There are so many different lab tests in pregnancy that sometimes it’s hard to keep up.

Your friends might have described the glucose tolerance test in pregnancy as ‘that gross sugar drink test’.

Perhaps you know somebody who had an abnormal blood glucose test in pregnancy.

Here are 11 frequently asked questions about the blood glucose test, what blood glucose testing involves and why it’s done in pregnancy.

#1. What is a glucose test during pregnancy?

Having a blood glucose test in pregnancy helps to diagnose gestational diabetes mellitus (GDM).

There are several ways to test your blood glucose level and your body’s ability to break down sugar. Depending on where you live, the process of assessing risk factors and diagnosing GDM might differ.

Usually in the first trimester, your antenatal blood tests might include a test called HbA1C (also known as an A1C test).

If the result of the A1C test comes back as high, it indicates you’re at risk of developing GDM or another type of diabetes during pregnancy.

The A1C test can’t diagnose diabetes, so you’ll also be offered a glucose tolerance test for further screening and diagnosis.

These tests are usually done in two steps:

Glucose challenge test (GCT), sometimes called the 1 hour blood glucose test
Oral glucose tolerance test (GTT), also known as the 3 hour blood glucose test.

The GCT is becoming a standard antenatal test for all pregnancies. If it’s positive, you’ll be asked to follow up with a GTT to diagnose GDM.

In case you are wondering, read Bellybelly’s article Is Routine Testing For Gestational Diabetes Necessary?

#2. What is gestational diabetes mellitus?

Gestational diabetes mellitus, commonly referred to as GDM, occurs only during pregnancy when hormones prevent your pancreas from releasing sufficient insulin.

Insulin is a hormone that allows the cells to convert sugar in the blood into energy. Insulin resistance causes high blood sugar levels.

Usually women with GDM have healthy pregnancies and babies.

GDM, however, increases the risk of:

Macrosomia. This is when a baby grows larger than usual, causing problems during birth and increasing the chance of induction and c-section
Polyhydramnios, which meansbthere is too much amniotic fluid; this can lead to further complications in pregnancy
Premature birth
Pre-eclampsia, which is high blood pressure during pregnancy. This can lead to pregnancy complications, if not treated
A baby developing low blood glucose levels or jaundice after birth
Stillbirth, although this is rare.

Because of these factors, a glucose test is a standard pregnancy check up, done to make sure all is well with you and your baby.

#3. Who needs to have glucose tolerance testing in pregnancy?

All pregnant people are advised to be screened for their risk of GDM. Anyone is at risk of developing GDM but you’re at increased risk if:

Your BMI suggests ‘obese’
You have a family history of diabetes
There is a high HbA1C test result in your early antenatal blood work
You are aged over 35, and particularly if you are over 40
You had GDM in a previous pregnancy
You are having a multiple pregnancy with twins or triplets
You have polycystic ovary syndrome (PCOS)
You are of Aboriginal and Torres Strait Islander, Melanesian, Polynesian, Indian subcontinent, Middle Eastern or Asian background.

If you’re high risk, you can skip the GCT and go straight to diagnostic glucose tolerance testing.

#4. When should I have a glucose test?

Both the GCT and GTT are usually done between 24 and 28 weeks, unless there’s cause for concern earlier than this. If you miss this window, both diabetes tests can be done later in pregnancy.

#5. What should I eat before the glucose test?

You don’t need to do anything to prepare for a 1 hour glucose test (GCT). You should eat and drink normally beforehand so your body will have a normal reaction to the test.

You’ll be given a syrupy drink containing glucose and afterwards you need to wait at the lab for one hour before having your blood drawn.

The 3 hour glucose tolerance test is a fasting blood glucose test. Your care provider will ask you to fast overnight and on the morning of your glucose test. In some countries, you might be asked to eat 150 mg of carbohydrates per day for the three days before the fasting period begins.

When you arrive for your glucose testing you’ll have a blood test. This determines your fasting blood glucose, which means the amount of glucose in your blood without food being consumed.

You’ll then be given a syrupy drink with a higher level of glucose than the GCT. You’ll wait at the lab for two hours. You can’t walk around, or leave and come back, as exercising helps your body break down glucose and can affect the test results.

After two hours you’ll have a second blood test to determine your blood sugar levels in response to the glucose solution. In some countries, you’ll have a blood sample taken after one hour, and then again at two and three hours.

