Causes of gestational diabetes  

Diabetes is caused by too much glucose (sugar) in the blood.

The amount of glucose in the blood is controlled by a hormone called insulin, which is produced by the pancreas (a gland behind the stomach).

Diabetes is caused either by insufficient insulin being produced, or the body becoming resistant to insulin, which means the insulin doesn't work properly.


When you eat, your digestive system breaks down food and the nutrients are absorbed into your bloodstream.

The hormone insulin is produced and acts like a key, opening the cells to allow glucose to move into the body for energy.

Gestational diabetes

During pregnancy, your body produces a number of hormones (chemicals), such as oestrogen, progesterone and human placental lactogen (HPL). These hormones make your body insulin-resistant, which means your cells respond less well to insulin and the level of glucose in your blood remains high.

The purpose of this hormonal effect is to allow the extra glucose and nutrients in your blood to pass to the foetus (unborn baby), so it can grow.

To cope with the increased amount of glucose in your blood, your body should produce more insulin. However, some women either cannot produce enough insulin in pregnancy to transport the glucose into the cells, or their body cells are more resistant to insulin. This is known as gestational diabetes.

Risk factors

You may be at increased risk of gestational diabetes if:

  • your body mass index (BMI) is 30 or more – you can use the healthy weight calculator to work out your BMI
  • you have previously had a baby who weighed 4.5kg (10lbs) or more at birth – the medical term for a birth weight of more than 4kg (8.8lbs) is macrosomic
  • you had gestational diabetes in a previous pregnancy
  • you have a family history of diabetes – one of your parents or siblings has diabetes
  • your family origins are South Asian (specifically India, Pakistan or Bangladesh), black Caribbean or Middle Eastern (specifically Saudi Arabia, United Arab Emirates, Iraq, Jordan, Syria, Oman, Qatar, Kuwait, Lebanon or Egypt)

Page last reviewed: 07/08/2014

Next review due: 07/08/2016