Early‐Onset Versus Late‐Onset Gestational Diabetes Mellitus: A Systematic Review and Meta‐Analysis of Maternal, Perinatal and Neonatal Outcomes

Aim To determine the precise relationship between the timing of gestational diabetes mellitus (GDM) diagnosis and adverse maternal, perinatal and neonatal outcomes. Materials and Methods PubMed, EMBASE, Cochrane Central, Web of Science and CINAHL from inception to March 5, 2026 were systematically searched for observational studies and post hoc analyses or subanalyses of randomised controlled trials comparing outcomes between early‐onset GDM (eGDM) and late‐onset GDM (LGDM). The tested outcomes included insulin initiation, caesarean delivery, preterm birth, large‐for‐gestational‐age (LGA) infants and neonatal intensive care unit (NICU) admission. Pooled odds ratios (ORs) were calculated using random‐effects models. Heterogeneity was assessed using Cochran's Q test and I 2 statistic. Meta‐regression and subgroup analyses were used to explore the sources of heterogeneity and sensitivity analyses confirmed robustness. The protocol was registered in PROSPERO (CRD420261328602). Results Thirty‐five studies encompassing 105 123 pregnancies met inclusion criteria. eGDM is associated with significantly elevated odds of insulin initiation (OR, 95% CI: 2.26, 1.75–2.91), caesarean delivery (1.16, 1.01–1.33), preterm birth (1.32, 1.05–1.64), LGA (1.29, 1.06–1.58) and NICU admission (1.24, 1.03–1.50). Heterogeneity is substantial ( I 2 = 57.3%–86.5%). Certainty is rated by GRADE as moderate for preterm birth and low for the other four outcomes. Conclusions eGDM versus LGDM is associated with higher risks of adverse outcomes, particularly insulin initiation. Gestational age at diagnosis may serve as a key risk stratifier, highlighting the need for risk‐stratified approaches rather than universal early surveillance. Future research should prioritise individual‐participant data meta‐analyses and randomised trials of tailored protocols.