Tests and diagnosis

By Mayo Clinic Staff

Medical experts haven't established a single set of screening guidelines for gestational diabetes. 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.

When to screen

Your doctor will likely evaluate your risk factors for gestational diabetes early in your pregnancy.

  • If you're at high risk of gestational diabetes — for example, your body mass index (BMI) before pregnancy was 30 or higher or you have a mother, father, sibling or child with diabetes — your doctor may test for diabetes at your first prenatal visit.
  • If you're at average risk of gestational diabetes, you'll likely have a screening test for gestational diabetes sometime during your second trimester — between 24 and 28 weeks of pregnancy.

Routine screening for gestational diabetes

  • 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 tolerance testing. For the follow-up test, 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 have gestational diabetes, your doctor will likely recommend frequent checkups, especially during your last three months of pregnancy. During these exams, your doctor will carefully monitor your blood sugar. 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, or you need to take insulin, or you have other pregnancy complications, you may need additional tests to evaluate your baby's general health. These tests assess the function of the placenta, the organ that delivers oxygen and nutrients to your baby by connecting the baby's blood supply to yours. If your gestational diabetes is difficult to control, it may affect the placenta and endanger the delivery of oxygen and nutrients to the baby. Tests to monitor your baby's well-being include:

  • Nonstress test. Sensors are placed on your stomach and connected to a monitor to measure your baby's heart rate, which should increase when the baby moves. If your baby's heart doesn't beat faster during movement, the baby may not be getting enough oxygen.
  • Biophysical profile (BPP). This test combines a nonstress test with an ultrasound study of your baby. There's a scoring system that enables your doctor to evaluate your baby's heartbeat, movements, breathing and overall muscle tone, and determine whether your baby is surrounded by a normal amount of amniotic fluid. Your baby's scores on heartbeat, breathing and movement help your doctor tell if the baby's getting enough oxygen. When the amniotic fluid is low, it may mean that your baby hasn't been urinating enough. This 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 how often your baby kicks over a set time. Infrequent movement may mean your baby isn't getting enough oxygen.

Blood sugar testing after you give birth

Your doctor will check your blood sugar after delivery and again in six to 12 weeks to make sure that your level has returned to normal. If your tests are normal — and most are — you'll need to have your diabetes risk assessed at least every three years. If future tests indicate diabetes or prediabetes — a condition in which your blood sugar is higher than normal, but not high enough to be considered diabetes — talk with your doctor about increasing your prevention efforts or starting a diabetes management plan.

Mar. 24, 2011