Oral glucose tolerance test in pregnancy

Sometimes diabetes develops during pregnancy in women without diabetes, this condition is called gestational diabetes mellitus (GDM). Gestational diabetes is not caused by decreased insulin hormone level, it is caused by the hormones which are produced during pregnancy to support and develop the baby. These pregnancy hormones block the insulin effect in mother’s body, this is called insulin resistance. Insulin hormone can’t affect properly because of this pregnancy hormone-effect and can’t reduce blood sugar level as expected.  As a result, pregnant develops intolerance to carbohydrates and blood glucose level increases.

Oral glucose tolerance test (OGTT) is one of the blood test that is used to diagnose gestational diabetes. OGTT may be done between 24-28 weeks of the pregnancy.

Oral glucose tolerance test (OGTT) procedure in pregnancyglucose tolerance test

  • You don’t need to fast before first step OGTT also no other preparation is needed before the test,
  • First you’ll drink a liquid that contains 50 grams of sugar ( glucose)
  • Your blood will be drawn in a test tube after 1 hour
  • If the blood sugar level is lower than 140 mg/dL, result is accepted as normal
  • If the blood sugar level is higher than 140 mg/dL you will be requested to have the seconds step of the test
  • In second step of oral glucose tolerance test you’ll need to fast for 12 hours before the test
  • You will drink a liquid again and this time there will be 100 grams of sugar (glucose) inside
  • In seconds step your blood is collected after fasting before drinking glucose and then 1st , 2 nd and 3rd hours blood sample will be collected.

How the oral glucose tolerance test is performed ?

  • You will have blood drawn for  oral glucose tolerance test same as other blood tests but 4 times of blood collection is needed
  • First blood collection will be after fasting period at morning, this is for fasting blood sugar level
  • Then you’ll drink a liquid that contains 100 grams of sugar ( glucose)
  • Your blood will be drawn again for 3 times in every 60 minutes

Blood collection process

Your health professional ( nurse, technician, doctor, phlebotomist) will;

  • Wrap an elastic band around your upper arm
  • Clean the skin inside of your elbow or on the back of your hand with an antiseptic
  • Insert a needle in a suitable vein (you may feel a little a pain for a few seconds)
  • Place the tube and collect blood
  • Remove the needle and elastic band
  • Put a piece of cotton or bandage over the site

All blood collection process takes 1-2 minutes at most

Oral glucose tolerance test normal results

Normal results are expected as listed below to say that you don’t have gestational diabetes, you’ll be diagnosed for gestational diabetes at least 2 of these results are found abnormal

  • Fasting blood sample: Less than 95 mg/dL
  • 1st hour blood sample: Less than 180 mg/dL
  • 2nd hour blood sample: Less than 155 mg/dL
  • 3rd hour blood sample: Less than 140 mg/dL


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