbidity, but some evidence supports use of the following targets:

Fasting capillary blood glucose < 96 mg/dL, 1 hr postprandial < 140 mg/dL, 2 hr postprandial < 120 mg/dL

Blood Glucose Monitoring

Self-testing of capillary blood glucose

Lifestyle Measures

Nutrition

Medical nutrition therapy (MNT) is the cornerstone of GDM management
Weight gain

Prepregnancy body mass index (BMI) ≥ 30 kg/m2: limit gain to 20 lb
Prepregnancy BMI 25 to < 30 kg/m2: limit gain to 25 lb
Prepregnancy BMI 18.5 to < 25 kg/m2: limit gain to 35 lb
Prepregnancy BMI < 18.5 kg/m2: limit gain to 40 lb
If desired weight gain achieved by the time of diagnosis, safe to restrict intake to 25 kcal/kg

Exercise

Assess baseline health and physical capacity
Goal of 30 minutes per day of moderate physical activity in women without contraindications

Insulin Therapy

Recommended if glycemic targets not achieved or maintained via MNT alone
Common regimen: NPH insulin plus premeal short-acting insulin analogues aspart or lyspro to control fasting and postprandial hyperglycemia

Oral Antihyperglycemic Agents

Glyburide

Alternative to insulin therapy
Monitor glucose levels closely to ensure adequate glycemic control
Minimal placental transfer
Not approved by Food and Drug Administration (FDA) for use in pregnancy

Metformin:

Alternative to insulin or adjunct to insulin
Monitor glucose levels closely to ensure adequate glycemic control
Crosses placenta freely, but some data suggest safety in exposed infants
Up to 50% of women on metformin will need supplemental insulin
Not FDA approved for use in pregnancy

Follow-up

Measure fasting blood glucose shortly after delivery and perform an OGTT at 6 wk postpartum
Assess at least every 3 years for diabetes
Perform OGTT before subsequent pregnancies
Use appropriate diabetes prevention measures

Best References

Metzger BE, et al: Diabetes Care 21(suppl 2):B161, 1998 PMID 9704245

Crowther CA, et al: N Engl J Med 352:2477, 2005 PMID 15951574

Langer O, et al: N Engl J Med 343:1134, 2000 PMID 11036118

* To obtain additional drug information, click on the DrugInfo tab in the left column, or click on the following link: http://search.medscape.com/drug-reference-search?queryText=

December 2011