Gestational diabetes, or GDM, occurs because pregnancy hormones increase resistance to the hormone insulin. Because insulin does not work as well during pregnancy, the pancreas must produce more of it to keep up with the body’s demand. For many pregnant women, this is not a problem. However, in some women, the pancreas is unable to produce as much insulin as the body needs to keep blood sugars in the normal range. As a result, blood sugar levels rise (hyperglycemia) and gestational diabetes may develop.
It is important to diagnose and treat GDM as it can have serious short- and long-term health consequences for both you and your baby. Don’t worry needlessly, however, if you have been told you have gestational diabetes. There are a lot of things you and your doctor and/or health team can do to keep you and your baby healthy both during the pregnancy and afterwards.
Gestational diabetes is common
GDM occurs in about 4-7% of pregnancies in the United States. It is one of the most common health problems in pregnancy. The incidence appears to be increasing as well, most likely due to the increase in the prevalence of overweight and obesity.
You are at high risk for GDM if you have any of the following:
- Obesity (BMI over 30)
- Prior history of gestational diabetes
- Strong family history of diabetes
These are all reasons to have early screening for gestational diabetes. Some health professionals will also screen early if you have any of the following:
- You test positive for glucose in your urine at a prenatal visit
- You have given birth to a big baby (9 pounds or greater)
- You have had an unexplained stillbirth
- You have had a baby with a birth defect
- You have high blood pressure
Because many women who develop GDM do not have any of these risk factors, most practitioners screen all pregnant women for GDM at 24 to 28 weeks of pregnancy.
I am healthy. Do I really need to have this screening test?
Some practitioners will not screen for GDM if the woman is at very low risk. To fall into this category, you must meet all of the following:
- You are younger than 25
- Your weight is in a healthy range
- You are not a member of a racial or ethnic group that has a high prevalence of diabetes, such as Native American, African American, Latino, Asian American, Pacific Islander
- None of your close relatives have diabetes
- You have never had a high blood sugar on testing
- You have never had a baby over 9 pounds or any other pregnancy complication that is associated with gestational diabetes
Only a small percentage of pregnant women will meet all of these criteria. Therefore, most obstetricians/gynecologists prefer to screen all pregnant women for GDM because the consequences of missing the diagnosis are serious.
Testing for GDM
In the United States, most OB-GYNs and family physicians caring for pregnant women prefer to use a 50-gram, 1-hour “glucose challenge test” as the initial screening test. The test is administered between the 24th and 28th week of pregnancy. This test involves drinking a standardized 50-gram load of glucose dissolved in water. If the test is positive, you will be asked to come back for a longer, but more definitive test as described below. Two different cut-off values for a positive test have been proposed: 130 mg/dL and 140 mg/dL. Ninety percent of pregnant women with GDM will have one-hour plasma glucose values that exceed 130 mg/dL. However, 20-25% twenty-five percent of pregnant women will have a positive screening test with this cut-off. Many of these women will fail to meet the criteria for GDM once they have the more definitive test (this is known as a “false positive” test).
The “gold standard” test for gestational diabetes in the U.S. is the 100 gram, 3-hour oral glucose tolerance test. You will drink a standardized 100-gram load of glucose dissolved in water. Blood is drawn before you drink the glucose and hourly for the next 3 hours. Criteria for diagnosing GDM are as follows:
- Fasting plasma glucose 95 mg/dl or higher
- 1-hour plasma glucose 180 mg/dl or higher
- 2-hour plasma glucose 155 mg/dl or higher
- 3-hour plasma glucose 140 mg or higher
Two or more of the plasma glucose levels listed above must be met or exceeded to make the diagnosis of gestational diabetes. The test should be done in the morning after an overnight fast of 8-14 hours and after at least 3 days of unrestricted diet (150 grams or more of carbohydrate per day) and unlimited physical activity. You should remain seated during the test. Also, you should not smoke during the test, but you should not smoke at all during your pregnancy, in fact, you should not smoke at all.
Outside of the United States, many clinicians follow the screening approach recommended by the World Health Organization: A 75 gram, 2-hour glucose tolerance test used as a one-step screening and diagnostic test. The test is considered positive if the fasting plasma glucose is 126 mg/dL and/or the 2-hour test is 140 mg/dL or higher.
In medicine, whenever there is disagreement about what is the best test or the best way of interpreting a test, it means that we don’t really know which approach is optimal. You should follow the recommendations of your clinician.
If I have it once, will I get it again?
