Gestational Diabetes Mellitus (GDM)

Gestational diabetes mellitus is glucose intolerance that is first recognised during pregnancy.

Screening for gestational diabetes is performed at 24 – 28 weeks.

• Rule of 15s
  1. 15% of pregnant women will have a positive 50g 1h screen
  2. Of these pregnant women, 15% will have GDM
  3. Of these pregnant women with GDM, 15% will require insulin

Classification of gestational diabetes

• Risk factors
  • Gestational diabetes in a previous pregnancy
  • Family history of gestational diabetes
  • BMI > 25 kg/m2
  • Physical inactivity
  • Age > 35 years
  • Prior macrosomic (> 4.5 kg)
    • Possibly due to previous undiagnosed gestational diabetes mellitus
  • Prior malformed or stillborn infant
    • Possibly due to previous undiagnosed gestational diabetes mellitus
  • Obesity
  • Hypertension
  • Cardiovascular disease
  • Polycystic ovarian syndrome (PCOS)
  • HbA1C > 5.7%
  • Acanthosis nigricans
  • HDL < 35 mg/dL
  • Triglycerides > 250 mg/dL
• Pathophysiology
  • Placental hormones, e.g., human placental lactogen (hPL), progesterone, and oestrogen, causes insulin resistance
  • Maternal pancreatic beta cells undergo hyperplasia in response to the reduced insulin sensitivity → increase in maternal insulin
  • Increased insulin results in hyperglycemia
  • Glucose crossess the placenta leading to:
    • Fetal hyperglycaemia
    • Fetal hyperinsulinaemia
    • Excess fetal growth (macrosomia)
• Signs and symptoms
  • Obesity
  • Excessive gestational weight gain
• Investigations
  • One-step approach
    • 75 g oral glucose tolerance test
      • The diagnosis is made with any exceeding value
      • Fasting glucose ≥ 5.3 mmol/L
      • 1 hour glucose ≥ 10.0 mmol/L
      • 2 hour glucose ≥ 8.6 mmol/L
  • Two-step approach
    • Non-fasting 50 g glucose challenge test for screening
      • Threshold depnds on local practice
      • It ranges from > 7.2 – 7.8 mmol/L
    • Fasting 100 g oral glucose tolerance test for diagnosis
      • ≥ 2 abnormal values are needed to diagnose
      • Fasting glucose ≥ 5.3 mmol/L
      • 1 hour glucose ≥ 10.0 mmol/L
      • 2 hour glucose ≥ 8.6 mmol/L
      • 3 hour glucose ≥ 7.8 mmol/L
    • Overt diabetes if fasting glucose is > 7.0 mmol/L
• Treatment
  • Dietary restriction
  • Exercise
  • Weight management
  • Home glucose monitoring 4 times a day -fasting and three post-prandial checks
    • Fasting target is < 5 mmol/L
    • 1-hour post-prandial target is < 7.8 mmol/L
    • 2-hour post-prandial target is < 6.7 mmol/L
  • Insulin is the first-line drug
    • 2/3 intermediate-acting insulin (NPH or Lente) in the morning
    • 1/3 short-acting insulin (Regular) in the evening
  • Oral glucose lowering agents (metformin and glyburide) can also be used
  • Weekly non-stress test and biophysical profile from 32 – 36 weeks
  • Obstetric ultrasound for fetal weight at 34 – 37 weeks
    • Caesarean delivery is recommended if the estimated weight is ≥ 4500 g
  • Delivery
    • Schedule delivery at 39 – 40 weeks for good glycaemic control
    • Schedule delivery at 37 – 39 weeks for poor glycaemic control after amniocentesis confirms foetal lung maturity
  • Follow up
    • Screen for overt diabetes at first post-partum visit
    • Screen for T2DM every year
• Complications
  • Obstetric complications
    • Polyhydramnios
    • Pre-eclampsia
    • Postpartum haemorrhage
    • Increased C-section risk
    • Infections- UTIs, pyelonephritis, asymptomatic bacteriuria
  • Diabetic emergencies
    • Hypoglycemia
    • DKA
    • Diabetic coma
  • Fetal complications
    • Macrosomia
    • Traumatic delivery
    • Shoulder dystocia
    • Erb’s palsy
  • Neonatal complications
    • Hypoglycemia
    • Hyperbilirubinemia
  • Childhood complications
    • Increasing risk of childhood obesity
    • Increased risk of developing T2DM later in life

Positive 70g 2h OGTT

Positive 50g 1h OGTT

Positive 100g 3h OGTT