Role of HbA1c and 50g GCT in early detection and prediction of gestational diabetes and associated maternal and fetal complications in Thailand High blood glucose levels in pregnancy called gestational diabetes mellitus (GDM) is one of the most common medical conditions during pregnancy. It can cause harm to the pregnant woman and her child. GDM affects 10-15% of Thai women. More women are being diagnosed with GDM now because a lower level of blood glucose is being used to diagnose GDM.  If not treated, GDM can cause high blood pressure in pregnancy, increased numbers of caesarean deliveries, anxiety and depression. Women who have had GDM have 7-8 times higher life-time risk of type 2 diabetes mellitus (T2DM). There are risks to the children too. They may be too big or too small. If too big, they can have shoulders damaged during the birth. Their blood glucose may fall too low after birth. They may get jaundice soon after birth, or have difficulty in breathing. A very few may die before birth (stillbirth). In the long term, these children are at higher risk of becoming overweight and diabetic.  The diagnosis of GDM is usually made between 24-28 weeks of pregnancy using a glucose drink test called an oral glucose tolerance test (OGTT). Although treatment can improve pregnancy outcomes, some of the damage may have already been done to the unborn baby.  So screening to detect high glucose levels earlier in pregnancy may be better. However, there can be harms as well as benefits from screening. As a recent British Medical Journal article said:  "a label of gestational diabetes brings with it an intervention package that includes glucose monitoring, extra clinic visits, more obstetric monitoring with greater likelihood of labour induction, operative delivery and admission of the baby to special care, and finally for the mother a label of high risk for diabetes".   Some people think that all women should be screened with OGTT has been advocated but that may not be needed. The test requires pregnant women to come to a clinic having not eaten anything for at least 8 hours. In many countries including the UK, women are selected for OGTT based on risk factors such as overweight and older age. However, selecting women based on these factors can miss up to half of all women with GDM.   In Thailand, women at high risk for GDM are supposed to be screened at the first antenatal clinic visit with the 50g Glucose Challenge Test (GCT). But, the rate of screening for GDM in Thailand varies from none at all in rural areas to 78% in cities.   Another blood glucose test done by a simple finger prick (called HbA1c) might do instead. It would be done at the first antenatal clinic visit. The HbA1c is a one-step test and patients do not need to fast. However, the value of HbA1c testing is not yet known in Thai women.  The aims of this study are to find out whether HbA1c and 50g GCT testing at first antenatal clinic visit can predict later GDM and if there is a level that can rule out later GDM. We also want to compare testing of all pregnant women with testing only those with risk factors. We will do a trial to see if diet and lifestyle interventions can prevent women developing GDM.  Accurate HbA1c and 50g GCT levels that can safely rule out GDM in women at low risk would help pregnant women. They can be reassured. Avoiding the need for OGTT would save them time and money. In contrast, if the HbA1c and 50g GCT levels identifies them as at high-risk, healthy eating and lifestyle advice can reduce their risk of getting GDM. In addition to the benefit to mothers and their children, this study will also be useful to people who provide health care in Thailand. They can focus care more on women at high risk. The results could be used by other countries. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.