Aims/hypothesis <p>We aimed to examine offspring adiposity trajectories from birth to age 9–14 years and to assess the joint associations of maternal overweight and gestational diabetes mellitus (GDM) with these trajectories.</p> Methods <p>This is a prospective cohort study with 564 mother–child dyads from the Hyperglycemia and Adverse Pregnancy Outcome study Hong Kong field centre. Assessments and anthropometric measurements were taken during pregnancy, at delivery and at median ages of 7 and 10 years postpartum. Offspring adiposity was primarily assessed using sum of skinfold thickness. We used linear mixed-effect models to evaluate the independent and joint associations of maternal overweight and GDM with the offspring adiposity trajectories, and applied group-based trajectory modelling to identify distinct patterns of adiposity development based on both statistical indices and clinical interpretability.</p> Results <p>Offspring skinfold thickness trajectories varied significantly based on maternal overweight and GDM (<i>p</i>&lt;0.05). Group-based trajectory modelling identified two trajectory groups for skinfold thickness: 52.1% with slow increase and 47.9% with rapid increase. Combined maternal overweight and GDM was associated with 6.90-fold increased risk (95% CI 1.89, 33.32; <i>p</i>=0.006) of the rapidly increasing trajectory. Linear mixed-effect model analysis showed greater increases in skinfold thickness among offspring of mothers with either condition, with the highest trajectory observed in offspring of mothers with both conditions (β 1.62; 95% CI 0.69, 2.54; <i>p</i>=0.001).</p> Conclusions/interpretation <p>Maternal overweight and GDM are independently and jointly associated with rapidly increasing adiposity trajectories from birth to early adolescence. The findings underscore the importance of considering both maternal metabolic conditions when evaluating offspring adiposity risk.</p> Graphical Abstract <p></p>