Glucose Test During Pregnancy: Purpose, Types And Risks

check_icon Research-backed

Image: Shutterstock


Glucose test for pregnancy is an important test during pregnancy since the hormonal fluctuation and weight gain interrupt insulin’s function (contra-insulin effect). This, in turn, can increase blood sugar levels as a result of insulin resistance (1). In addition, persistent insulin resistance can lead to gestational diabetes, which can cause adverse outcomes for the mother and the baby (2).

The glucose screening test or glucose challenge test (GCT) is carried out between the 24th and 28th week of pregnancy to detect gestational diabetes (1). However, the test may be conducted earlier if a woman has risk factors for developing the disease (3).

This post will help you understand the glucose test in pregnancy, along with some tips to control blood sugar levels.

How Is Glucose Screening Test Done?

A glucose challenge test or glucose screening test is the first test that healthcare practitioners perform to screen women for gestational diabetes. Additional tests are required to confirm if a woman has gestational diabetes.

For the test, you don’t have to fast or do any preparation. Instead, you have to eat your normal diet and go to your doctor’s office, where (3)(4):

  • You need to drink a sweet liquid containing 50g of glucose.
  • After an hour, the doctor will take your blood sample and check your non-fasting sugar levels.

If your blood glucose levels are normal, it means you don’t have gestational diabetes. But, if your sugar level exceeds 200 mg/dL, you may have type 2 diabetes. On the other hand, if your blood glucose levels are greater than 140mg/dL (7.8 mmol/L), the doctor will advise you to take an oral glucose tolerance test.

Note: Talk to your healthcare provider to know if you need to skip any medicine which may affect your test results.

What Is An Oral Glucose Tolerance Test?

An oral glucose tolerance test (OGTT) measures your blood glucose levels before and after fasting. This test measures your body’s response to sugar and is done to confirm gestational diabetes. When a mother undergoes OGTT after glucose screening tests, it’s called the two-step test (5).

Two-step test

In the two-step test, a pregnant woman first undergoes the glucose challenge test. Then, if the test results show higher than normal blood sugar levels, she will be given an OGT test.

For OGTT, you will have to fast for at least eight to 14 hours before the test. You can, though, sip some water whenever you feel thirsty. Then, the doctor will take your blood sample to determine your fasting blood sugar levels. After taking the sample,

  1. You need to drink a sweet solution containing 100g of glucose.
  1. After that, the doctor will take another blood sample to evaluate your non-fasting sugar level every hour for three hours.

Any two or more readings (fasting, 1 hour, 2 hours, or 3 hours) higher than normal indicate you may have gestational diabetes. Here’s what the three-hour-OGTT results mean (4).

MealtimeTarget Sugar Levels (mg/dL)
Fasting95 mg/dL (5.3 mmol/L)
After 1 hour180 mg/dL (10.0 mmol/L)
After 2 hour155 mg/dL (8.6 mmol/L)
After 3 hour140 mg/dL (7.8 mmol/L)

Source: Mount Sinai 

In some cases, especially those where the mother has known risks for developing gestational diabetes, the doctor may order one-step glucose testing.

One-step test

For this test, your healthcare provider will take your blood sample to check your fasting blood sugar levels. Then, the doctor will

  1. Ask you to drink a sweet solution containing 75g of glucose.
  1. After that, the doctor will take another blood sample to evaluate your non-fasting sugar level two after every 60 minutes.

Like the two-step test, you will have to fast for at least 8 to 14 hours before this test. Here’s what the two-hour-OGTT results mean (4).

MealtimeTarget Sugar Levels (mg/dL)
Fasting92 mg/dL (5.1 mmol/L)
After 1 hour180 mg/dL (10.0 mmol/L)
After 2 hour153 mg/dL (8.5 mmol/L)

Source: Mount Sinai 

More than one higher than normal reading indicates you have gestational diabetes.

What Are The Risks Associated With Glucose Testing In Pregnancy?

Most pregnant women don’t experience any issues during or after glucose testing. However, as glucose testing requires a woman to fast and then drink a sugary solution, some women might experience mild side effects, such as (5)

  • Nausea
  • Sweating

In rare cases, drawing blood samples might increase the risk of other side effects, such as:

  • Light-headedness or fainting
  • Excessive bleeding
  • Multiple punctures to locate veins
  • Infection due to puncturing of the skin
  • Build up of blood under the skin (hematoma)

Do You Need To Take A Urine Test In Pregnancy?

Generally, urine has little or no sugar during pregnancy. However, when your blood sugar levels are too high, the body flushes excess glucose out of the body via urine. It means if a woman has high glucose levels in the urine (glucosuria), she may have gestational diabetes.

