Diabetes Mellitus in Pregnancy

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Chapter 206 Diabetes Mellitus in Pregnancy

THE CHALLENGE

To diagnose and manage disturbances of glucose metabolism to minimize the risk to mother and fetus associated with diabetes. Diabetes and pregnancy have profound effects on each other, making a familiarity with the interactions between mother, fetus, and the diabetic process a requirement to provide optimal care.

Scope of the Problem: Diabetes mellitus is the most common medical complication of pregnancy, affecting 2% to 5% of patients (varying in direct proportion to the prevalence of type 2 diabetes in a given population or ethnic group). Patients who had gestational diabetes in a previous pregnancy have a 33% to 50% likelihood of recurrence in a subsequent pregnancy. Patients with type 1 diabetes are at greater risk for maternal complications (diabetic ketoacidosis, glucosuria, hyperglycemia, polyhydramnios, pre-eclampsia, pregnancy-induced hypertension, preterm labor, retinopathy, urinary tract infections, postpartum uterine atony). The offspring of women with diabetes have a 3-fold greater risk of congenital anomalies (3% to 6%) than children of mothers without diabetes (1% to 2%). Most common among these anomalies are cardiac and limb deformities. Other fetal complications include fetal demise, hydramnios, hyperbilirubinemia, hypocalcemia, hypoglycemia, macrosomia, polycythemia, prematur-ity, respiratory distress syndrome, and spontaneous abortion.

Objectives of Management: To return serum glucose levels to as close to normal as possible through a combination of diet, exercise, oral hypoglycemic agents, and insulin (for selected patients). Optimal management of diabetes begins before pregnancy. Optimal management also requires patient and family education and involvement. For the established patient with diabetes, this teaching is directed to the need for tighter control and more frequent monitoring. The woman with newly diagnosed diabetes requires general instruction about her disease and the unique aspects of diabetes during pregnancy. From the standpoint of the fetus, the goal of treatment is to reduce the likelihood of macrosomia and its consequences; neonatal hypoglycemia also may be reduced.

TACTICS

Relevant Pathophysiology: Human placental lactogen, made in abundance by the growing placenta, promotes lipolysis and decreases glucose uptake and gluconeogenesis. This anti-insulin effect is sufficient to tip borderline patients into a diabetic state or prompt readjustments in the insulin dosage used by patients with insulin-dependent diabetes. Estrogen, progesterone, and placental insulinase further complicate the management of diabetes, making diabetic ketoacidosis more common. High renal plasma flow and diffusion rates that exceed tubular reabsorption result in a physiologic glucosuria of approximately 300 mg/day. This physiologic glucosuria, combined with the poor correlation between urinary glucose and blood glucose levels, makes the urinary glucose screening useless to detect or monitor diabetes during pregnancy.

Strategies: The severity of diabetes may be classified by either the American Diabetes Association (ADA) classification or by the White classification schemes, although the latter has been rendered less useful by improvements in fetal assessment, neonatal care, and the metabolic management of the pregnant patient. The use of these classifications makes comparisons of published data meaningful and may help to predict the relative risk to the pregnant mother and fetus. Patients with American Diabetes Association-defined type 2 disease are often overweight and their diabetes may be controlled with strict diet or with minimal oral hypoglycemic agent or insulin therapy. Gestational diabetes is reversible, although these patients have a greater incidence of glucose intolerance in subsequent pregnancies or with aging. Because of the increased risk of fetal anomalies, a determination of maternal serum α-fetoprotein and early ultrasonographic studies are of greater importance for these patients. Antenatal testing and active management of late pregnancy and labor induction are all indicated for selected patients with diabetes. When there is an estimated fetal weight of 4500 g or more, cesarean delivery may be considered because it may reduce the likelihood of permanent brachial plexus injury in the infant.

Patient Education: American College of Obstetricians and Gynecologists Patient Education Pamphlet AP051 (Diabetes and Pregnancy).

IMPLEMENTATION

Special Considerations: Screening for gestational diabetes is carried out by measurement of plasma glucose level 1 hour after ingestion of a 50-g glucose load, performed between 24 and 28 weeks of gestation. (Jellybeans can be substituted for the usual glucose beverage—28 standard-sized jellybeans = 50 g simple carbohydrate—but this method has poor sensitivity [40%] when compared with glucose polymer solutions [80% to 90%]) The upper limit of normal for such a test is 130 mg/dL. (A screening test threshold of 140 mg/dL has 10% less sensitivity than a threshold of 130 mg/dL but fewer false-positive results; either threshold is acceptable.) If a patient’s value exceeds this threshold, a formal 3-hour glucose tolerance test is performed. About 15% of patients have an abnormal screening test, and about the same proportion have an abnormal 3-hour test. For a 3-hour glucose tolerance test, the patient must ingest a minimum of 150 g/day of glucose for the 3 days preceding the test. A fasting glucose level is determined, and a 100-g glucose load is consumed. Plasma glucose levels are then measured at 1, 2, and 3 hours. If two or more values are abnormal, the diagnosis of gestational diabetes may be made. If only one value is abnormal, the test is considered equivocal and should be repeated in 4 to 6 weeks. Studies indicate that screening may be omitted for selected individuals who are very low risk by selection criteria (see box).

Individuals at Low Risk for Gestational Diabetes (Must Meet All Criteria)

• Age younger than 25 years

• No known diabetes in first-degree relative

• Not a member of an ethnic group with an increased risk for the development of type 2 diabetes (examples of high-risk ethnic groups include women of Hispanic, African, Native American, South or East Asian, or Pacific Islands ancestry)

• Body mass index of 25 or less

• No previous history of abnormal glucose tolerance

• No previous history of adverse obstetric outcomes usually associated with gestational diabetes mellitus

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