Gestational Diabetes Mellitus (GDM) is a condition in which the body does not produce enough of the hormone insulin to control sugar levels during pregnancy. It is a common complication of pregnancy ranging from 10% to 20% of all pregnant women in Singapore.

WHAT ARE THE RISKS OF GESTATIONAL DIABETES MELLITUS?

GDM puts both mother and child at serious risks. The baby can have excessive weight gain (also known as macrosomia) and hypoglycaemia (low blood sugar) after birth, develop fetal abnormalities, and even succumb to sudden fetal death. The mother can develop high blood pressure and preeclampsia while pregnant, give birth prematurely and run the risk of getting Type 2 Diabetes Mellitus (DM) in her lifetime.

HOW TO DETECT GESTATIONAL DIABETES MELLITUS?

Screening for all pregnant women during pregnancy is the most effective way to detect and manage it early. The screening test for GDM is a three-point Oral Glucose Tolerance Test (OGTT).

After fasting overnight, the woman’s blood is taken and tested at three time-points at:

• Starting (Fasting); one hour; two hours after taking a flavoured sweet drink calibrated at 75-gram glucose load.

Any blood sugar levels above a certain criteria value for each of the three time-points is considered GDM. The criteria for each of the time-points are derived from an international study (HAPO Study) of which KK Women’s and Children’s Hospital (KKH) is one of the 15 main study centres.

WHEN IS THE BEST TIME TO DO OGTT?

The routine screening for GDM for pregnant women is best performed at 24 to 28 weeks. However, if there are any risk factors, e.g., persistent sugar in the urine or previous history of GDM on insulin, the screening may be done earlier.

WHAT IS THE TREATMENT FOR GESTATIONAL DIABETES MELLITUS?

The treatment of GDM varies, depending on the result of the OGTT. If the condition is mild, controlling the diet is often enough. For more severe cases, oral medications (metformin) or insulin injections (depending on severity) may be required for the remainder of the pregnancy.

A dietitian will advise on a sensible eating plan, which is to have a healthy diet and foods with a low glycaemic index. Regular exercise (such as walking for 30 minutes after a meal) to improve glycaemic control is recommended. Women with GDM should have regular monitoring of fetal growth and deliver by full-term.

WHAT FOLLOW-UP ACTION IS REQUIRED AFTER DELIVERY FOR WOMEN WITH GDM DURING PREGNANCY?

Women with GDM should be encouraged and supported to breastfeed as breastfeeding reduces risk of obesity and diabetes in the children. The dose of metformin, glibenclamide and/or insulin may be reduced or stopped after birth as indicated.

A repeat OGTT (two-point test) should be performed 6 weeks after delivery, with a follow-up in the clinic to ensure that the high sugar level has resolved. This can exclude existing Type 2 DM and will also identify women with impaired glucose tolerance, for whom referral for more active follow-up and intervention is required.

Even if the postnatal OGTT is normal, women with a history of GDM should be informed about the increased risk of developing Type 2 DM in her lifetime and hyperglycaemia in subsequent pregnancies, and should be offered lifestyle advice that includes weight control, diet and exercise.

Women with background risk factors (e.g., obesity, strong family history of Type 2 DM, insulin required during pregnancy, metabolic syndrome etc.) should have more frequent screening (yearly) than those at lower risk (once every 2 to 3 years).

WHY IS IT IMPORTANT TO FOLLOW UP AFTER DELIVERY?

Although GDM resolves in most women after their pregnancy, these women still have a much higher risk of developing Type 2 DM in their lifetime. Type 2 DM, if not detected early or not well-controlled, can be associated with permanent complications to the kidneys, eyes and blood vessels.

There is evidence that certain lifestyle changes to diet and exercise can help delay or even prevent the development of Type 2 DM after GDM. Follow-up after delivery is therefore important for detecting persisting or the onset of Type 2 DM, in order to achieve prompt and optimal control and treatment of the condition.

WHAT ARE THE MEASURES TO REDUCE THE FUTURE RISK OF TYPE 2 DM?

The main ways to reduce the risk of developing Type 2 DM after GDM are sensible eating and regular exercise, both of which contribute to reducing body weight and Body Mass Index (BMI). A high BMI is associated with an increased risk of developing Type 2 DM.

Weight loss should be slow, steady and sustained. The recommended rate of weight loss is 0.5 to 1kg per week. A reduction of 7% body weight in 6 months is a safe and effective weight loss goal.

GPs can call for appointments through the KKH Central Appointments Hotline at 6294 4050 for more information.

By: Professor Tan Kok Hian, Head and Senior Consultant, Perinatal Audit and Epidemiology Unit, Division of Obstetrics and Gynaecology, KK Women’s and Children’s Hospital

Professor Tan Kok Hian is the Head and Senior Consultant of the Perinatal Audit and Epidemiology Unit, Department of Maternal Fetal Medicine, KK Women’s and Children’s Hospital (KKH). Professor Tan is also the Lead for Gestational Diabetes Mellitus (GDM) at the SingHealth Duke-NUS Diabetes Centre and the Lead Principal Investigator of the NMRC-funded Integrated Platform for Research in Advancing Metabolic Health Outcomes of Women and Children (IPRAMHO).

Professor Tan initiated universal screening for GDM, and the new International Association of Diabetes and Pregnancy Study Groups criteria, in KKH and Singapore General Hospital since January 2016 - based on a cost-effectiveness study of GDM screening under the Growing Up towards Healthy Outcomes (GUSTO) study. He is also the Chairperson of the College of Obstetricians and Gynaecologists, Singapore GDM Committee 2017-2018 and Chairperson, Expert Group GDM Appropriate Care Guide of the Agency for Care Effectiveness, Ministry of Health 2017-2018.

References

1. Tan KH, Tan T, Chi C, Thian S, Tan LK, Yong TT. Guidelines for the Management of Gestational Diabetes Mellitus. College of Obstetricians
and Gynaecologists, Singapore. Singapore Journal of Obstetrics & Gynaecology. 2018; 49(1):9-13 2. Chen PY, Finkelstein EA, Ng MJ, Yap F, Yeo GS, Rajadurai VS, Chong YS, Gluckman PD, Saw SM, Kwek KY, Tan KH. Incremental Cost-Effectiveness Analysis of Gestational Diabetes Mellitus Screening Strategies in Singapore. Asia-Pacific Journal of Public Health 2016; 28(1):15-25
3. Chong YS, Cai S, Lin H, Soh SE, Lee YS, Leow MK, Chan YH, Chen L, Holbrook JD, Tan KH, Rajadurai VS, Yeo GS, Kramer MS, Saw SM, Gluckman PD, Godfrey KM, Kwek K; GUSTO study group. Ethnic differences translate to inadequacy of high-risk screening for gestational diabetes mellitus in an Asian population: a cohort study. BMC Pregnancy Childbirth. 2014 Oct 2;14:345
4. HAPO Study Cooperative Research Group Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. 2008 May 8;358(19):1991- 2002.