Gestational diabetes is a diabetic condition that occurs during pregnancy. Although women who develop gestational diabetes are at higher risk for developing diabetes mellitus later in life, gestational diabetes will resolve after the birth.
In diabetes, the body cannot properly metabolize glucose (simple sugar). Blood levels of insulin actually increase in pregnancy. (Insulin is the hormone that metabolizes glucose.) The body, however, becomes resistant to insulin’s effects. How this occurs is not entirely clear but may be an effect of pregnancy hormones: estrogen, progesterone, or human placental lactogen. The purpose of insulin resistance is quite likely to ensure an adequate supply of glucose for the fetus.
Gestational diabetes occurs in 1 to 3 percent of pregnancies in the United States. Risk factors include a family history of diabetes, obesity, age greater than 30, a history of a very large baby or a malformed or stillborn baby without apparent cause, or high blood pressure. Glucose appearing in the urine may signify gestational diabetes, but is not diagnostic.
With appropriate control of glucose levels, women with gestational diabetes do not experience fetal death more often than women without diabetes. The main problem seen in these babies is macrosomia-excessive growth. Because of their large size, babies born to women with gestational diabetes are more prone to injuries at birth, such as those that can occur when the shoulders are delivered with difficulty.
Experts do not agree on whether all women should be screened routinely for gestational diabetes or whether screening should be restricted to women at risk. Those who favor screening all women point out that as many as one-third to one half of women with gestational diabetes may be missed if screening were limited.
The screening test for gestational diabetes is called a glucose challenge test (GCT), or an oral glucose challenge test (OGCT), because the sugar is given by mouth. Women drink a solution containing 50 grams of glucose, usually in the form of a very sweet carbonated beverage. Blood is drawn 1 hour after the woman drinks the soda. The GCT is performed between 24 and 28 weeks of gestation. If you have risks for diabetes, it may be performed earlier and repeated between 24 and 28 weeks if the early test is negative.
The soda is so sweet that some women find it nauseating. You might tolerate it better if you bring a lemon and squeeze a bit of lemon juice into the drink. This won’t affect test results.
If the GCT result is above a set cutoff value (usually 140 mg if the glucose is measured in the plasma portion of the blood), then a more accurate, but more difficult, diagnostic test is performed. An exception is the rare circumstance that the GCT is so high that giving more glucose would be dangerous.
The diagnostic test for gestational diabetes is called a glucose tolerance test (GTT) or oral glucose tolerance test (OGTT). In this test, 100 grams of gluocse are given to a woman to drink after she has fasted overnight for 8 to 14 hours. About 15 percent of women are estimated to have abnormal GCT values. Of these, about 15 percent are found to have gestational diabetes based on the GTT. The GTT is a 3-hour test, so you need to be prepared to spend the morning at your provider’s office or in the clinic or laboratory. Bring reading material!
Blood will be drawn four times during a GTT. The first time is before you drink the glucose solution. This is called a fasting blood sugar (FBS). Blood is then drawn at 1 hour, 2 hours, and 3 hours after you drink the sugar solution. The FBS value should be low, and glucose values should increase at 1 and 2 hours and then decrease at 3 hours, although not usually back to the fasting level. For each of these bloods, a cutoff value is set that indicates a high level of glucose. If a woman has two or more high values, she is considered to have gestational diabetes.
The first step in treatment for gestational diabetes is a special diet.
This diet is based on guidelines of the American Diabetic Association (ADA). All women with two or more abnormal values on the GTT will be given an ADA diet. Many times, women with only one abnormal value will be placed on the diet as a precautionary measure, especially if the high value was the FBS.
If you need to be placed on an ADA diet, you should meet with a dietitian, nutritionist, or nurse who specializes in the care of pregnant women with diabetes and is familiar with this diet and how to individualize it. The diet usually consists of 30 to 35 calories per kilogram of ideal body weight based on height. (A kilogram is 2.2 pounds.) The exact number of calories will depend on the time in pregnancy of diagnosis and your level of activity. The ADA diet gives you choices throughout the day from various food groups, so you can adjust it to meet your personal, family, and cultural eating patterns. In general, you will avoid a carbohydrate load-eating a lot of carbohydrates at one time, such as a large bagel. You will limit simple sugars or sweets.
If you are at risk for gestational diabetes, and your GCT is normal, it may be repeated at 34 weeks. The GCT may be repeated if the baby is growing larger than expected or if you develop pregnancy-induced hypertension. In one study, it was reported that 8 percent of previously negative GCTs become positive at 34 weeks gestation.
Women with diabetes will be taught to test their own blood sugar at home, usually several times a day, an hour after meals, and before eating in the morning. This determines whether the diet is working and whether there is a need for insulin. When the mother’s blood sugar is well controlled, the baby grows normally. The complications of birth sometimes seen with large babies will be avoided.
The fetuses of women with diabetes will be carefully monitored in the third trimester for signs of distress. Knowing the due date is important, as most experts advise avoiding a postdates delivery with diabetes. A sonogram usually will be performed at the time of diagnosis to verify gestational age if one had not been done previously. With care and attention, gestational diabetes will not adversely affect mother or baby.