Gestational diabetes is a state of insulin resistance induced by the metabolic strain of pregnancy

Aetiology

• Usually diagnosed at 24-28 weeks of gestation

Risk factors

The NICE guidelines list the risk factors that warrant testing for gestational diabetes:

• Previous gestational diabetes
• Previous macrosomic baby (≥ 4.5kg)
• BMI > 30
• Ethnic origin (black Caribbean, Middle Eastern and South Asian)
• Family history of diabetes (first-degree relative)

Investigations

• Oral glucose tolerance test (OGTT): the screening test of choice for gestational diabetes
  • It is used in patients with risk factors for gestational diabetes, and also when there are features of the foetus/pregnancy that suggest gestational diabetes:
    • Large for dates fetus
    • Polyhydramnios
    • Glucose on urine dipstick

Management

• Treatment is with a low GI diet, plus metformin and insulin if required
• The risk of future type 2 diabetes can be addressed with diet, lifestyle and metformin therapy
• Women with gestational diabetes should give birth no later than 40+6 weeks of gestation
• GDM usually tends to disappear as soon as the placenta is delivered

Complications

• There is a clear association with raised blood glucose levels in pregnancy and complications such as congenital malformations, large baby size and obstetric complications with increased rates of miscarriage and stillbirth
• Hyperglycaemia in pregnancy is associated with an increased later risk of developing type 2 diabetes in up to 50% of women over the next 5-10 years