Gestational diabetes mellitus

Gestational diabetes is defined as any degree of glucose intolerance with onset or first recognition during pregnancy. GDM often precedes a diagnosis of T2DM, occasionally it is a new presentation of T1DM. Management includes a combination of diet, metformin and insulin therapy.

Is the patient asymptomatic?

In many centres, GDM is screened for in pre-defined risk groups of pregnant women by performing an OGTT and it will therefore be discovered at a pre-symptomatic stage.

Common criteria for performing screening for OGTT are: advanced maternal age, history of previous macrosomia, maternal obesity and persistent glycosuria.

Is there a history of macrosomia or obstructed labour in previous pregnancies?

GDM has a high risk of recurrence in subsequent pregnancies. Even if it has not been formally diagnosed previously, suspicious features such as macrosomia and shoulder dystocia in previous pregnancies should alert the physician to the possibility of previous undiagnosed GDM.

Is there a history of GDM in previous pregnancies?

GDM has a high risk if recurrence in subsequent pregnancies.

Has the patient been drinking more water and passing more urine than usual?

Polyuria and polydipsia are the cardinal symptoms of diabetes and occur when the blood glucose level exceeds the renal threshold for glucose excretion - usually approximately 10 mmol/L.

GDM sometimes presents in this manner. It is also possible for T1DM to present during pregnancy which will often be associated with a more symptomatic presentation.

However, the commonest presentation of GDM is asymptomatic, screen-detected.

Has the patient noticed a change in eye sight - particularly an inability to focus?

Variable difficulty with focusing - that has been present for only a short period and may be fluctuating - is due to osmotically driven swelling of the lens and varies as the degree of hyperglcaemia varies.

However, it is less usual for GDM to present with full blown osmotic features.

Has the patient experienced generalised pruritis, or oro-gential thrush?

These symptoms can be common in pregnancy and often arise due to causes other than diabetes, but are still worth enquiring about and recording.

Has the patient any other relatives with diabetes?

A thorough family history is essential to detect monogenic causes of diabetes such as MODY and mitochondrial diabetes

Type 2 and gestational diabetes often run quite strongly in families.

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