Gestational diabetes mellitus (GDM) is a condition that occurs during pregnancy . Like other forms of diabetes, GDM involves a defect in the way the body processes and uses sugars (glucose) in the diet. Gestational diabetes, however, has a number of characteristics that are different from other forms of diabetes. This form of diabetes does not include women who are diabetic before they become pregnant. Gestational diabetes usually occurs in the second and third trimesters of the pregnancy.
Glucose is a form of sugar that is present in many foods, including sweets, potatoes, pasta, and breads. The body uses glucose to provide energy. It is stored in the liver , muscles, and fatty tissue. The pancreas produces a hormone (a chemical produced in one part of the body that travels to another part of the body in order to exert its effect) called insulin. Insulin is required to allow glucose to enter the liver, muscles, and fatty tissues, thus reducing the amount of glucose in the blood . In persons with diabetes, blood levels of glucose remain abnormally high. The inability of the pancreas to produce enough insulin is the cause of these high levels of glucose.
In gestational diabetes, the pancreas is not at fault. The problem is in the placenta. During pregnancy, the placenta provides the baby with nourishment. It also produces a number of hormones that interfere with the body's usual response to insulin. This condition is referred to as "insulin resistance." The development of insulin resistance is primarily caused by a substance called lactogen, which is produced during pregnancy, and from increased blood levels of the hormones progesterone and estrogen. The blood levels of these substances tend to peak in the second and third trimester of the pregnancy, which is when GDM is most likely to occur. Most pregnant women do not develop GDM because the pancreas works to produce extra quantities of insulin to compensate for insulin resistance. However, when a woman's pancreas cannot produce enough extra insulin, blood levels of glucose remain abnormally elevated, and the woman is considered to have GDM. It is believed that some women with borderline blood sugar problems before pregnancy are more likely to have long-term blood sugar regulation problems after developing GDM.
As of January 2001, about 200,000, or 7%, of pregnant women in the United States develop GDM every year. Women at risk for GDM include those who:
- are overweight
- have immediate family members with a history of Type II diabetes
- have previously given birth to a large (over 9 lbs [4 kg]) baby
- have previously had a baby who was stillborn, or born with a birth defect
- have an excess amount of amniotic fluid (the cushioning fluid within the uterus that surrounds the developing fetus)
- are over 25 years of age
- belong to an ethnic group proved to experience higher rates of GDM. (In the United States, these groups include Hispanic-Americans, American Indians, and African-Americans, as well as individuals from Asia, India, and the Pacific Islands.)
- have had GDM during a previous pregnancy
- have persistent evidence of excess glucose in the urine
- have a history of chronic drug abuse involving agents such as corticosteroids
Causes and symptoms
Most women with GDM have no recognizable symptoms. However, leaving GDM undiagnosed and untreated is dangerous to the developing fetus. Left untreated, a woman with diabetes will have consistently high blood sugar. This sugar will cross the placenta and the unborn baby's pancreas will respond to this high level of sugar by constantly producing large amounts of insulin. The insulin will allow the cells of the fetus to take in glucose, where it will be converted to fat and stored. A fetus that has been exposed to consistently high levels of sugar may be abnormally large. Such a baby may grow so large that he or she cannot be born through the vagina, but will instead need to be born through a surgical procedure (cesarean section).
Furthermore, when the baby is born, the baby will still have an abnormally large amount of insulin circulating in the blood. After birth, when the mother and baby are no longer connected via the placenta and umbilical cord, the baby will no longer be receiving the mother's high level of sugar. The baby's high level of insulin, however, will very quickly use up the glucose circulating in the its bloodstream, predisposing the baby to a dangerously low level of blood glucose (i.e., a condition called hypoglycemia).
Since GDM most often exists with no symptoms detectable by the patient, and since its existence puts the developing baby at considerable risk, screening for the disorder is a routine part of prenatal care . This screening is usually done between the 24th and 28th week of pregnancy. By this point in the pregnancy, the placental hormones have reached a sufficient level to cause insulin resistance. Screening for GDM involves the pregnant woman drinking a special solution that contains exactly 50 grams of glucose. An hour later, the woman's blood is drawn and tested for its glucose level. A level less than 130-140 mg/dl is considered normal.
