What is gestational diabetes mellitus, why do women get it and how common is it?

In Singapore, about 15-20% of all pregnancies are complicated by gestational diabetes mellitus (GDM).

Pregnancy increases your risk of developing diabetes because of placental hormones. These increase your glucose levels and your body's resistance to insulin, which is important for the controlling of blood glucose.

“Gestational diabetes mellitus usually starts in the second or third trimester. It usually disappears after delivery,” says Dr Lim Weiying​, Associate Consultant, Department of Endocrinology, Singapore General Hospital (SGH), a member of the SingHealth​ group.

Risk factors for gestational diabetes mellitus

You are at a higher risk of gestational diabetes mellitus​ if you have:

  1. Body mass index (BMI) of 23 kg/m2 and above 
  2. First degree relatives (parents, siblings or children) with diabetes mellitus
  3. Personal history of previous gestational diabetes mellitus, or large babies weighing over 4 kg
  4. Previous poor pregnancy (obstetric) outcomes that are usually associated with diabetes, such as stillbirth

How does gestational diabetes mellitus affect you and your baby?

Most women with gestational diabetes mellitus have healthy pregnancies and babies. However, if not well-controlled, gestational diabetes mellitus has potential risks for both mother and baby.

There will be a higher chance of risk at these stages:

In pregnancy: In pregnancy:
  • Miscarriage
  • Pre-clampsia (high blood pressure during pregnancy)
  • Premature birth
  • Stillbirth
  • Birth defects
  • Excessive amniotic fluid
  • Large for gestational-age baby
At delivery: At delivery:
  • Induction of labour
  • Forceps / vacuum-assisted delivery
  • Caesarean section
  • Difficult / traumatic delivery
  • Shoulder dystocia
  • Birth injury
  • Breathing difficulties
After delivery: After delivery:
  • Wound complications
  • Bleeding problems
  • Risk of type 2 diabetes in future
  • Low blood glucose
  • Blood mineral imbalances
  • Jaundice
  • High-dependency or intensive care unit admission
  • Risk of obesity and/or diabetes


It is therefore important to diagnose and treat gestational diabetes mellitus optimally to reduce these risks.

See the next page to find out​ how to diagnose gestational diabetes mellitus.​

Ref: O17