Diabetes Mellitus & Pregnancy: Gestational & Overt

KEY FEATURES

Essentials of Diagnosis

• Gestational diabetes

  • Abnormal glucose tolerance in pregnancy

  • Believed to be an exaggeration of the pregnancy-induced physiologic changes in carbohydrate metabolism

• Overt diabetes

  • Diabetes mellitus that antedates the pregnancy

  • Diagnosed in 50% of women with gestational diabetes at some point in their lifetime

General Considerations

• Normal pregnancy can be characterized as a state of increased insulin resistance that helps ensure a steady stream of glucose delivery to the developing fetus

  • Thus, both mild fasting hypoglycemia and postprandial hyperglycemia are physiologic

• Gestational diabetes

  • Principal concern is excessive fetal growth, which can cause increased maternal and perinatal morbidity

• Overt diabetes

  • In addition to fetal overgrowth, there is increased frequency of

    • Spontaneous pregnancy losses and third-trimester stillbirths

    • Increased risk for fetal malformations, especially cardiac, skeletal, and neural tube defects

    • For the mother, the likelihood of infections and pregnancy-related hypertension is increased

  • Women whose periconceptional glycosylated hemoglobin levels are at or near normal levels have rates of malformations that approach baseline

• Women with diabetes should undergo preconception counseling and evaluation to maximize pregnancy outcomes

• All pregnant women should undergo screening for gestational diabetes mellitus, either by history, clinical risk factors, or (most commonly) laboratory screening tests

• Throughout the pregnancy, women with diabetes should be seen by a health care provider every 2–3 weeks and more often depending on the clinical condition

CLINICAL FINDINGS

Symptoms and Signs

• Excessive fetal growth

• Shoulder dystocia

• Preeclampsia

• Macrosomia

• Hypertension is common in overt diabetes

• Signs and symptoms of infections should be evaluated and promptly treated

Differential Diagnosis

• Drugs: corticosteroids, thiazides, tacrolimus

• Diabetes insipidus

• Psychogenic polydipsia

• Nondiabetic glycosuria (benign)

DIAGNOSIS

Laboratory Tests

• Euglycemia is 60–90 mg/dL (3.3–5.0 mmol/L) while fasting and < 120 mg/dL (< 6.7 mmol/L) 2 hours postprandially

For Gestational Diabetes

• Screen for gestational diabetes after 24 weeks’ gestation

• Two-stage testing strategy is recommended by the American College of Obstetricians and Gynecologists

  • A screening 50-g glucose load is administered at 24–28 weeks' gestation

  • If this test is abnormal, the diagnostic test is a 100-g oral glucose tolerance test (Table 21–4)