Gestational diabetes: the sugar test and what it means

Gestational diabetes is high blood sugar that starts in pregnancy. It happens when your body cannot make enough insulin for the extra needs of pregnancy. It is not caused by eating too many sweets, and most people who have it go on to have healthy pregnancies and healthy babies.

Who is offered a test?

You are offered a test if you have any of these risk factors, which your midwife checks at your booking appointment:

• A BMI above 30
• A previous baby weighing 4.5kg (about 10lb) or more at birth
• Gestational diabetes in an earlier pregnancy
• A parent, brother or sister with diabetes
• A family background that is South Asian, Black (African-Caribbean) or Middle Eastern. The risk is higher even if you were born in the UK.

Many people have no symptoms. Some notice being very thirsty, needing to pee a lot, a dry mouth, tiredness, blurred vision or thrush, but these are common in pregnancy anyway.

The test (OGTT)

The glucose tolerance test is a 2-hour test. You do not eat overnight (water is fine). A blood sample is taken, you drink a sugary drink, you rest, and another sample is taken 2 hours later. It is usually at 24 to 28 weeks. If you had gestational diabetes before, you are offered a test or a finger-prick kit earlier, soon after booking, and a repeat at 24 to 28 weeks if the first is normal. NICE says gestational diabetes is diagnosed if the fasting result is 5.6 mmol/l or higher, or the 2-hour result is 7.8 mmol/l or higher.

If you are diagnosed

• You get a blood sugar testing kit and a plan from a specialist team.
• Food and activity changes come first. A short walk after meals can help. Ask your team before starting anything new.
• If that does not bring your levels down enough, you may be offered tablets or insulin. This is common, and your team will explain what suits you and your baby.
• You will usually have extra scans to check your baby’s growth.
• Birth is usually advised before 41 weeks, earlier if there are concerns.

After the baby

Gestational diabetes usually goes away after birth, but it raises your chance of type 2 diabetes later. You should be offered a blood test 6 to 13 weeks after birth (this may happen at your 6-week check), and then a check every year. A healthy-weight, active life and the NHS Diabetes Prevention Programme can help lower your risk.