Gestational diabetes is an abnormal increase in blood sugar (glucose) levels that can develop during pregnancy in women who do not already have diabetes. Blood glucose levels usually return to normal soon after birth. Women who have had gestational diabetes are at greater risk for Type 2 diabetes.
According to the U.S. Centers for Disease Control and Prevention, between 2% and 10% of women develop gestational diabetes. Prevalence has been increasing and is expected to continue increasing due to the larger number of pregnant women with risk factors for diabetes in general.
Race and ethnicity strongly affect the rate of development of gestational diabetes. Only about 1.4%–2% of Caucasian women develop gestational diabetes, whereas as many as 15% of Native American women from tribes in the Southwest United States develop the disorder. Between 5% and 8% of Hispanic Americans, African Americans, and Asian Americans develop gestational diabetes. If a woman experiences gestational diabetes, the chance of her developing it again in future pregnancies is as high as 68%.
Carbohydrates (sugars and starches) found in foods such as sweets, potatoes, pasta, and breads, are broken down during digestion into glucose, a simple sugar that circulates in the blood and is used by cells for energy. The level of glucose changes depends on the type and quantity of foods a person eats. Glucose level usually is highest about two hours after a meal. For the body to remain healthy, blood glucose levels must stay stable within certain narrow limits. In healthy people, the hormone insulin regulates the blood glucose level by controlling how much glucose enters cells. Once in cells, glucose either is used to meet the immediate energy needs of the cell or stored in liver, muscle, or fat cells for later release when blood glucose levels are low. In people with diabetes, this regulatory mechanism does not function correctly, and glucose builds up in the blood, a condition called hyperglycemia.
In Type 2 diabetes, the pancreas makes enough insulin, but cells become unresponsive to it, a condition called insulin resistance. As a result, adequate amounts of glucose cannot enter these cells, and glucose builds up in the blood. Many people withType 2 diabetes can control their blood glucose level through diet and exercise. Others must take supplemental insulin either by mouth (orally) or by injection.
In gestational diabetes, the pancreas makes insulin, but the placenta, which allows the fetus to obtain nourishment, produces hormones (e.g., estrogens, progesterone, and chorionic somatomammotropin) that increase the insulin resistance of cells. These hormones are at their highest levels during the third trimester of pregnancy. Their presence reduces the amount of glucose that can enter cells, so that more remains in the blood, and hyperglycemia occurs. Most pregnant women do not develop gestational diabetes because the pancreas produces additional quantities of insulin (as much as 50% more than normal in the third trimester) to compensate for insulin resistance caused by pregnancy hormones. When a mother's pancreas cannot produce enough extra insulin, blood levels of glucose stay abnormally high, and she develops gestational diabetes.
Women at risk for gestational diabetes include those who:
Because increasing levels of pregnancy hormones cause gestational diabetes, it develops late in pregnancy when pregnancy hormones are at their highest levels. Often women with gestational diabetes have few symptoms. Left untreated, the mother's blood glucose levels will remain consistently high, and these same high levels will occur in the blood of the fetus. The fetal pancreas responds to the high glucose levels by secreting large amounts of insulin. This insulin allows the fetal cells to take in excess glucose that is converted into fat and stored. This conversion process uses oxygen that may be needed for other fetal processes. Low oxygen levels can lead to an increased risk of heart, breathing, and vision problems. Increased fat storage causes many babies born to women with gestational diabetes to be unusually large, often large enough to cause more difficult deliveries that may require the use of forceps, suction, or cesarean section.
Furthermore, when the baby is born, he or she will have an abnormally high level of insulin in the blood. After birth, when the mother and baby are no longer attached to each other via the placenta and umbilical cord, the baby will no longer be receiving the mother's high level of blood glucose. The infant's high level of insulin, however, will quickly use up the glucose circulating in the infant's bloodstream. The baby is then at risk for having a dangerously low level of blood glucose, a condition called hypoglycemia. When this occurs, it is easily resolved by giving the baby glucose from an external source.
Because gestational diabetes often exists with no symptoms detectable by the mother, and because its existence puts the developing baby at risk for developmental abnormalities, screening for the disorder is a routine part of pregnancy care. This screening usually is done between the 24th and 28th week of pregnancy. At this point in the pregnancy, the placental hormones have reached a sufficient level to cause insulin resistance. Screening for gestational diabetes 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 of less than 140 mg/dL is considered normal.
If an expectant mother is diagnosed with gestational diabetes, she needs to watch her intake of sugars and other carbohydrates. This is vital because this type of diabetes not only affects the mother, it also affects the unborn child. Healthcare providers give women who develop gestational diabetes a suggested diet to help control glucose levels in the blood.
Prognosis for women with gestational diabetes and their infants is generally good. Almost all such women have blood glucose levels that return to normal after the birth of their baby. Research has shown, however, that nearly half of the women who have gestational diabetes develop Type 2 diabetes within 15 years.
Serious complications can develop for the pregnant woman and fetus if gestational diabetes is not appropriately managed, including the following:
Pregnant women who have Type 1 or Type 2 diabetes that is poorly controlled also have four to eight times the chance of having a baby born with a birth defect than women who do not have diabetes. The risk is much lower for babies born to women who develop gestational diabetes because their fetus is exposed to high glucose levels for a much shorter time and only near the end of pregnancy after most organs are already formed. The child of a mother with gestational diabetes has a greater than normal chance of developing diabetes sometime in adulthood. A woman who has had gestational diabetes during one pregnancy has an approximately 68% chance of having it again during any subsequent pregnancies. Women who had gestational diabetes usually have their blood glucose levels tested at the postpartum checkup and/or after stopping breastfeeding.
As of 2018, research has not found a way to prevent gestational diabetes because it is caused by the effects of normal hormones of pregnancy. The effects of insulin resistance can be best handled through careful attention to diet, avoiding becoming overweight throughout life, participating in reasonable exercise, and avoiding smoking.
See also American Diabetes Association ; Bernstein diet ; Diabetes mellitus ; Diabetic diet ; Insulin ; Metabolic syndrome ; Obesity ; Sugar .
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Rosalyn Carson-DeWitt, MD
Revised by Jennifer E. Van Pelt, MA