1-Hour Gestational Diabetes Test (O’Sullivan Testing)

1 Hour Gestational Diabetes Screen

Pregnant woman talking to her doctor about gestational diabetes and the O'Sullivan test she needs to takeThe O’Sullivan test measures pregnant women’s body’s reaction to glucose (sugar). The test is administered between the 26-28 week mark during the pregnancy and is done to screen for gestational diabetes.

Gestational diabetes is a condition when women without diabetes develop high blood sugar levels while they are pregnant.

After going through the test, that is further explained below, you will know if your levels are below normal, normal, or above normal. If your levels are abnormal, you will need to schedule additional tests to confirm your diagnosis.

The values that are used to determine gestational diabetes were first detected by O’Sullivan and Mahan in 1964 during a study designed to be able to recognize the risk of developing type 2 diabetes. Later the test was informally named after O’Sullivan.

Why am I Having This Test?

This test is being performed to screen for gestational diabetes, or elevated blood sugar levels during pregnancy. Having elevated blood sugar levels during pregnancy can affect your baby and delivery. Most pregnant women should have this test performed between 26-28 weeks. Some women have this test done more than once if they are considered to be high risk for having gestational diabetes or if the original test was performed prior to 24 weeks. Your physician will advise you as to what is recommended.

Will you be breastfeeding your baby? Prepare your body the best way you can with the right nutrition for your baby’s overall health. Learn more here…

How is This Test Done?

orange sugary drink that pregnant women drink before their o'sullivan test for diabetesYou will be given a drink containing glucose from your physician. This is usually given to you when you are around 24 weeks to drink prior to your 28-week appointment. It is recommended you put the drink in the refrigerator; it seems to taste better cold.

  • You are directed to drink the entire bottle within 5 minutes.
  • You will then need to have your blood drawn 1 hour after completing the drink.
  • It is recommended showing up to the lab at least 15 minutes prior to the 1-hour time limit, just in case there is a wait – lab will not draw you if you are over the 1-hour limit and you will have to do the drink again.
What Do I Do On The Day of The Test?

timer showing a 60 minute wait for taking the o'sullivan testingOn the day of testing, avoid foods or snacks that are high in sugar, otherwise, you should eat normally. Time your blood draw to complete the test prior to your physician appointment. Your blood needs to be drawn exactly 1 hour from completion of the glucola drink. Make sure you alert lab personnel that you are there for a timed diabetic test and the time you are due to be tested.

Looking for more helpful tips? Download your pregnancy planning kit, now!

What Do The Test Results Mean?

A normal or negative result means that you do not have gestational diabetes. An abnormal or positive result means that you are at risk for gestational diabetes and an additional test, called a 3-hour glucose tolerance test, will need to be performed. You will be given specific instructions should you need to have this test done.


women preventive health care Milwaukee

Contact Us

Phone: 262-544-4411
Fax: 262-650-3856

Moreland OB-GYN Associates, S.C. now offers nine locations to serve your needs. Visit us in Waukesha,
Mukwonago, Sussex, Brookfield, Hartland, Delafield, Oconomowoc Hostpital, Oconomowoc Physician Center & Watertown.

Baby Gallery

Submit your Moreland OB-GYN baby photo to be added to our Baby Gallery
Click To See Gallery

View Our Products

We understand the importance of women's sexual health and provide a safe, private environment. Click here to view products from Wisconsin's OB-GYN Specialists.