Gestational Diabetes Mellitus (GDM) is a type of diabetes that develops only during pregnancy. It’s diagnosed when higher-than-normal blood sugar levels first appear while you are expecting.

Around 5% (1 in 20) pregnant women will develop GDM — most often between the 24th and 28th week of pregnancy, although it can occur earlier.

Detecting and managing GDM early helps keep both you and your baby healthy.

Who’s at Higher Risk?

You may be more likely to develop GDM if you:

• Have a family history of Type 2 diabetes
• Are overweight
• Had GDM during a previous pregnancy
• Are over 30 years old
• Have had past pregnancy complications
• Are from an Indian, Vietnamese, Chinese, Middle Eastern, Polynesian/Melanesian background
• Are an Indigenous Australian or Torres Strait Islander
• Have glucose detected in your urine
• Are expecting twins or multiples

Why Does GDM Happen?

During pregnancy, your placenta produces hormones that help your baby grow. These hormones also make it harder for your body to use insulin — this is called insulin resistance.

Your insulin needs can become 2–3 times higher than usual.

If your body can’t keep up with that demand, your blood sugar rises and GDM develops. After your baby is born, insulin needs usually return to normal and GDM goes away.

How We Test for GDM

When:

• All women are screened between 24–28 weeks, or earlier if risk factors are present.

Step 1 – Screening Test

• Eat and drink normally before the test
• Drink a 50g glucose drink
• 1 hour later, your blood sugar level is checked
• If your reading is over 7.8 mmol/L, we’ll arrange the confirmatory test

Step 2 – Oral Glucose Tolerance Test (OGTT)

• Eat a normal diet with at least 300 g of carbs for 3 days before
• Fast for 8 hours before the test
• Fasting blood sample taken
• Drink a 75g glucose drink
• Blood samples taken at 1 hour and 2 hours
• A result of:
  • Fasting sugar ≥ 5.5 mmol/L, OR
  • 2-hour sugar ≥ 8 mmol/L
    confirms GDM and we’ll guide your treatment plan

Managing GDM

Treatment is a team approach — involving you, your partner, your doctor, a dietitian, and a diabetes educator.

1. Lifestyle changes – Adjusting eating patterns, physical activity, and regular blood sugar checks.
2. Insulin therapy – Only if diet and activity alone don’t keep sugar levels within target.
3. Hospital care – In rare cases if levels remain high despite treatment.

Possible Risks if GDM Isn’t Controlled

• Large baby (over 4.5 kg)
  • May cause difficult birth or shoulder dystocia
  • May require caesarean section
• Slightly increased risk of stillbirth
• For the baby:
  • Low blood sugar after birth
  • Low calcium/magnesium
  • Jaundice
  • Breathing problems
  • Higher red blood cell count
• Babies of mothers with GDM are not born with diabetes, but have a higher future risk.

After Your Baby Is Born

• GDM usually disappears after birth
• We’ll arrange a 6-week postpartum OGTT to ensure your blood sugars are normal
• Future care:
  • Healthy eating and activity
  • Maintain ideal weight
  • Blood sugar checks every 2–3 years
• Women who’ve had GDM have a 30–50% chance of developing Type 2 diabetes within 15 years — healthy lifestyle choices can reduce this risk

Additional support and information can be found via:

• Diabetes Australia contact: 1300 136 588
• NDSS website: www.ndss.com.au
• Diabetes Australia Gestational Diabetes

resources: https://www.diabetesaustralia.com.au/managing- diabetes/gestational/

For updated clinical guidance or patient education, you can also explore:

• UpToDate patient information on Gestational Diabetes for detailed clinical outlines: www.uptodate.com

These resources are ideal for patients and healthcare providers to support safe pregnancy and management of gestational diabetes