The 1-hour gestational diabetes screen, or the O’Sullivan test, is a standard test performed between 24 and 28 weeks of pregnancy to assess how your body processes glucose (sugar). This test helps identify if you are at risk for gestational diabetes, a condition that causes elevated blood sugar levels during pregnancy.
Below, we explain why it's important to detect gestational diabetes, what to expect during your one-hour screen, and what your results mean. If your levels are abnormal, you will need to schedule an additional 3-hour glucose tolerance test to confirm your diagnosis.
This test is being performed to screen for gestational diabetes or elevated blood sugar levels during pregnancy. Elevated blood sugar levels during pregnancy can affect your baby and its delivery.
Most pregnant women should have this test performed between 24-28 weeks. If you are at high risk of developing gestational diabetes, your doctor may recommend earlier screening before the 24-week mark. High-risk factors include:
While some women may be predisposed to gestational diabetes, it’s important to remember that any woman can develop it, regardless of her health history or lifestyle. The exact cause of gestational diabetes is not fully understood, but it’s believed to be related to hormonal changes during pregnancy. The placenta produces hormones that help the baby develop but can also make it harder for the body to use insulin effectively. This condition, called insulin resistance, causes blood sugar levels to rise, leading to gestational diabetes.
By identifying and managing gestational diabetes early, you can help reduce potential risks for both you and your baby, such as excessive birth weight, preterm delivery, and complications during birth.
The 1-hour gestational diabetes screening is usually done around your 24-week prenatal visit. During the test, you’ll drink a glucose solution in the lab and must finish it within five minutes. Afterward, you’ll need to stay in the clinic or lab for exactly one hour. A technician will draw a blood sample at the one-hour mark to measure how your body processes glucose.
Physician tip: Bring a book, podcast, or something to keep you occupied during the 1-hour wait!
To prepare for a 1-hour gestational diabetes screening, follow these tips:
Always check with your healthcare provider for any specific instructions they may have.
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.
***Note: If you have an abnormal result, it does not necessarily mean you have gestational diabetes. This means that you should have further testing, such as a 3-hour glucose tolerance test, which provides a more detailed assessment of how your body processes sugar.
Looking for more pregnancy tips and guidance? Download our free Pregnancy Planning Kit and explore our additional resources below!
