Assessing the independent and combined impact of obesity and gestational diabetes mellitus on adverse maternal outcomes: A systematic review and meta‐analysis

Aims To evaluate the impact of obesity, with or without gestational diabetes mellitus (GDM), on adverse maternal outcomes and determine whether the combination of obesity and GDM confers a greater risk compared to obesity alone. Methods We systematically searched MEDLINE, EMBASE, Scopus, CINAHL and the WoS Core Collection, identifying 19 studies. Pooled estimates (odds ratios, OR and mean differences, MD) with 95% confidence intervals (CI) were calculated using random effects models. Results Obesity alone significantly increased the risk of caesarean section (OR 2.63, 95% CI 1.40–4.94), pre‐eclampsia (OR 3.09, 95% CI 2.35–4.07), induction of labour (OR 1.73, 95% CI 1.58–1.90) and postpartum haemorrhage (OR 1.35, 95% CI 1.01–1.81) compared to normal‐weight, non‐GDM women. GDM alone also increased the risk of caesarean section (OR 1.66, 95% CI 1.28–2.15) and pre‐eclampsia (OR 1.57, 95% CI 1.21–2.04), though to a lesser extent. Combined, obesity and GDM markedly elevated risks, with a four‐fold increase in caesarean section (OR 4.26, 95% CI 1.57–11.53) and pre‐eclampsia (OR 4.07, 95% CI 2.90–5.71), and a sixfold increase for induction of labour (OR 6.44, 95% CI 1.25–24.63). Comparatively, obesity alone conferred a higher risk for caesarean section and pre‐eclampsia than GDM alone (OR 1.45, 95% CI 1.03–2.03 and OR 2.15, 95% CI 1.50–3.09, respectively). No significant differences were observed for instrumental delivery rates. Conclusions Obesity contributes significantly to adverse maternal outcomes, conferring a greater risk for caesarean section and pre‐eclampsia than GDM alone. The combination of obesity and GDM amplifies these risks, underscoring the need to prioritise obesity management as a distinct focus in pregnancy care.