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What Is an Oral Glucose Tolerance Test? Why Do Pregnant Women Need To Take It?

Medically reviewed by Mitchie Gonzales-Montalbo, MD · Dietetics and Nutrition

Written by Fiel Tugade · Updated Sep 22, 2022

What Is an Oral Glucose Tolerance Test? Why Do Pregnant Women Need To Take It?

You experience different body changes as you go through your pregnancy journey. During your regular check-ups, your doctor may have mentioned something about having an OGTT. But what is this test all about? Is it necessary? Why do pregnant women need to get this test? Find out here. 

What Is an OGTT?

An oral glucose tolerance test, or OGTT, assesses a person’s ability to utilize sugar (glucose) intake. 

Doctors administer this test to measure the glucose levels before and two hours after drinking a special sweet drink. 

The OGTT is routinely done to pregnant women at 24-28 weeks age of gestation, and earlier for those at high risk for developing diabetes during pregnancy or gestational diabetes.

Gestational diabetes can be diagnosed if the sugar levels has reached 153 mg/dL or more, after 2 hours of 75-g OGTT.

How Can Gestational Diabetes Affect Your Pregnancy?

The majority of pregnant women have normal pregnancies and healthy babies. But at times, gestational diabetes may develop, especially if a woman has risk factors such as a familial history of diabetes. For most patients, blood glucose levels may return back to a normal range after giving birth. If you develop gestational diabetes, it is important to monitor your condition as it may result in complications such as the following:

  • Your baby may grow larger than usual, which can cause complications during labor. A large baby increases the likelihood of induced labor or a cesarean section. 
  • Polyhydramnios or having too much amniotic fluid
  • Premature birth
  • Pre-eclampsia , a state in pregnancy of having high blood pressure, swelling of the hands and feet, and other signs that may indicate organ damage
  • Stillbirth

After birth, your baby may develop low blood sugar or jaundice, which may demand hospitalization. And while gestational diabetes resolves after giving birth, you are also more likely to develop type 2 diabetes in later years.

The American College of Obstetricians and Gynecologists recommends screening for gestational diabetes in low-risk pregnant women between 24 and 28 weeks of pregnancy. This is because it is during these stages when gestational diabetes is most likely to develop.

Your doctor may advise you to have an earlier OGTT if you are at a higher risk of developing gestational diabetes. Among the risk factors are:

If you have one or more of these risk factors, then the doctor may endorse the test to you. 

How Can You Prepare for an OGTT?

Before the screening occurs, it is important that you inform your doctor about any medicine you are taking. There may be instances wherein you need to discontinue the use of certain medications for the time being. 

For at least 8 hours before your first blood sample, you should not eat, drink, smoke, or engage in strenuous exercise. Some people refer to this as fasting before the procedure.  

How Is the OGTT Done?

  • Like any other blood test, a medical representative will draw some blood samples for evaluation. The first sample shows the level of glucose in your blood after fasting. 
  • After your blood is taken, you will need to consume a small cup of very sweet liquid containing 50, 75, or 100 grams of glucose. 
  • As the test goes on, more samples may be taken over the next 1-3 hours, depending on the type of test. 
  • Because activity can influence test results, you will need to sit quietly for the whole duration of the test. You should also not consume anything during the test.

When all is done, your doctor will notify you when the results are available for viewing.

Key Takeaway

An oral glucose tolerance test, or OGTT, is a great way to determine whether or not you have diabetes that could possibly affect your pregnancy. You should not be afraid if your doctor suggests that you should have one as it is important in ensuring a safe and healthy pregnancy. 

Learn more about Diabetes Complications here. 


Hello Health Group does not provide medical advice, diagnosis or treatment.

Medically reviewed by

Mitchie Gonzales-Montalbo, MD

Dietetics and Nutrition

Written by Fiel Tugade · Updated Sep 22, 2022

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