History and exam
Key diagnostic factors
common
presence of risk factors (usually asymptomatic)
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 GDM.
Risk factors
strong
elevated BMI
previous macrosomic baby
Having a previous baby that weighed ≥4.5 kg is associated with a significantly higher risk of being diagnosed with 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][24] Hypothesised mechanisms include the ‘thrifty gene’ hypothesis.[18][25] Interestingly, the association with GDM is strongest when there is a maternal family history, leading to speculation that intrauterine factors and mitochondrial DNA may play a role.
non-white ancestry
Associated with increased risk of GDM.[15][26][24] 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 GDM rises gradually until the age of 40, after which it increases more sharply, meaning the overall likelihood of GDM is doubled in women over the age of 40.[24] 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 GDM risk.[19] Also associated with type 2 diabetes, and even in the absence of pregnancy, women with this syndrome should be considered for screening of glucose and lipid abnormalities.[20]
A meta-analysis of studies comparing pregnancy outcomes between women with PCOS and those without diagnosed PCOS found statistically significant increased rates of GDM, pregnancy-induced hypertension, pre-eclampsia, preterm delivery, and small-for-gestational-age infants in women with PCOS.[27]
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