Causes of gestational diabetes

Researchers don't yet understand why some women get gestational diabetes and others don't. But we know that here are some risk factors that make it more likely and we have outlined these below. If you have one or more of these then you are more likely to get gestational diabetes but doctors do not yet know why. Although having a high BMI is a risk factor for gestational diabetes, slim women can also get it.

To understand what causes gestational diabetes, 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.

Read more about being tested for gestational diabetes