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Gestational diabetes mellitus (GDM) is a condition in which high blood sugar develops in women for the first time during pregnancy, because the body cannot produce enough insulin – a hormone that controls blood sugar levels – to meet the needs of pregnancy.
Pregnancy increases the risk of developing diabetes because of placental hormones. These placental hormones increase glucose levels and the body’s resistance to insulin. This condition can occur in nearly a quarter of pregnant women.
GDM usually starts in the second or third trimester and usually disappears after delivery.
If well-controlled, most women diagnosed with GDM will have normal pregnancies and babies. However, if not well-controlled, GDM has potential risks for both mother and baby. These risks are illustrated in the table below.
It is therefore important to diagnose and treat GDM optimally to reduce the above risks.
GDM usually does not give rise to any symptoms, but is detected by a blood test called an oral glucose tolerance test (OGTT) done in the second trimester.
When GDM goes undetected or untreated, the developing foetus may be larger than normal, or there might be more ‘water’ (amniotic fluid) in the womb than normal.
When blood glucose levels are very high, symptoms such as increased thirst, increased urination or weight loss may occur.
Steps can be taken to reduce the risk of having GDM both before and during pregnancy. This is important especially if you have risk factors for GDM, or if you have had GDM during a previous pregnancy.
Having a healthy, balanced diet and regular exercise before and during pregnancy is important. These steps will help to achieve and maintain a healthy weight before becoming pregnant. A body mass index (BMI) of 18.5 to 22.9 kg/m2 is considered to be within the healthy range.
Risk factors for GDM include:
Although the risk of GDM is higher in certain groups of women, it can happen to any woman in her pregnancy. In Singapore, all pregnant women will be offered screening for GDM with an
oral glucose tolerance test (OGTT) between 24 and 28 weeks of pregnancy.
If you have had GDM before, have glucose in the urine or symptoms suggestive of diabetes, the OGTT will be performed earlier in pregnancy and repeated again at 24 to 28 weeks if the first test was normal.
Detection of GDM is important so that appropriate treatment can be given to reduce the risks to the pregnancy.
An OGTT to diagnose GDM requires:
GDM is diagnosed if any one of the three blood results indicate a higher than expected blood glucose level.
The standard glucose drink is sweet and may cause some to feel nauseated. In rare cases, it may trigger vomiting. If this happens, the test will need to be rescheduled to another day if you are agreeable.
All pregnant women are strongly encouraged to undergo the test as GDM is a common condition in pregnancy, and there are potential risks to the pregnancy if it is not detected and treated promptly.
Should you decline to do the test, please help us understand your reasons for not wanting to do so. We would like to reassure you that your decision, whatever it may be, will not affect your subsequent antenatal care.
When you have GDM, you will be under the care of a specialist healthcare team comprising obstetricians, endocrinologists, specialised nurses and dietitians.