Pregnancy blood tests – testing for diabetes

Pregnancy (antenatal) blood tests are carried out during pregnancy to check on the health of you and your baby. Initial screening for diabetes is also carried out at the same time.

Why is screening for diabetes important during pregnancy?

Diabetes is a medical condition where the glucose levels in the bloodstream run too high. You may already know that you have this, or may be diagnosed for the first time when you have your first antenatal screen. More commonly, you may develop diabetes for the first time during pregnancy (called gestational diabetes).

Gestational diabetes usually goes away after your baby has been born, but often occurs again in future pregnancies. It may also put you at higher risk of developing diabetes in later life. Any kind of diabetes can be serious in pregnancy, although pregnancies that happen when you already have diabetes more commonly have problems for you or your baby.

If your glucose levels get too high, this puts you at risk of short term problems such as infection or even coma. In the long term it may damage your organs, such as your eyes or kidneys. Diabetes that is already present when the baby is conceived, even if you do not know about it, puts the baby at higher risk of miscarriage or birth defects. All kinds of diabetes, if untreated, can make the baby grow too large to be delivered safely, increase the risk of stillbirth (the baby dying in your tummy) or affect the health of your baby long-term.

Tests to detect diabetes in pregnancy

HbA1c

This is a one-off blood test, usually performed with the first routine antenatal screen, which shows if your blood sugar levels have been persistently high in the last 6 weeks. If it is very high, you will be diagnosed with pre-existing diabetes. If it is moderately raised, you are at increased risk of developing gestational diabetes, and should have a full 2 hour diagnostic test at 24-28 weeks.

1 hour 'Polycose' glucose challenge blood test

This should only be done if your HbA1c was low, and you have no personal or family history that would increase your risk of gestational diabetes, as it may miss diabetes in up to a quarter of pregnant women.

2 hour OGTT (oral glucose tolerance test)

This is recommended if you have any risk factors for developing diabetes, and in some countries is the only testing performed for diabetes in pregnancy. It does take 2 hours to perform, and requires 3 blood tests.

What if I am diagnosed with diabetes during pregnancy

If you are diagnosed with diabetes at any stage of your pregnancy, you will be referred to a specialist to discuss how to reduce these risks for you and your baby. You will be encouraged to keep active and eat healthily, and monitoring of your blood glucose levels will be recommended. Some women need treatment to reduce high levels of glucose, which may be either with tablets or insulin injections.

Learn more

Testing for diabetes in pregnancy Ministry of Health, NZ
Diabetes and pregnancy PatientInfo, UK

Reviewed by

Dr Janet Crofts is an obstetrician with further specialisation in maternal-fetal medicine. She is currently based in Auckland, and has trained in the UK, New Zealand and Australia.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Janet Crofts, Obstetrician, Auckland Last reviewed: 14 Feb 2022