There are so many different tests in pregnancy that sometimes it’s hard to keep up.
Your friends might have told you about the glucose test in pregnancy as “that gross sugar drink test”.
Perhaps you know somebody who had an abnormal glucose test in pregnancy.
Here are 11 frequently asked questions about the glucose test, what glucose testing involves, and why it’s done in pregnancy.
#1: What is a glucose test during pregnancy?
Having a glucose test in pregnancy helps to diagnose gestational diabetes mellitus (GDM).
There are several ways to test glucose levels 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 one called HbA1C.
If the result of HbA1C comes back as high, it indicates you’re at risk of developing GDM or another type of diabetes during pregnancy.
HbA1c can’t diagnose GDM, so you’ll also need glucose tolerance testing for further screening and diagnosis.
These screens are usually done in two steps:
- Glucose challenge test (GCT), sometimes called the 1 hour glucose test.
- Glucose tolerance test (GTT), also known as the 3 hour 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.
#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 levels of sugar to remain in the blood.
Usually women with GDM have healthy pregnancies and babies. But GDM increases the risk of:
- Macrosomia: a baby grows larger than usual, causing problems during birth and increasing the chance of induction and c-section
- Polyhydramnios: too much amniotic fluid, causing premature labour
- Premature birth
- Pre-eclampsia: high blood pressure during pregnancy, which can lead to pregnancy complications if not treated
- A baby developing low blood sugar or jaundice after birth
- Stillbirth, although this is rare.
Because of these factors, a glucose test is a standard pregnancy check up, 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 is 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 ovarian syndrome
- 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 glucose challenge test and go straight to diagnostic glucose tolerance testing.
#4: When should I have a glucose test?
Both the GCT and GTT should be done between 24-28 weeks. Either glucose test can be done later in pregnancy, however, if you miss this window.
#5: How do I prepare for the glucose test?
What to eat before a 1 hour glucose test in pregnancy (GCT)?
You don’t need to do anything to prepare for a GCT. You should eat and drink normally beforehand so your body has a normal reaction to the glucose test.
You’ll be given a syrup-like drink containing glucose and afterwards you need to wait at the lab for one hour before having your blood tested.
What to eat before a 3 hour glucose tolerance test (GTT)?
Before your GTT 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 150mg carbohydrates per day for the three days before the fasting period begins.
When you arrive for your glucose test you’ll have blood taken. This determines your fasting glucose, which means the amount of glucose in your blood without food being consumed.
You’ll then be given a syrup-like 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 change the test results.
After two hours you’ll have a second blood test to determine your blood glucose levels in response to the glucose solution. In some countries you have a blood test after one hour, and then a further blood test at two and three hours.
#6: Is the glucose tolerance test safe during pregnancy?
Yes. The glucose test is a very safe and standard test in pregnancy. Some women, however, experience side effects, such as:
- Bloating and cramps
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 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 have a balanced diet throughout pregnancy. This will help your glucose 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.
Here are some great examples of healthy, balanced breakfast ideas to help keep blood glucose levels stable.
#8: What does it mean if I fail the glucose test during pregnancy?
If you ‘fail’ the glucose test during pregnancy, it indicates your body isn’t able to use insulin effectively and you might have GDM.
Because different countries have different glucose test guidelines, whether or not you’re diagnosed with GDM depends on where you live.
Your 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.
#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 diabetes and don’t need medication.
Carbohydrates and gestational diabetes
There’s some evidence 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. This means your blood sugar levels are more easily affected by the carbohydrates you eat.
Most people eating a standard Western diet eat far too many simple or processed carbs and sugar. In recent years there has 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 gestational diabetes.
Research on these diets and their effects on pregnancy is limited, due to ethics. What we do know is that eating a diet high in nutrition and reducing highly processed foods has many positive benefits for your pregnancy and growing baby.
You don’t have to think of it as a restrictive diet. Instead, focus on healthy and nutritious food sources.
Carbohydrates come in many forms. Some are ‘simple’ like white bread, crisps, candy and fruit juice. Others are ‘complex’ such as whole grains, oats, brown rice and quinoa. Vegetables and legumes are unprocessed and whole food carbohydrates, and contain an array of important nutrients.
Fat are an important part of your diet, as your baby’s brain needs plenty for growth and development. Again, focus on healthy fats and avoid potato crisps and processed foods high in trans fats.
Protein foods should also be high quality; try to avoid processed meats.
Examples of healthy lower carb foods:
- Rye or sourdough toast with avocado and poached egg
- Chicken stir fry with plenty of colourful vegetables
- Cheese and seedy crackers.
Carbohydrates should be paired with a protein and fat to help with absorption of the glucose that carbohydrates produce.
Your care team will support you in making healthy food choices to manage gestational diabetes.
#10: What else should I do to manage glucose tolerance in pregnancy?
If you’re diagnosed with gestational diabetes you’ll be given a self-testing kit to monitor your blood sugar levels at home.
The glucose test involves a small prick to your finger before and after meals. It helps you and your care team make adjustments to your diet to keep your glucose levels stable.
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 levels, you’ll be encouraged to consider medication, to help your body use insulin more effectively. If diet and other medication aren’t helping, your care team can discuss injectable insulin.
#11: Why do pregnancy glucose test results differ by country?
Different protocols for the glucose test are used in different parts of the world. How the glucose test is done and whether you’re diagnosed with GDM depends 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 5.8mmol/L.
The threshold for glucose levels at the two hour mark, after 75 grams of glucose (the most common GTT glucose amount), is between 8.5mmol/L and 11.1mmol/L.