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Gestational diabetes - Dr Tan Toh Lick discusses what it means for you and your baby

Gestational diabetes mellitus (GDM) is diabetes that develops during pregnancy. GDM typically develops in the second or third trimester as a result of insufficient increase in insulin hormone production to meet pregnancy needs. 
GDM is very common affecting 1 in 4 pregnancy in Singapore 1. Women who are obese, have a previous GDM, have a previous large baby, have a family history of diabetes or are of some ethnic origin including South Asian and Chinese are more likely to develop GDM2.

Pregnant women are now recommended to have an oral glucose tolerance test (OGTT) around 24 – 28 weeks gestation particularly if they have risk factors3. This involves fasting from mid-night and having a blood test done in the morning. After the first blood test is taken, a glucose drink is given, and the blood test is repeated at 1 and 2 hours later to see if the blood sugar level is high. GDM is diagnosed if any of the blood sugar is high: fasting ≥5.2 mmol/l, 1-hour ≥10 mmol/l, 2-hour ≥8.5 mmol/l using the International Association of Diabetes and Pregnancy study group (IADPSG) criteria 4. This or another similar test such as self-monitoring of blood glucose may be done earlier at the booking visit if the woman has previous GDM, or shows signs of diabetes such as a large baby (macrosomia), increase amniotic fluid level (polyhydramnios), sugar in the urine, or recurrent infection2.

While most pregnancy complicated by GDM will have healthy babies, occasionally GDM can lead to serious problems if it is not managed. The baby may grow to be very big leading to difficulty birth, birth trauma, and the need for operative delivery. In addition, the baby may have low blood sugar after birth as it has been producing extra insulin in the womb. Furthermore, the baby may also develop obesity and diabetes in later life. Pregnancy with GDM may also be complicated by stillbirth.

Healthy eating and exercise can reduce the complications of GDM. Consuming food with a low glycaemic index (GI) and a low glycaemic load (GL) will minimize a rise in circulating blood sugar 2. Women with GDM should have a 30-minute stroll and monitor their blood sugar level before and after meals 2. A finger prick blood glucose of <5.5 mmol/l pre-meal, 7.8 mmol/l 1-hour post meal, and <6.7 mmol/l 2-hour post meal is desired 2.If the blood sugar is not controlled with diet and exercise, or if fasting plasma glucose is ≥7.0 mmol/l, or if it is between 6.0 – 6.9 mmol/l and associated with complications such as macrosomia or polyhydramnios, then medication is required 2. Referral to an endocrinologist and dietician is ideal 2. Metformin or insulin may be required in about 1 in 5 women with GDM. The baby will also require monitoring with regular ultrasound scans every 4 weeks from 28 weeks to monitor its growth and liquor volume 2,3. After 38 weeks, fetal well-being monitoring with CTG and fetal dopplers is also recommended2.

If the GDM is well controlled, delivery may be planned around 38 – 40 weeks. Vaginal delivery is feasible unless there is other indication for caesarean section, or if the baby is suspected to be too big for vaginal delivery. During labour, the blood sugar level should be monitored at least every 4 hourly to maintain at 4 – 7 mmol/l and the baby’s heart rate continuously monitored 2,3.

After birth, medication for GDM may be stopped but blood sugar levels monitored to ensure that they remain normal 2,3. The baby’s blood sugar will also be monitored a few hours after birth and for the first 48 hours to ensure it is not too low 2. Feeding the baby as soon as possible after birth and every 2-3 hours will help the baby maintain a safe sugar level 2.

Women with GDM will be offered fasting plasma glucose test at about 6 – 13 weeks after delivery 2. The majority will have a normal result, but some women will continue to have diabetes and require care. Women with normal result will also be advised to have 1 – 3 yearly fasting plasma glucose test and HbA1c as a third may go on to develop diabetes 2,3. Maintaining a healthy low GI and low GL diet with regular exercise will reduce the risk of developing diabetes in future.

Pre-conception health check is important. Women with a history of GDM planning to conceive again should optimize their health, weight, diet and exercise regime as well as take folic acid 5 mg daily to improve the chance of a successful pregnancy 2.

Dr Tan Toh Lick graduated from King’s College School of Medicine and Dentistry, the University of London in 1997. He undertook his Obstetrics and Gynaecology Specialist Training in London and was appointed Consultant Obstetrician and Gynaecologist in 2008. As a consultant, his contributions to service development, patient care and staff training were widely recognised and he was awarded 3 Clinical Excellence Awards in 2010 and 2012 in the United Kingdom. After he relocated to Singapore in 2013, he was awarded the Singapore Health Quality Service Award in 2015, Singapore.

Dr Tan now consults at Thomson Women’s Clinic (JEM) and Thomson Wellth Clinic (Pacific Plaza). He continues to be active in his academic work organizing 2 CME courses “Your Woman Matters” for family physicians and “PROMPT4 – The Tetralogy” for maternity specialists, as well as publishing in medical journals and public magazines.


HAPO Study Cooperative Research Group. Frequency of gestational diabetes mellitus at collaborating centers based on IADPSG consensus panel-recommended criteria: the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study. Diabetes Care. 2012 Mar;35(3):526-8

2 Diabetes in Pregnancy: Management of Diabetes and Its Complications from Pre-Conception to the Postnatal Period. [(accessed on 29 May 2019)]; Available online:

Ministry of Health Clinical Practice Guidelines: Diabetes Mellitus. SMJ. 2014; 55(6): 334-347

HAPO Study Cooperative Research Group. Hyperglycaemia and adverse pregnancy outcomes. New England J of Medicine. 2008;358(19):1991–2002