When the screening glucose level is over the safe level, a special three-hour glucose tolerance test is performed. This involves following a special diet for three
days prior to the test. This diet is designed to contain at least 150 grams of carbohydrate each day. Just before the test, the patient is instructed to eat and drink nothing (except water) for 8–14 hours. A blood sample is then tested to determine the fasting glucose level. The patient then drinks a special solution containing exactly 100 grams of glucose, and her blood is tested every hour for the next three hours. If two or more of these levels are elevated over normal, the patient is considered to have GDM.
Treatment for GDM will depend on the severity of the diabetes. Mild forms can be treated with diet (i.e., decreasing the intake of sugars and fats ). Many women are put on strict, detailed diets, and are asked to stay within a certain range of calorie intake. Exercise is sometimes used to keep blood sugar levels lower. Patients are often asked to regularly measure their blood sugar. This
Corticosteroids —Hormonal steroid substances that originate in the cortex of the adrenal gland.
Estrogen —A female sex hormone responsible for secondary sexual characteristics and cyclic changes in women.
Glucose —A form of sugar. The final product of the breakdown of carbohydrates (starches).
Insulin —A hormone produced by the pancreas that is central to the processing of sugars and carbohydrates in the diet.
Ketoacidosis —Excessive acidic condition in the body caused by excess production of ketone bodies.
Lactogen —A substance that stimulates the production of milk in female animals.
Placenta —An organ that is attached to the inside wall of the mother's uterus and to the fetus via the umbilical cord. The placenta allows oxygen and nutrients from the mother's bloodstream to pass into the unborn baby.
Progesterone —A hormone that is responsible for the changes that occur in the second half of the menstrual cycle.
is done by poking a finger with a needle called a lancet, putting a drop of blood on a special type of paper, and feeding the paper into a meter that analyzes and reads the blood sugar level. When diet and exercise do not keep blood glucose levels within an acceptable range, a patient may need to take regular shots of insulin.
Many babies born to women with GDM are large enough to cause more difficult deliveries, and they may require the use of cesarean section. Once the baby is born, it is important to carefully monitor its blood glucose levels. These levels may drop sharply and dangerously once the baby is no longer receiving large quantities of sugar from the mother. When this occurs, it is easily resolved by giving the baby glucose.
Prognosis for women with GDM, and their babies, is generally good. Mothers who develop GDM need to be evaluated for glucose intolerance six to eight weeks after the birth of the baby. This evaluation usually involves a two-hour oral glucose tolerance test with 75 grams of glucose, although follow-up methods may vary. Almost all such women stop being diabetic after the baby's birth. However, clinicians have also demonstrated that nearly 50% of these women will develop a permanent form of diabetes within 15 years. A woman who has had GDM during one pregnancy has about a 66% chance of having it again during any subsequent pregnancies. In addition, women with GDM are at increased risk for developing complications, such as infections, temporary low blood sugar, high blood pressure , and ketoacidosis.
Health care team roles
Women with GDM will likely be evaluated and treated by a variety of personnel in the allied health field. The obstetric nurse, physician, or nurse midwife will gather a detailed medical history, which may provide information suggesting the patient is at increased risk for developing GDM. Laboratory technicians play an important role in the diagnosis of GDM by testing urine and blood for excessive glucose levels. An amniocentesis conducted by an imaging technician is often performed in women with GDM because of the potential abnormal growth changes in the fetus.
Most patients with GDM can manage their blood sugar levels through dietary changes. A nutritional therapist plays a critical role in planning a regimen for these women. An exercise therapist can also play a significant role in the prevention and ongoing treatment of women with GDM. Exercise can help prevent excessive weight gain by the mother, which can reduce the severity of the diabetes. In addition, exercise tends to normalize blood glucose levels. If the patient requires insulin, then the nurse or physician will generally instruct the patient on how to administer the insulin. The nurse will also likely advise on how to perform blood glucose monitoring. The pharmacist can play a role in the education of the patient in this matter as well.
There is no known way to actually prevent GDM, particularly since this condition is due to the effects of normal hormones of pregnancy. However, the effects of insulin resistance can be best handled through careful attention to diet, avoiding becoming overweight throughout life, and participating in a reasonable exercise program.
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American Diabetes Association, 1660 Duke Street, Alexandria, VA 22314. (800) DIABETES (800) 342-2383. <http://www.diabetes.org>.
Mark A. Mitchell