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Tests and diagnosis
By Mayo Clinic staffYour doctor will likely evaluate your risk factors for gestational diabetes early on in your pregnancy. Most women will have a screening test for gestational diabetes sometime during the second trimester of pregnancy.
Routine screening for gestational diabetes
Screening for gestational diabetes is recommended for most women. Medical experts haven't established a single set of screening guidelines. Some question whether gestational diabetes screening is needed if you're younger than 25 and have no risk factors. Others say that screening all pregnant women — no matter their age — is the best way to catch all cases of gestational diabetes.
Your doctor will recommend a screening schedule based on your specific risk factors. For most women with average risk of gestational diabetes, a blood test known as a glucose challenge test is recommended between weeks 24 and 28 of pregnancy. If you're at a high risk of gestational diabetes, your doctor may test you earlier.
- Initial glucose challenge test. You'll begin the glucose challenge test by drinking a syrupy glucose solution. One hour later, you'll have a blood test to measure your blood sugar level. A blood sugar level below 130 to 140 milligrams per deciliter (mg/dL), or 7.2 to 7.8 millimoles per liter (mmol/L), is usually considered normal on a glucose challenge test, although this may vary at specific clinics or labs. If your blood sugar level is higher than normal, it only means you have a higher risk of gestational diabetes. Your doctor will diagnose you after giving you a follow-up test.
- Follow-up glucose challenge tests. For the follow-up tests, you'll be asked to fast overnight and then have your fasting blood sugar level measured. Then you'll drink another sweet solution — this one containing a higher concentration of glucose — and your blood sugar level will be checked every hour for a period of three hours. If at least two of the blood sugar readings are higher than normal, you'll be diagnosed with gestational diabetes.
If you're diagnosed with gestational diabetes
If you're diagnosed with gestational diabetes, your doctor will likely recommend frequent checkups, especially during the last three months of pregnancy. During these exams, your doctor will carefully monitor your blood sugar level. Your doctor may also ask you to monitor your own blood sugar daily, as part of your treatment plan.
If you're having trouble controlling your blood sugar level, you need insulin, or you have other pregnancy complications, you may need additional tests to assess your baby's general health. These tests are designed to assess the function of the placenta. This is because if your gestational diabetes is difficult to control, it may affect the placenta and endanger the exchange of oxygen and nutrients to the baby. One abnormal test result doesn't necessarily indicate a problem. Your doctor may do additional tests to more accurately assess how your baby is doing.
- Nonstress test. Sensors placed on your stomach are connected to a monitor. This test evaluates increases in fetal heart rate that are expected with fetal movement. If they're absent, the fetus may not be receiving enough oxygen.
- Biophysical profile (BPP). This test combines a nonstress test with a fetal ultrasound. Your doctor assesses your baby's movements, breathing and whether a normal amount of amniotic fluid is present. The components assessing fetal activity indicate the baby's oxygen status at the time the test is done. Decreased fluid means your baby hasn't been urinating enough and could indicate that over time the placenta has not been working as well as it should.
- Fetal movement counting. You may perform this simple test at the same time as the nonstress test or the biophysical profile. You simply count the number of times your baby kicks within a certain time frame. Less movement may mean your baby isn't getting enough oxygen.
Blood sugar testing after you give birth
To make sure that your blood sugar level has returned to normal after your baby is born, your doctor will check your blood sugar levels after delivery and again in six weeks. If your test results are normal, it's a good idea to have your diabetes risk assessed at least every three years. If your blood sugar levels indicate diabetes or prediabetes — a condition in which your blood sugar level is higher than normal, but not high enough to be classified as diabetes — talk with your doctor about starting a diabetes treatment plan.
- Strehlow SL, et al. Diabetes mellitus & pregnancy. In: DeCherney AH, et al. Current Diagnosis & Treatment: Obstetrics & Gynecology. 10th ed. New York, N.Y.: McGraw-Hill; 2007. http://www.accessmedicine.com/content.aspx?aID=2385290. Accessed Jan. 9, 2009.
- Jovanovic L. Screening and diagnosis of gestational diabetes mellitus. http://www.uptodate.com/home/index.html. Accessed Jan. 5, 2009.
- Jovanovic L. Treatment and course of gestational diabetes mellitus. http://www.uptodate.com/home/index.html. Accessed Jan. 9, 2009.
- Diabetes. In: Cunningham FG, et al. Williams Obstetrics. 22nd ed. New York, N.Y.: McGraw-Hill; 2005:1172.
- Cheng YV, et al. Gestational weight gain and gestational diabetes mellitus. Obstetrics & Gynecology. 2008;112:1015.
- Gestational diabetes. American Diabetes Association. http://www.diabetes.org/gestational-diabetes.jsp. Accessed Jan. 6, 2009.
- Gilmartin AH, et al. Gestational diabetes mellitus. Reviews in Obstetrics & Gynecology. 2008;1:129. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=19015764. Accessed Jan. 3, 2009.