#6. Is the glucose tolerance test safe during pregnancy?

Yes. Blood glucose tests are very safe and are classed as standard tests in pregnancy. Some women, however, experience side effects, such as:

Nausea
Vomiting
Dizziness
Tiredness
Bloating and cramps
Headache.

There’s some evidence to show these side effects depend on the type of glucose used, so it’s important to discuss any concerns you have with your health care provider.

#7. How do I pass the glucose tolerance test in pregnancy?

By following the preparation guidelines you’ll have the most accurate results for your GTT. You should be eating intuitively and maintaining a balanced diet throughout pregnancy. This will help your test results be as accurate as possible.

In many countries, it’s recommended you pay specific attention to your diet in the three days prior to your GTT, and make sure you have a balance of proteins, fats and carbohydrates in each meal.

Read our article Healthy Breakfast – 13 Delicious And Healthy Breakfast Ideas to help keep your blood glucose levels stable.

#8. Does a high blood glucose level mean diabetes?

If you ‘fail’ the glucose test during pregnancy, it indicates your body isn’t able to use insulin effectively and you might have GDM.

Different countries have different glucose test guidelines; therefore, whether or not you’re diagnosed with GDM depends on where you live.

Your health care provider will contact you with your glucose test results within a few days. If you meet the diagnostic criteria for GDM in your area, you should be referred to a team of doctors, midwives and dieticians who specialise in gestational diabetes; they will manage your diabetes care.

If you are diagnosed with gestational diabetes in your pregnancy, you are at increased risk of developing type 2 diabetes later in life. In that case, you might require follow up diabetes care or screening after pregnancy.

#9. What can I do to manage the risks of diabetes in pregnancy?

It’s really overwhelming to get a diagnosis of gestational diabetes. You might do everything ‘right’ to keep yourself well in pregnancy and still receive a diagnosis of GDM.

Gestational diabetes isn’t necessarily a reflection on your health or weight, or the health of your baby. There’s still plenty you can control to support your health. Many pregnant people use diet to manage their blood sugar levels and don’t need medication.

Carbohydrates and gestational diabetes

There’s some evidence to suggest monitoring your carbohydrate intake in pregnancy is an effective way to control gestational diabetes without medication. The body turns carbohydrates into glucose within two hours of eating. That means your blood glucose levels are more easily affected by the carbohydrates you eat.

Most people who eat a standard Western diet consume too many simple or processed carbs and sugar. In recent years there’s been a focus on improving the quality of carbs in our diets. You might have heard of low carb or keto diets and wondered whether they might help prevent or manage high blood glucose levels.

Clinical trials on these diets and their effects on pregnancy are limited, due to ethics. What we do know is that eating a diet high in nutrition and reducing the amount of highly processed food has many positive benefits for your pregnancy and your growing baby.

You don’t have to think of it as a restrictive diet. Instead, focus on healthy and nutritious food sources.

If you’re in need of some inspiration read our article 10 Simple Diet Hacks For A Healthy Lifestyle.

#10. What else should I do to manage glucose tolerance in pregnancy?

If you’re diagnosed with gestational diabetes, you’ll be given a blood glucose meter so you can check your blood sugar levels at home.

Blood glucose monitoring involves a small prick to your finger and a test strip to monitor your levels before and after meals. It helps you and your care team make adjustments to your diet to keep your glucose levels stable.

The American Diabetes Association suggests the following targets for women who are testing their blood glucose levels during pregnancy:

Pre-meal: 95 mg/dl or less
One hour post meal: 140 mg/dl or less
Two hours post meal: 120 mg/dl or less.

You’ll also be offered regular ultrasound scans, to assess your baby’s growth and placenta function.

If you can’t stabilise your blood glucose level, you’ll be encouraged to consider medication, to help your body use insulin more effectively. If diet and other medications aren’t helping, your care team can discuss injectable insulin.

#11. Why do pregnancy glucose test results differ by country?

Different protocols for the diabetes test are used in different parts of the world. How the test is performed, what is considered a ‘normal blood glucose level’ and whether or not you’re diagnosed with GDM will depend on where you live. This information can help you make an informed decision about how to manage your diagnosis.

In most countries, the threshold for a fasting glucose level is between 5.1 and 5.8 mmol/L.

The threshold for glucose levels at the two hour mark, after 75 grams of glucose (the most common GTT glucose amount) is between 8.5 mmol/L and 11.1 mmol/L.