Gestational diabetes mellitus (GDM) is a type of diabetes that can occur in the second part of the pregnancy and goes away once the baby is born. It is diagnosed when a woman has higher than normal blood glucose levels during pregnancy.
Some women with gestational diabetes may need no treatment, some need a strict diet and others may need insulin injections.
As GDM is a condition that occurs during pregnancy, it is not the same as having pre-existing diabetes during your pregnancy. Between 12% and 14% of pregnant women develop gestational diabetes, usually around week 24 to week 28 of pregnancy.
Typically, women with gestational diabetes have no symptoms. Most women are diagnosed after routine tests during pregnancy.
Some women with gestational diabetes (about 30%) have larger than average babies. As a result, they are more likely to have intervention in labour such as a caesarean birth. But the baby will not be born with diabetes.
Studies have suggested that women who develop gestational diabetes have a 50% increased risk of developing type 2 diabetes later in life. Their baby is also at greater risk of developing type 2 diabetes in later life.
Testing for gestational diabetes
All women are screened for gestational diabetes at their 24 to 28 week routine check-up. Women who are at higher risk may be tested more often. You are at higher risk of developing gestational diabetes if you:
- are above the healthy weight range or gaining too much weight in the first half of pregnancy
- over the age of 35 years
- have a family history of type 2 diabetes
- come from an Aboriginal and Torres Strait Islander or some Asian backgrounds
- have had gestational diabetes before
- have had polycystic ovary syndrome
- have had a large baby before
- are taking some types of anti-psychotic or steroid medications
Glucose tolerance test
The ‘glucose tolerance test’ is the diagnostic test used to find out if you have gestational diabetes. It requires fasting for 10 hours (generally overnight, missing breakfast). A blood test is taken, followed by a 75g glucose drink and further blood tests at 1 and 2 hours later. You will be required to remain at the laboratory for the 2-hour test.
Treatment for gestational diabetes
Most women diagnosed with gestational diabetes will have a healthy pregnancy, normal delivery and a healthy baby.
A healthy low-fat, low-sugar diet and regular exercise, such as walking or swimming, can help reduce blood sugar levels. You may be referred to an obstetrician and dietitian and may need more frequent antenatal appointments and regular monitoring of your blood sugar levels. If your blood sugar levels remain high despite changes to your diet and an exercise regime, you may need medication, usually in the form of insulin, to lower your blood sugar levels.
Learn more about how to manage gestational diabetes.
Labour and birth
If you have diabetes, it's strongly recommended that you give birth with the support of a consultant-led maternity team in a hospital.
Read more about where you can give birth, including in hospital.
Babies born to diabetic mothers are often larger than normal. This is because blood glucose passes directly from you to your baby, so if you have high blood glucose levels your baby will produce extra insulin to compensate. This can lead to your baby storing more fat and tissue. This in turn can lead to birth difficulties, which requires the expertise of a hospital team.
After the birth
Two to four hours after your baby is born, they will have a heel prick blood test to check whether their blood glucose level is too low. Feed your baby as soon as possible after the birth (within 30 minutes) to help keep your baby's blood glucose at a safe level.
If your baby's blood glucose can't be kept at a safe level, they may need extra care. Your baby may be given a drip to increase their blood glucose.
Read more about special care for babies.
If you had gestational diabetes, you can stop all treatment after the birth. You should be offered a test to check your blood glucose levels before you go home and at your 6-week postnatal check. You should also be given advice on diet and exercise.
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Last reviewed: August 2019