Maternal Gestational Diabetes and Trajectories of Offspring Fat–Lean Balance in the Millennium Cohort Study

Aims We aimed to examine whether offspring exposed to maternal gestational diabetes mellitus (GDM) had different fat–lean balance trajectories from unexposed offspring and whether the estimated associations were attenuated after adjustment for maternal pre‐pregnancy adiposity. Methods Using UK Millennium Cohort Study data, we analysed body composition outcomes, including fat mass (FM), body fat percentage (BF%), fat mass index (FMI), fat‐free mass index (FFMI), and the FMI/FFMI ratio. Linear mixed‐effects models characterised body composition trajectories from ages 7–17 years, with additional adjustment to assess the attenuation of the estimates after accounting for maternal pre‐pregnancy adiposity. Results The analysis included 14 329 offspring, of whom 170 were exposed to maternal GDM. In the primary adjusted model, GDM‐exposed offspring had higher model‐predicted values for all body composition indices than unexposed offspring across the observed ages. GDM‐by‐age interaction terms indicated age‐varying between‐group differences for FM, FMI, and the FMI/FFMI ratio (all p < 0.05), with borderline evidence for BF% ( p = 0.050) and no clear evidence for FFMI. After additional adjustment for maternal pre‐pregnancy adiposity, the estimated between‐group differences were attenuated, and some age‐specific contrasts, particularly at age 7 years, were no longer statistically significant. Nevertheless, age‐varying between‐group patterns remained evident for several body composition indices. Conclusion Maternal GDM exposure was associated with age‐varying differences in offspring fat mass and fat–lean balance during childhood and adolescence, and these associations were attenuated after adjustment for maternal pre‐pregnancy adiposity.