Gestational diabetes: when and how is it tested? Antenatal check-ups at Maternal and Child Health Centres and the Hospital Authority, high-risk factors, what happens after diagnosis, and postnatal follow-up

When is gestational diabetes tested for?

The Antenatal Check-up Schedule in Maternal and Child Health Centres / Hospital Authority lists the ‘gestational diabetes test (if necessary)’ at 24 to 28 weeks of pregnancy, when routine antenatal check-ups are every 4 weeks; the test is provided by Hospital Authority obstetrics departments or Maternal and Child Health Centres, the schedule is for reference only, and healthcare professionals may arrange different check-up times according to the situation (Department of Health Family Health Service, May 2024).

The College supports universal screening by 75 g oral glucose tolerance test at 24 to 28 weeks of pregnancy as long as resources are available; if universal screening cannot be done, the College recommends offering the test to pregnant women with any risk factor, and to women who have clinical features related to hyperglycaemia in pregnancy, or who have risk factors but booked after 28 weeks (Hong Kong College of Obstetricians and Gynaecologists, ‘Guidelines for the Management of Gestational Diabetes Mellitus’, revised November 2016, for obstetricians and gynaecologists).

A urine test is done at every antenatal check-up, to check whether the urine contains sugar and protein so that health problems in pregnancy, such as diabetes or pre-eclampsia, can be found early; because of hormonal effects, a pregnant woman's urine may contain a little sugar even when she is normal, which is not necessarily gestational diabetes, and after assessment by a doctor, a blood test may be needed to confirm the diagnosis (Department of Health Family Health Service ‘Information to Antenatal Clients’ video transcript, November 2017). When blood glucose tests are done is arranged by healthcare professionals.

Which pregnant women are at high risk of gestational diabetes?

In general, pregnant women with high-risk factors for gestational diabetes need a blood glucose test (Department of Health Family Health Service video transcript, November 2017). The Hong Kong College of Obstetricians and Gynaecologists guideline (revised November 2016, for obstetricians and gynaecologists) separately lists a table of risk factors; the factors listed in the two documents are in the table below.

How is gestational diabetes diagnosed?

The guideline adopts the definition revised by the World Health Organization in 2013: hyperglycaemia first detected during pregnancy is classified as diabetes mellitus in pregnancy or gestational diabetes mellitus (GDM); after a 75 g glucose load, gestational diabetes can be diagnosed if any one of the following is met: fasting blood glucose of 5.1 to 6.9 mmol/L, 1-hour blood glucose of 10.0 mmol/L or above, or 2-hour blood glucose of 8.5 to 11.0 mmol/L (Hong Kong College of Obstetricians and Gynaecologists guideline, revised November 2016, for obstetricians and gynaecologists). Women who were already diagnosed with diabetes or pre-diabetes before pregnancy do not fall into this classification (Hong Kong College of Obstetricians and Gynaecologists guideline, revised November 2016). A fasting blood glucose of 7.0 mmol/L or above, or a 2-hour blood glucose of 11.1 mmol/L or above after a 75 g glucose load, is diabetes in pregnancy (Hong Kong College of Obstetricians and Gynaecologists guideline, revised November 2016). Results are interpreted by a doctor, and the treating doctor decides individual cases.

What happens after gestational diabetes is diagnosed?

A pregnant woman with gestational diabetes needs to control her diet appropriately, and a small number of pregnant women may need medicines; without appropriate treatment, there can be serious effects on the health of the pregnant woman and the foetus, such as high blood pressure or premature birth (Department of Health Family Health Service video transcript, November 2017).

Each unit should have a team including a dietitian, a diabetes nurse, an obstetrician and an endocrinologist to provide multidisciplinary care; all women diagnosed should be referred to a dietitian and taught about diet, exercise (for example walking for 30 minutes after a meal) and capillary blood glucose monitoring; if blood glucose targets are still not met after 1 to 2 weeks of diet and exercise therapy, metformin is recommended, with insulin added if needed (Hong Kong College of Obstetricians and Gynaecologists guideline, revised November 2016, for obstetricians and gynaecologists).

For choosing an endocrinologist, see How to choose an endocrinologist; Maternal and Fetal Medicine is a discipline within Obstetrics & Gynaecology that deals with high-risk pregnancies, perinatal problems, and medical and surgical complications that are unique to or uncommonly encountered in the pregnant woman or the foetus (Hong Kong Academy of Medicine, Specialty Descriptions, April 2025). The treatment of an individual pregnant woman is decided by the treating doctor.

Is follow-up needed after giving birth?

Women who were diagnosed with hyperglycaemia during pregnancy should be told that their risk of diabetes in future and of hyperglycaemia in the next pregnancy is increased, and should be offered lifestyle advice including weight control, diet and exercise; a test 6 to 12 weeks after the birth is recommended to exclude diabetes, repeated regularly according to risk: once a year for higher risk, and once every 3 years for lower risk (Hong Kong College of Obstetricians and Gynaecologists guideline, revised November 2016, for obstetricians and gynaecologists).

Women with a history of gestational diabetes or a big baby are among the risk factors for which screening for type 2 diabetes should be done; when risk factors are present, screening can be more frequent, for example every 12 months (Centre for Health Protection Non-Communicable Diseases Watch, November 2021, relaying the 2021 revised edition of the Hong Kong Reference Framework for Diabetes Care for Adults in Primary Care Settings). The treating doctor decides individual cases.

Public or private antenatal care?

Pregnant women can receive antenatal care at Hospital Authority obstetrics departments, Maternal and Child Health Centres or private healthcare institutions, and care includes screening for potential health problems in pregnancy such as high blood pressure and diabetes (Department of Health Family Health Service ‘Information on Antenatal Service’, February 2024). For public and private childbirth compared, see Giving birth: public or private hospital?, and for choosing an obstetrician and gynaecologist, see How to choose an obstetrician and gynaecologist.

After assessment, pregnant women are generally followed up at a Maternal and Child Health Centre; in high-risk situations such as twin pregnancy, diabetes or complications of pregnancy, follow-up is by the hospital (Department of Health Family Health Service video transcript, November 2017).

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