Gestational diabetes: the glucose test and what happens next

Gestational diabetes is raised blood glucose that begins in pregnancy

In pregnancy, hormones from the placenta make the body respond less to insulin, the hormone that moves glucose (sugar) from the blood into the cells. If the body cannot make enough extra insulin to compensate, blood glucose rises, and this is gestational diabetes.

It usually causes no symptoms, or ones easily mistaken for ordinary pregnancy such as thirst or tiredness, so it is found by testing.

Raised glucose crosses the placenta to the baby. Over time the baby may grow larger than expected, which can make the birth more difficult and makes induction or a cesarean more likely. It can also mean extra fluid around the baby, a higher chance of pre-eclampsia, and low blood glucose in the baby after birth. Keeping glucose on target lowers the chance of these problems.

Who has the glucose test, and when

NICE advises the test for pregnant women with at least one of these risk factors:

• A body mass index (BMI) above 30.
• A previous baby who weighed 4.5 kg or more at birth.
• Gestational diabetes in a previous pregnancy.
• A parent, brother or sister with diabetes.
• A family background in which diabetes is common, including Middle Eastern, South Asian and Black Caribbean families.

Because some of these factors are common, some hospitals and clinics test every pregnant woman.

The test is usually done between 24 and 28 weeks. Women who had gestational diabetes before are tested soon after the early antenatal visit, with the same test or with home glucose checks, and again at 24 to 28 weeks if that test was normal. Sugar in the urine at a routine check can also lead to testing.

What the glucose tolerance test involves

The usual test is the oral glucose tolerance test (OGTT), which takes about two hours. You are asked not to eat beforehand, usually overnight, though water is normally allowed. A blood sample is taken, you drink a sweet glucose drink, then wait quietly, without eating, for a second sample two hours later.

Some women feel slightly sick or light-headed after the drink, and a snack for afterwards can help. If you take regular medicines, ask beforehand whether to take them that morning.

If either reading is above the level NICE sets, the diagnosis is gestational diabetes. A normal test is reassuring for that stage, but glucose can rise later, so the test may be repeated if concerns appear.

What happens if the test shows gestational diabetes

Care usually begins with food and activity. A dietitian can help build meals around slower-release carbohydrates such as wholegrains, pulses and vegetables, in place of sugary drinks, sweets, and white bread or rice. A walk after meals helps too.

You also learn to check your glucose at home with a finger-prick meter, usually before breakfast and after meals, and the readings are reviewed at each visit.

If glucose stays above target after one or two weeks, medicine is added, usually metformin tablets and then insulin if needed. Insulin may be started sooner if glucose is well above target at diagnosis. Both are widely used in pregnancy, and their benefits and possible side effects are discussed before starting. Insulin can cause low blood glucose, so women using it learn to recognise and treat a low.

Extra scans check the baby’s growth and the fluid around the baby, usually every few weeks in the last three months.

If you plan to fast in Ramadan, raise it with your doctor well before the month begins. Fasting changes blood glucose through the day and the way medicines, especially insulin, need to be taken.

Planning the birth, and the checks that follow

If all is well, NICE advises giving birth by 40 weeks and 6 days, usually by induction if labour has not started, and earlier if glucose is hard to control or there are concerns about mother or baby. If scans suggest a large baby, induction, waiting for labour and a planned cesarean are discussed, with the benefits and risks of each.

During labour, glucose is checked regularly, sometimes with a drip to keep it steady. After the birth, gestational diabetes medicines are usually stopped, and the baby is fed soon and often, with blood glucose checks in the hours that follow.

Gestational diabetes usually goes away after the birth, but it leaves a higher chance of type 2 diabetes in later years and of gestational diabetes next time. NICE advises a blood glucose test 6 to 13 weeks after the birth, then a yearly test if that is normal. Keeping active and reaching a healthy weight lower the chance of type 2 diabetes, and telling your doctor early in a future pregnancy means glucose can be checked from the start.