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Gestational Diabetes

From Atlanta Maternal-Fetal Medicine 

INTRODUCTION

Gestational diabetes is one of the most common complications seen by obstetricians during pregnancy. It affects nearly one out of every thirty patients delivered. This issue will discuss the methods for diagnosing gestational diabetes, usual recommended therapies, and issues regarding fetal health.

BACKGROUND

For more than a century, obstetricians have been aware that patients with pre-existing diabetes who became pregnant worsened clinically. Blood sugar values of these diabetic patients were very unpredictable. Prior to the invention of insulin, patients with diabetes were advised by their physicians not to conceive. There was a significant risk of maternal death from diabetes if patients attempted pregnancy. After the invention of insulin, the risk of maternal death dropped dramatically in the era before World War II, but diabetic patients continued to have a much higher risk of both fetal death and fetal birth defects.

During the second half of the twenty-first century, physicians began to recognize a form of diabetes that was unique to pregnancy (gestational diabetes). In general, these patients are non-diabetic prior to pregnancy and after delivery. However, hormone changes during pregnancy alter the body's ability to handle sugar metabolism, resulting in a "temporary" diabetic condition during the pregnancy. Gestational diabetes cannot be recognized by symptoms, since the symptoms of diabetes (loss of energy, intense thirst, frequent urination) are common in normal pregnant women. As a result, universal screening for gestational diabetes is recommended during pregnancy.

Patients who have gestational diabetes have an increased risk of three complications: large babies, cesarean delivery, and stillbirth. Recognition and treatment of patients with gestational diabetes is designed to minimize these complications, and improve pregnancy outcome for these patients.

INSULIN RESISTANCE

Patients who have pre-existing diabetes have an insulin deficiency that is usually related to decreased function of the pancreas gland. Patients with gestational diabetes usually have normal insulin levels, but the insulin is less effective. During pregnancy, their bodies are "resistant" to insulin. Because of this, patients with gestational diabetes often have normal blood sugar values before meals, but have abnormally high blood sugar values after meals. This "resistance" to insulin improves dramatically after the delivery of the baby(s). Complications attributed to gestational diabetes are thought to result from high blood sugar values after meals during the latter half of pregnancy.

DIAGNOSIS

Less than one percent of patients who present for a new obstetric visit have pre-existing diabetes. The incidence of pre-existing maternal diabetes has increased slightly during the latter half of the twentieth century, primarily because of advancing maternal age and increased maternal weight.

Routine screening for gestational diabetes has been recommended for nearly twenty years. The generally-accepted screening test for gestational diabetes for non-diabetic pregnant patients is called a gestational glucose screen, or rapid glucose screen. It was first proposed by Dr. Coustan of Yale University. Approximately ninety-percent of patients will have a normal rapid glucose screen. These patients have an extremely low risk of developing gestational diabetes during pregnancy.

A gestational diabetes screening is a simple test where patients take fifty grams of sugar (dextrose) either mixed with orange flavoring, or as jelly beans. One hour following ingestion of this sugar, the patient's blood sugar is checked by the laboratory. Patients do not have to be fasting for the test. Patients are not advised to restrict themselves from sugar before this test. If the patient's blood sugar value is less than 140 mg% one hour after the sugar, then the sugar test is considered to be normal.

Patients who have greatly elevated blood sugar values for a gestational glucose screen are usually diagnosed with gestational diabetes based on this single test. Suggested values for the diagnosis of gestational diabetes based solely on rapid glucose screen have ranged from 180 to 200 mg%.

For patients whose blood sugar results are in the intermediate range (140-200 mg%), it is advisable to perform a more accurate diagnostic test. Usually, patients have a formal three-hour glucose tolerance test performed if their glucose is in the intermediate range. The three-hour glucose tolerance test requires that patients eat a moderate amount of sugar and carbohydrates for three days prior to the test. The test is performed after a six-hour fast. Patients have a blood sugar drawn in the fasting state. Following this, patients ingest twice as much sugar as in the rapid glucose screen (100 gm). If the fasting blood sugar of the patient is elevated, then the diagnosis of gestational diabetes can be made. If the fasting blood sugar is normal, then the diagnosis of glucose intolerance is as follows:

1.) A single abnormal value is considered to be normal.

2.) Two or more elevated values is considered to be abnormal.

3.) An elevated fasting blood sugar in conjunction with another abnormal value is considered to be a more severe form of gestational diabetes (Class A2).

TREATMENT

Following the diagnosis of gestational diabetes, the patient should be evaluated for treatment.

Treatment for gestational diabetes involves three components; diet therapy, monitoring of blood sugars, and insulin therapy when needed. Patients are usually referred to a registered dietician for formal dietary counseling. The patient's diet recommendations are based on height and ideal body weight. Usual calorie ranges are 1800-2400 calories. The patient's calories are usually divided between three meals and three snacks. The registered dietician attempts to incorporate patient's food preferences into the diet plan.

The American Diabetes Association (ADA) and several support groups publish sample meal plans for patients with gestational diabetes so that they can be more creative in planning meals within their diet restrictions.

