Diabetes is a condition in which glucose (sugar) levels in the blood are high, due to either decreased production of insulin by the pancreas or increased resistance to insulin in other tissues.

What Is Gestational Diabetes?

Gestational diabetes is when women who are not known to be diabetic develop high glucose levels in their blood in the later part of their pregnancy. Gestational diabetes affects 4% of all pregnant women.

What Causes Gestational Diabetes?

The placenta helps provide and deliver nutrients to the baby and the hormones produced by it help the baby grow. Hormones (growth hormone and cortisol) released by the placenta after 24 weeks cause an increase in blood glucose levels but they block the action of insulin in the mother, causing insulin resistance. The mother has to produce up to three times more insulin to counter the effects of these hormones and most women are able to do so. It is not clear why some women are unable to produce the required amount of insulin and if this happens, blood sugars rise (hyperglycaemia) as there is not enough insulin to take the glucose out of the blood and in to the tissues.

How Does This Affect The Baby?

As the high glucose levels occur later in pregnancy, after the baby has been formed, gestational diabetes does not cause as many birth defects as may be seen in babies born to mothers who have been diabetic from the beginning. There is an increased chance of developing abnormalities in the central nervous system (neural tube defects) and an increased risk of stillbirth and neo-natal death.

As glucose passes across the placenta and insulin does not, blood glucose levels in the baby rise. This is stored as fat in the baby and can lead to macrosomia (large babies). A large baby can mean an increased chance of injuries at birth both to mother and to baby, including damage to babies shoulders and nerves in their arms¹. It also leads to an increased chance of having a caesarean section delivery and going into early labour.

The increased glucose flowing across the placenta causes the baby to produce more insulin to counteract it. After birth the baby no longer has this extrinsic source of glucose and the extra insulin can cause its blood glucose to fall (hypoglycaemia).

There is an increased risk of jaundice, low magnesium and low calcium levels. There is also a higher risk of breathing problems, as their lungs have not matured as normal. This usually resolves with time.

Later effects include childhood obesity and adult onset (type 2) diabetes.

How Does This Affect The Mother?

Gestational diabetes is not an immediate threat to the mother's health. Most women with gestational diabetes whose blood sugar levels stay within the safe range deliver their babies without complications. However, in some women it can result in high blood pressure, pre-eclampsia and urinary tract infections.

What Are The Risk Factors?

Although there is no clear reason why some women get gestational diabetes, women are more at risk if they:

• Have a family history of type 2 (adult-onset) diabetes
• Have previous impaired glucose tolerance
• Have high blood pressure
• Are over the age of 35
• Are obese
• Have previously given birth to a large baby
• Have previously given birth to a baby with an abnormality
• Have previously had a stillbirth late in pregnancy

About half the women who develop gestational diabetes have none of the above risk factors.

What Are the Symptoms?

In most women, gestational diabetes causes no symptoms. Some women do get symptoms of high blood sugar, such as increased thirst, increased need to pass water and increased hunger, although these are also common later on in pregnancy anyway.

How Is Gestational Diabetes Diagnosed?

Urine is routinely tested for sugar throughout pregnancy, and high blood sugar, if present, is usually detected between 24 and 28 weeks of pregnancy.

The only way to confirm gestational diabetes is with a glucose tolerance test, which needs to be carried out after eight hours without food. The mother is given a solution of glucose to drink, and then blood samples are taken and analysed at different intervals to see how the body deals with the glucose over time.

What Is The Treatment?

The aim of treatment is to keep blood glucose levels as close to normal as possible. Glucose levels are monitored with regular blood tests, which may need to be done daily with finger-prick tests carried out at home.

Treatment plans include controlling dietary intake of carbohydrates (sugar) and gentle regular exercise. Insulin injections may also be considered depending on severity.

What Happens After The Baby Is Born?

Gestational diabetes usually goes away after pregnancy. There is, however, a 66% chance of recurrence in future pregnancies. There is a link between gestational diabetes and the development of type 2 diabetes later in life. This may be due to the similar mechanism ie insulin resistance.

Some so-called gestational diabetes is straight forward diabetes that happens to have been picked up during pregnancy. This would obviously require further investigation and management.