Gestational diabetes is a type of diabetes that only occurs during pregnancy. Despite the fact that developing gestational diabetes means an increased risk of developing diabetes mellitus later on in life, it will go away after the baby is born.
In diabetes, the body is unable to properly metabolize glucose (simple sugar). The levels of insulin in the blood actually increase during pregnancy, however the body becomes resistant to insulin’s effects. The reason for this is not entirely clear, but it may be due to pregnancy hormones: estrogen, progesterone, or human placental lactogen. The purpose of insulin resistance is most likely to ensure an adequate supply of glucose for the fetus.
Between 1 to 3 percent of pregnancies in the United States are affected by gestational diabetes. Women who are pregnant and have a family history of diabetes, are obese, or are age 30 or older are at greater risk for developing gestational diabetes. Other risk factors include a history of delivering very large babies or of having babies that were malformed or stillborn without an apparent cause. Glucose in the urine is a sign of gestational diabetes, but it is not a diagnosis.
Women who have gestational diabetes can control their glucose levels with the right treatments, and they don’t experience fetal death any more often than women who don’t have diabetes. The main problem seen in babies of women with gestational diabetes is macrosomia – they grow too large. Because they’re so big, these babies are more likely to be injured during birth, especially when their shoulders get stuck during delivery.
Although experts disagree on whether all women should be routinely screened for gestational diabetes, those who argue in favor of screening all women point out that as many as one-third to one half of women with gestational diabetes may be missed if only high-risk women are screened.
The screening test for gestational diabetes is called a glucose challenge test (GCT), or an oral glucose challenge test (OGCT). Women drink a sugar-sweetened beverage containing 50 grams of glucose. 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, the test may be performed earlier and repeated between 24 and 28 weeks of gestation.
Some women find soda too sweet and end up feeling nauseous because of it. If you’re one of those women, try squeezing some fresh lemon juice into your drink – it might help you tolerate the sweetness better without changing the test results.
If the GCT result is above the set cutoff value, this usually means that the person has diabetes. An exception to this rule would be if the GCT is so high that giving more glucose would be dangerous for the person.
The diagnostic test to screen for gestational diabetes is called a glucose tolerance test (GTT) or oral glucose tolerance test (OGTT).
In this test, 100 grams of glucose 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!
A glucose tolerance test (GTT) involves having your blood drawn four times. The first time is before you drink a sugar 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 blood draws, there is a cutoff value that indicates a high level of glucose. If a woman has two or more high values, she is considered to have gestational diabetes.
For gestational diabetes, the first line of treatment is always a special diet. This diet is based on the American Diabetic Association’s (ADA) guidelines. All women with two or more abnormal values on the glucose tolerance test (GTT) will be given an ADA diet. Many times, even women with only one abnormal value may be placed on the diet as a precaution, especially if the high value was for fasting blood sugar (FBS).
If you have been diagnosed with diabetes and need to be placed on an ADA diet, you should meet with a dietitian, nutritionist, or nurse who specializes in this type of care. The ADA 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 of diagnosis during pregnancy and your level of activity. ADA diet gives you the freedom to choose from a variety of food groups throughout the day, so you can easily tailor it to fit your personal, family, and cultural eating habits. You will mostly avoid eating a lot of carbohydrates at once – like, for example, a large bagel. You will also limit your intake of simple sugars and sweets.
The GCT test may need to be repeated during your pregnancy if you are at risk for gestational diabetes and your first test was normal. The test may also be repeated if the baby is growing larger than expected, or if you develop pregnancy-induced hypertension. According to one study, 8 percent of women who originally had negative GCT results became positive at 34 weeks gestation.
Women with diabetes who are pregnant will be taught how to test their own blood sugar at home, typically several times a day. This is done an hour after meals, and before eating in the morning, in order to determine if the diet is working and if there is a need for insulin. If the mother’s blood sugar is well controlled, then the baby will grow normally. However, if it isn’t well controlled, the baby might experience complications during birth.
The third trimester is a critical time for monitoring the fetuses of women with diabetes. It is important to know the due date, as most experts advise against postdates delivery in cases of diabetes. A sonogram will usually 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.