After patients have been on diet therapy for a minimum of one week, then blood sugar values are re-checked while on diet therapy to determine if the diet therapy has been successful in reducing the patient's blood sugar. If the patient's fasting blood sugars and after-eating (postprandial) blood sugars become normal on the diet, then no further therapy is required. Normal ranges for blood sugars on diet therapy are:

1.) Fasting blood sugar of less than 105 mg%

2.) Blood sugar values two hours after meals of less than 120 mg%

If diet therapy is successful in treating a patient's gestational diabetes, then follow-up visits are scheduled at a minimum of twice monthly. The patient's blood sugar values are checked periodically to assure that diet therapy continues to control their blood sugars. Dietary restrictions can be lifted following the patient's delivery.

If the patient's dietary therapy is unsuccessful in reducing the patient's blood sugars, then, either the patient's diet therapy needs to be re-evaluated, or insulin therapy should be suggested. Diet-controlled gestational diabetes is classified as A1 diabetes. Gestational diabetes requiring insulin therapy for control is classified as Class A2 diabetes. Insulin therapy for patients with gestational diabetes requires patient training. A significant number of patients have reservations about self-injection of insulin or monitoring of blood sugars. Training can be provided either in the physician's office, by a home-health care nursing service, or by a brief hospital admission. The choice of teaching methods should be tapered to the patient's needs. Goals for the patient's insulin therapy should be to minimize the number of injections that the patient will have to take on a daily basis, and to bring blood sugar values within suggested ranges.

ANTEPARTUM FETAL HEALTH TESTING

Patients with well-controlled Class A1 diabetes do not require fetal health testing. Research shows that their risk of perinatal loss is no different from the risk of perinatal loss in the general population (1 - 1.5 percent). Patients with insulin-dependent diabetes (Class A2) are thought to have an increased risk of stillbirth compared with the general population. Antepartum fetal health testing is indicated in these patients.

Antepartum fetal health testing can be explained to patients as a fetal health testing program, or a stillbirth prevention program. The program can be conducted using a variety of tests currently available, including non-stress test, contraction stress test, biophysical profile study, or the "modified biophysical profile study". In each case, there are well-established normal values for these tests. If the tests are reassuring, then the risk of stillbirth is low. However, should the test be non-reassuring, the patient should be considered for hospitalization or delivery. Fetal health tests are normally performed on a weekly basis. Patients with extremely poor control of their gestational diabetes may need testing on a twice-weekly basis.

TIMING OF DELIVERY

Patients with gestational diabetes are known to have an increased risk for adverse perinatal outcome if managed as post-term patients. Therefore, it is recommended that all patients with gestational diabetes be delivered by term. Certainly, the most favorable outcomes are achieved if the patient labors spontaneously prior to the due date. However, if a patient remains undelivered in the last week of pregnancy, induction of labor or cesarean section should be considered. A maturity amniocentesis test should be considered for patients with poorly-controlled diabetes, or for patients who are to be delivered prior to thirty-nine weeks' gestation. The patient's obstetrician should decide the method of labor induction, or the need for cesarean section.

POST DELIVERY CARE

Patients with Class A1 gestational diabetes normally experience resolution of their blood sugar problems immediately after delivery. For these patients, diet restrictions may be lifted immediately after delivery with no adverse consequences to the mother. Postpartum patients should be reminded that continuing their ADA diet may be beneficial, as forty-percent of gestational diabetic patients eventually develop clinical diabetes.

Patients with Class A2 diabetes should have their blood sugars monitored off insulin for the first few days following delivery. Some of these patients will be found to have underlying maternal diabetes and require continued care with insulin or oral agents. Normally, patients with true Class A2 diabetes will have resolution of their blood sugar problems within the first twenty-four to forty-eight hours following delivery. If blood sugars values become normal without insulin, then the obstetrician should recommend that the patient continue the ADA diet restrictions postpartum.

RETESTING AFTER DELIVERY

Long-term follow-up of gestational diabetes patients has revealed that many of these patients do have mild underlying glucose intolerance. Approximately forty percent of patients with gestational diabetes will develop adult-onset diabetes later in life.

It is recommended that patients have follow-up diabetes testing done after the resolution of their gestational diabetes. Follow-up testing may consist of a three-hour glucose tolerance test 6-8 weeks following delivery. An abbreviated form of this test, a two-hour glucose tolerance test using 75 mg of dextrose, can also be used to diagnosis diabetes in the postpartum state.

Patients who have normal fasting blood sugars but continue to demonstrate glucose intolerance would benefit from continued diabetic dietary restrictions. If the fasting blood sugar is elevated and the glucose tolerance test is abnormal, then the patient should be referred to her primary care physician or medical endocrinologist.

SUMMARY

Gestational diabetes is a common and significant complication of pregnancy. All patients who are pregnant should be tested for gestational diabetes. Patients whose gestational diabetes testing is abnormal should be treated initially with diet therapy. More severe cases of gestational diabetes may require insulin therapy, or antepartum fetal health testing. The majority of patients with gestational diabetes (more that 90 percent) will experience a complete resolution of their diabetes following delivery. Patients with gestational diabetes should be retested 6-8 weeks following their delivery to assure that their diabetes has truly resolved. With modern diagnosis and treatment, the risk of severe complications in patients with gestational diabetes can be minimized.