History and exam

Key diagnostic factors

common

presence of risk factors (usually asymptomatic)

Gestational diabetes mellitus (GDM) is usually asymptomatic. Key risk factors include elevated BMI, previous gestational diabetes, previous macrosomic baby, non-white ancestry, family history of diabetes mellitus, and advanced maternal age (>40 years). Another risk factor that may contribute is polycystic ovarian syndrome.

Other diagnostic factors

uncommon

polyuria

May be a sign of overt hyperglycaemia. Suggests uncontrolled diabetes and urgent need for plasma glucose testing.

polydipsia

May be a sign of overt hyperglycaemia. Suggests uncontrolled diabetes and urgent need for plasma glucose testing.

fetal macrosomia in a previous pregnancy

Prior birth of an infant >4.5 kg may be due to unrecognised gestational diabetes mellitus (GDM).

Risk factors

strong

elevated BMI

Obesity is a strong predictor of gestational diabetes mellitus (GDM).[4][15][16][27]​​​ Risk is almost tripled when BMI is >30 kg/m².[4][28]​ Obesity leads to increased insulin resistance, which is further compounded by pregnancy.

previous gestational diabetes

Gestational diabetes mellitus (GDM) recurs in 30% to 84% of subsequent pregnancies.[4]​[17]​​

previous macrosomic baby

Having a previous baby that weighed ≥4.5 kg is associated with a significantly higher risk of being diagnosed with gestational diabetes mellitus (GDM) in a subsequent pregnancy (OR 5.59, 95% CI 2.68 to 11.7).[4]

family history of diabetes mellitus

Family history of type 2 diabetes increases risk; the relative risk was 1.68 in a large prospective study.[4][28] Many candidate genes have been identified, although not all the results are conclusive and they require further investigation.[29]

non-white ancestry

Associated with increased risk of gestational diabetes mellitus (GDM).[15][28]​​[30]​​​​ In the UK, National Institute for Health and Care Excellence guidelines recommend screening women who have a family origin from an area with high prevalence of diabetes (e.g., South Asian, black Caribbean, or Middle Eastern women).[4] Environmental and social factors are potential contributors to disparities in diabetes prevalence and disease outcome.[18]

advanced maternal age (>40 years)

The risk of gestational diabetes mellitus (GDM) rises gradually until the age of 40, after which it increases more sharply and likelihood of GDM is more than doubled.[28][31]​​ This mirrors the increasing prevalence of type 2 diabetes seen with increasing age, and is thought to arise from decreasing pancreatic beta-cell reserve in the setting of increased insulin resistance.[15]

polycystic ovarian syndrome (PCOS)

Associated with insulin resistance and obesity.[15] This syndrome more than doubles gestational diabetes mellitus (GDM) risk.[19] It is also associated with type 2 diabetes; even in the absence of pregnancy, screening of glucose and lipid abnormalities should be considered in women with PCOS.[20]

A meta-analysis of studies comparing pregnancy outcomes between women with diagnosed PCOS and those without the condition found statistically significant increased rates of GDM, pregnancy-induced hypertension, pre-eclampsia, preterm delivery, and small-for-gestational-age infants in women with PCOS.[32]

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