Gestational diabetes

Diabetes is a common and well-known health condition which means that a person has too much sugar – or glucose – in their blood. This is called hyperglycaemia. Gestational diabetes is a form of diabetes that can affect women during pregnancy. The condition is usually diagnosed during the third trimester, and most women who are affected can expect it to disappear after their baby is born.

Symptoms and diagnosis

There are often no clear signs that a woman has developed gestational diabetes, however having higher levels of glucose in the blood may produce certain symptoms:

  • Frequent urination
  • Tiredness
  • Increased thirst and a dry mouth
  • Recurrent infections, including yeast infections or thrush
  • Visual disturbances.

Because the signs are not always clear, screening for gestational diabetes may take place as early as your first antenatal appointment. The GP or midwife will ask if there is any family history of diabetes and may offer a blood test to check blood glucose levels. A GTT, or glucose tolerance test, may also be carried out around weeks 26-28. This is a blood test that is usually taken in the morning before you have had anything to eat. A glucose drink will be given, followed by another blood test after two hours to check how well the glucose is being tolerated.

If you have had gestational diabetes during a previous pregnancy, more care should be taken as it can recur. The GTT will be performed earlier, and even if the results are within the normal range, the test should be repeated at 28 weeks.


If you have gestational diabetes you will be shown how to monitor blood glucose levels. Many women find that they can control their condition by modifying their diet and taking exercise, although sometimes medication will be required.

Blood glucose is measured by checking the concentration of glucose in the blood and this is done by looking at the level of millimoles of glucose per litre of blood (mmol/l). You will be given your own mmol/l target and advice on when to test the levels.

It may also be necessary to make some changes to your diet, and a dietician will be the best person to advise on this. Eat at regular intervals without skipping meals and include foods that have a low glycaemic index (GI) as these will be absorbed more slowly into the blood. Low GI foods include basmati rice, pasta, new potatoes, sweet potato, oats and muesli. Other foods with a higher GI rating will be absorbed more quickly, causing a rise in blood sugar. Include plenty of fresh vegetables along with up to three portions of fruit, however avoid fruit juice.

Exercise is important because being active helps to lower blood sugar levels, so your healthcare team will be able to give advice on activity that is safe during pregnancy.

Other medications may be prescribed if diet and exercise alone are not effective in controlling gestational diabetes. The body naturally makes insulin within the pancreas to control levels of blood glucose and insulin injections can be used to help to control diabetes. Insulin is usually self-injected, so you will be shown the technique and how to store the insulin and safely dispose of the needles. Insulin is associated with low blood sugar levels – or hypoglycaemia, and you will be advised on the signs to look out for in case this occurs. Rapid-acting insulin is injected before or just after a meal and is fast-acting but not long-lasting. Basal insulin is usually injected first thing in the morning or at night, and works by helping to keep blood sugar stable all day, between meals. Insulin is considered safe to use in pregnancy however blood glucose levels must be carefully monitored throughout.

Complications and risks

If you have gestational diabetes there are certain risks for mother and baby, and it will be necessary to have a planned hospital birth. Blood sugar levels should be monitored hourly during labour, and if you have been taking insulin you may be given this intravenously as well as glucose to help keep the levels stable. After the birth your baby’s blood glucose will be checked and if the levels are low they may be tube-fed or given an intravenous drip, which is likely to involve taking baby to the neonatal unit.

There is also a higher risk of having a baby who is especially large for their gestational age, and a birth weight over 4kg is called macrosomia. This means that baby’s growth should be closely monitored, with extra ultrasound scans to look at the measurements and to check the level of amniotic fluid. If baby is looking large your midwife will discuss the possibility of a planned caesarean section. Larger babies are at risk of shoulder dystocia if a natural birth is attempted. This means that as the baby’s head emerges the shoulder gets stuck behind the mother’s hip bone, and they may be unable to breathe. If baby’s size and your blood glucose levels are satisfactory, you may be able to wait for labour to begin, otherwise the healthcare team may suggest an induction at around 38 weeks. Gestational diabetes carries an increased risk of having a premature baby, meaning that baby is born before 37 weeks. There is also a greater risk of miscarriage, as well as having a baby who is stillborn.

Most women who have gestational diabetes find that they are no longer affected once their baby is born, with blood glucose returning to normal levels, although the condition can return in future pregnancies so monitoring should begin at an early stage. However, it is important for the GP to continue to check your levels of blood glucose, because there is a higher risk of developing type 2 diabetes in later life. There is also an increased risk for the baby of developing diabetes as they get older, or of being classed as obese, with a body mass index greater than 30.

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