According to experts, about 50 percent of women have glucose in their urine at some time during pregnancy (6). Hence, your doctor will take your urine sample at every prenatal visit to check if the urine has glucose.

If your urine tests positive for glucose, your doctor may order a glucose screening test earlier than usual. It’s done to ascertain that high glucose levels in urine aren’t due to high sugar food or beverage intake before the test.

Note: Whether your urine tests positive for high sugar levels or not, you will be screened for gestational diabetes between the 24th and 28th weeks of pregnancy.

How To Lower Your Blood Glucose Level?

You have gestational diabetes, your single blood reading is abnormal, or you have normal sugar levels, monitoring and controlling sugar levels is vital for your and your baby’s long-term health. Here are some simple habits you can adopt and follow diligently.

  1. Consult a nutritionist. A nutrition expert will help you know how much weight gain is healthy for you and what you can do to ensure your weight stays within limits. They will also help you select the right type of foods and the right way to prepare meals so that you and your baby get all the nutrients you need.
  1. Eat a well-balanced diet with high-fiber foods, such as whole grains, and avoid refined grain intake as much as possible. It will help you maintain a healthy weight which is essential to combat insulin resistance, the main cause of gestational diabetes.
  1. Abstain from fruit juices. Instead, consume plenty of fresh, whole fruits and vegetables. Fruit juices are high in free sugar and often lack fiber, whereas whole fruits offer you all the nutrients, including fiber, that help keep your blood sugar levels in control.
  1. Consume three main meals and two to three snacks every day to fight cravings and hunger pangs. When you eat small amounts of food at frequent intervals of 2.5 to 3 hours, your blood sugar levels don’t spike.
  1. Fight cravings the healthy way. For instance, if you crave sweets, eat a handful of dried fruits, such as dates and figs. Alternatively, you can be a little creative and prepare a customized smoothie using fresh fruits, nuts, seeds, and milk.
  1. Indulge in some physical activity daily to keep yourself fit and flexible. For most women, combining different activities proves helpful in maintaining weight and preparing for smooth delivery. For instance, most women walk and do Kegel exercises. While walking (aerobic activity) keeps your sugar levels in control, Kegel (floor exercise) strengthens your pelvic muscles and prepares your body for labor.

Besides these, stay hydrated and sleep sound for at least eight to nine hours daily. Additionally, stay happy and stress-free so that your body can pass through all the changes in pregnancy smoothly.

Frequently Asked Questions

1. What should I not eat before my glucose test?

If participating in the OGTT test, you will be asked not to eat anything a few hours before it. However, you can drink water. On the other hand, you need not fast for a glucose challenge test. But it is advisable to not consume food items with high sugar content before the test (7).

2. Can I refuse the glucose test when pregnant?

Yes, if you are uncomfortable, you may refuse to take a glucose test when pregnant. However, considering the complications of unregulated diabetes on the mother and fetus, taking a glucose test during pregnancy is highly recommended. Consult your medical advisor to clarify your queries regarding the test.

3. Will a glucose test hurt my baby?

The glucose test is simple and does not harm your baby. Nonetheless, since the OGTT requires the extraction of a blood sample, unhygienic blood sampling could increase the risk of infections. Hence, ensure to take the test in a trusted lab that follows safety protocols (4) (8).

Glucose testing in pregnancy is crucial to monitor your sugar levels. Pregnant women undergo glucose screening tests between the 24th and 28th weeks to check for gestational diabetes. However, if you have high urine glucose levels or known risk factors for gestational diabetes, your healthcare professional will likely schedule your glucose screening test earlier than usual. In any case, monitor your sugar levels closely and follow healthy diet and lifestyle practices to keep sugar levels in control.

Key Pointers

  • Pregnant women may drink a sweet liquid of 50g of glucose to check for their sugar levels.
  • An oral glucose tolerance test (OGTT) is used to measure blood glucose levels before and after fasting.
  • Pregnant women may experience mild side effects such as dizziness, nausea, or sweating after drinking the sugary solution.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
The following two tabs change content below.

Dr. Mona Hardas

Dr. Mona Hardas is a practicing Ob/Gyn from Flint, Michigan, with over 20 years of experience in private practice. She is also actively involved in teaching medical students and residents as an associate clinical professor from MSU College of Human Medicine.  Dr. Hardas is interested in minimally invasive gynecology procedures, including laparoscopic hysterectomy, myomectomy, removal of adnexal masses, etc. Having... more

Swati Patwal

Swati Patwal is a clinical nutritionist and toddler mom with over eight years of experience in diverse fields of nutrition. She started her career as a CSR project coordinator for a healthy eating and active lifestyle project catering to school children. Then she worked as a nutrition faculty and clinical nutrition coach in different organizations. Her interest in scientific writing... more