Gestational Diabetes


Diabetes: A group of metabolic diseases in which there are high blood sugar levels over a prolonged period. Two types Diabetes Mellitus Type I (autoimmune destruction of beta cells in the pancreas) and Type II (insulin resistance followed by beta cell atrohpy)
Gestational Diabetes: diabetes diagnosed during the second half of pregnancy with no prior existing diabetes.

Overview affects 5-10% of pregnancies. Incidence varies between nutritional and genetic factors. Risk of GDM increases with age. Women born in Southern Asia are at particularly higher risk. 50% change of mother to develop Type II Diabetes later in life.

Pregnancy Physiology

Risk Factors

Risk Factors
Previous GDM
Increase BMI
Maternal age >40yo
Family history
Polycystic ovarian syndrome
Low fibre diet
Weight gain as young adult
Current use of glucocorticoids and antipsychotics?


Signs and Symptoms

Clinical Presentation generally asymptomatic

Classic signs of Type II Diabetes (4P's)

  • Polyphagia
  • Polydipsia
  • Parasaethsia
  • Polyuria



In Australia oral glucose tolerance test (75g) at 24 and 28weeks.

  • Test at 1 hour >10 or 2 hour >8.5
  • Fasting glucose 5.1 hour
Diagnosing diabetes mellitus in pregnancy: The 7/11 rule. Fasting plasma glucose >7mmol/L and random BGL >11 mmol/L with symptoms of diabetes mellitus
Remember it is important to test for gestational diabetes because it can cause congenital abnormalities, miscarriages,  organomegaly, hydramnios, pre-eclampsia, maternal and infant birth trauma, perinatal mortality and neonatal metabolic and respiratory problems.


Normal Physiology

  • Maternal metabolism switches from carbohydrates to fat utilisation
  • Subsequent pancreatic beta cell hyperplasia
  • Increased insulin secretion
  • Early increase in insulin sensitivity causes progressive insulin resistance.



  • Placenta produces growth hormone, CRH,  placental lactinogen and progesterone.
  • These hormones promote glucose intake by the fetus by causing insulin resistance in the mother
  • Hyperglycaemia in circulation eventually cause the release of fetal insulin causing insulinaemia


Management Diagnosis GDM then management of a multidisciplinary team (i.e endocrinologist, diabetic educator).

  • Monthly ultrasound to check for foetal macrosomia.
  • Diet, exercise and blood glucose monitoring.
  • If glucose unstable change to insulin.
  • Induction of labour if continuously unstable gestational diabetes before term or early at term - to prevent complications
  • Postpartum (after delivery) stop insulin and glucose infusions, check blood glucose prior to discharge, follow up 6 weeks for oral glucose tolerance test, educate (as 50% risk of developing diabetes mellitus over the next 25years).


Remember Why treat GDM? Reduction in composite outcome of death, shoulder dystocia, bone fracture and nerve palsy. Reduction in infants weighing >90th birth-centile.

Complications and Prognosis