What is gestational diabetes?

Gestational diabetes is a condition that can develop during pregnancy. It is a type of diabetes – a condition in which your body can’t control the amount of glucose (sugar) in the blood.

The word ‘gestational’ simply means ‘relating to pregnancy’.

Most women with gestational diabetes have healthy pregnancies and healthy babies. However, sometimes gestational diabetes can cause problems for both you and your baby, particularly if it is not identified and treated.

Gestational diabetes can be thought of as an ‘early warning’ indicator that the woman has a higher than usual risk for type 2 diabetes in later life.

Causes of gestational diabetes

To understand what gestational diabetes is, it can help to understand how your body uses glucose.

Your body needs some glucose in your blood to provide energy. The levels of blood glucose levels are kept at safe limits in your body, by a hormone called insulin. If your glucose level is too high, you may become unwell.

When your blood glucose level is high (such as after a meal), insulin allows the extra glucose to be stored in your cells for later use. Then, when your blood glucose levels fall, another hormone (glucagon) releases some of that stored glucose to keep enough energy available to your body.

When you are pregnant, your body produces high levels of hormones. Some of these hormones stop insulin working as well as it normally does. Usually, the body responds by increasing the amount of insulin it produces. However, some women do not produce enough of this extra insulin, resulting in gestational diabetes.

"My health was fine until about 26 weeks into my pregnancy. Then at a routine appointment they noticed glucose in my urine, so they said they needed to do a test to rule out gestational diabetes. They told me I had it and asked me to attend the diabetic clinic the following day."Gemma, mum of one

Risk factors for gestational diabetes

You are more likely to develop gestational diabetes if:

  • you had a body mass index (BMI) of more than 30 before you became pregnant
  • you have previously given birth to a baby weighing 4.5kg (around 10lb) or more (macrosomia)
  • you had gestational diabetes in a previous pregnancy
  • you have a parent, brother, sister or child with diabetes
  • your family are of black Caribbean, black African, South Asian or Middle Eastern origin.

Some women who develop gestational diabetes do not fall into any of these categories. They may have been tested for other reasons, such as glucose in the urine or if their baby seems large. As we find out more about gestational diabetes, more women from different risk categories are being tested. Being tested does not mean that you have it – just that you may be at higher risk.


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Last reviewed on March 1st, 2015. Next review date March 1st, 2018.

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