A woman who had gestational diabetes in one pregnancy has a 43% chance that it will recur with the next pregnancy. Lifestyle changes, such as weight loss, improved nutrition, and regular exercise should be initiated in all women with a history of GDM before they conceive again. Prior to conception, fasting blood glucose and Hemoglobin A1c testing (a test of glucose levels over the previous 2-3 months) should be obtained. If they are abnormal, every effort should be made to get your glucose levels in good control prior to becoming pregnant again.
Does GDM harm my baby?
Poorly controlled gestational diabetes can lead to serious consequences for your baby. When your glucose levels are high, too much glucose can end up in your baby’s blood. Your baby’s pancreas will need to produce more insulin in order process this extra glucose. The excess insulin can cause your baby to get fat, particularly in the upper part of the body. When a baby is bigger than normal, we say the baby has macrosomia (macro=big, somia=body). Macrosomic babies may not pass easily through the birth canal, causing difficult deliveries, complications such as shoulder damage during delivery (shoulder dystocia), nerve damage, or even a fractured bone. If your health provider suspects you are going to have a macrosomic baby, she will probably recommend you have a cesarean section.
After delivery, the baby is at risk for developing low blood sugar (hypoglycemia) because of the extra insulin baby’s pancreas is producing. The baby’s blood sugar will be tested right after delivery. If it is low, you will be encouraged to feed him/her as soon as possible. If it is extremely low, the baby may require an intravenous (IV) glucose solution. Other complications for babies born to mom’s with uncontrolled gestational diabetes include jaundice (yellowing of the skin), low blood calcium, and high red blood cell counts. If control was especially poor, the baby’s heart function could be affected. Women with severe gestational diabetes have an increased risk of having a stillbirth in the last two months of pregnancy. Finally, babies born to women with GDM may be at increased risk for obesity and type 2 diabetes later in life.
What can I do to prevent any harm to my baby?
Luckily, there are a lot of things you can do to keep gestational diabetes in good control while you are pregnant. You will need to monitor your glucose using a home glucose meter (glucometer) and blood glucose testing strips. And, you will need to watch your diet. Many experts recommend you get nutritional counseling from a registered dietician so that you can develop specific meal and snack plans tailored to your height, weight, activity level, and food preferences. Regular exercise also helps because it increases sensitivity to insulin. In some cases, you will need to take insulin shots to keep your glucoses in the normal range, as recommended by your doctor. Most women with gestational diabetes who keep their glucose in good control will go on to deliver a healthy baby.
Do I need to do anything special after I deliver the baby?
The American Diabetes Association suggests that you should have your glycemic status checked about 6 weeks after delivery. Two tests are commonly used to test for postpartum glucose problems. One test is the fasting plasma glucose (blood is drawn in a laboratory after an overnight fast or no caloric intake for at least 8 hours). The other test is a 2-hour oral glucose tolerance test (GTT) that checks glucose levels 2 hours after you drink a standardized glucose drink (75 grams of anhydrous glucose dissolved in water). If the fasting plasma glucose is above 100 mg/dl but below 126 mg/dl, you have impaired fasting glucose. If it is 126 mg/dl or higher on two different blood tests, you have type 2 diabetes. If the 2-hour plasma glucose is between 140 and 199 mg/dl, you have impaired glucose tolerance. If it is 200 mg/dl or higher, you have type 2 diabetes.
If, at the 6-week postpartum visit, you find out you have impaired fasting glucose or impaired glucose tolerance, you should have your glycemic status checked every year. If glucose levels are normal at the 6-week visit, you should be retested at least every 3 years.
Are there any long-term effects of GDM?
Women who develop gestational diabetes have an increased risk of developing type 2 diabetes at some time in their lives. Overall, the risk is increased about 63%. However, if you have more than one pregnancy with GDM, your risk increases. It approaches 100% if you have had three pregnancies with GDM.
Certain indicators are associated with an increase in the risk of developing type 2 diabetes within 5 years of a GDM pregnancy, including the following:
- Development of GDM before the 24th week of pregnancy
- Plasma glucose levels remaining at the high end of normal or frankly elevated postpartum
- Impaired glucose tolerance (abnormal glucose tolerance test)
- Family history of diabetes
It is important to have regular follow-up, for the rest of your life, to assess whether you have developed prediabetes or diabetes or linked conditions, including high blood pressure and abnormal lipids. All women with a history of GDM should maintain a healthy weight and follow a regular program of physical activity.
If I want more information on gestational diabetes, where should I go?
The American Diabetes Association is an excellent source for information about gestational diabetes (www.diabetes.org/gestational-diabetes.jsp). You can obtain a copy of “Gestational Diabetes: What to Expect” via a hyperlink on the ADA gestational diabetes website. Other books available online or at your local bookstore include the following: