Diabetes in pregnancy is generally classified as either hyperglycaemia in pregnancy (gestational diabetes or DM in pregnancy) or pre-gestational (type 1 or type 2) diabetes. However up to 5% diabetes in pregnancy may be a different subtype and only detected if atypical features are noted through careful history taking and examination.
Maturity Onset Diabetes of the Young (MODY) accounts for 1-2% of diabetes in the whole population. It is a heterogeneous group of disorders caused by mutations in genes important in beta cell development. The clinical course, complications as well as implications for pregnancy vary depending on the underlying molecular problem. MODY is often misclassified as type 1 or type 2 diabetes. Correctly identifying MODY has important implications for pregnancy as well as longterm surveillance and potentially for affected family members.
As it is recommended that all women (without pre-gestational diabetes) have their glucose tolerance assessed during pregnancy, this is a time when MODY may be first detected. Atypical features for type 1 (pancreatic autoantibodies absent, no history of ketoacidosis) or type 2 diabetes (lack of obesity, or metabolic syndrome features) and diabetes in 2 or more consecutive generations should prompt consideration of MODY.
GCK-MODY (MODY-2) accounts for 0.1% of diabetes in the general population but 1-2% of women with gestational diabetes. It leads to stable lifelong mild hyperglycaemia. Diagnosing GCK-MODY before or during pregnancy will alter the management approach in pregnancy with serial ultrasounds guiding the decision for commencement of insulin.
Sulphonylureas rather than insulin may be indicated if HNF1A (MODY-3) or HNF4A (MODY-1) is present.
Insulin is needed in women with HNF1B (MODY-5) which may be associated with renal or genital tract abnormalities. Metformin should be avoided in women with MIDD (‘‘maternal inherited diabetes and deafness’’) due to possible risk of lactic acidosis.