Background: Gestational weight gain (GWG) has been shown to be a risk factor for overweight in offspring. Aim of this study was to quantify the contributions of trimester-specific and total GWG on offspring's BMI and waist circumference (WC). This is of interest for the design of interventions targeted at women showing a high GWG in early pregnancy. Methods: In a retrospective cohort study data on GWG (total and by trimester, exposure), a number of potential confounders, and children's BMI z-scores and WC (outcomes) were analyzed using structural equation models to disentangle the trimester-specific direct effects of GWG and indirect effects mediated via total GWG. Results: 7313 mother child pairs with a children's mean age of 5.81 years were analyzed. Total effects (indirect + direct) of GWG (kg/week) on children's BMI z-score and WC (cm) were observed in all trimesters, most prominently in the second. The longitudinal effect of GWG is a composite of trimester-specific direct effects (on BMI: 0.105, 0.255, 0.002, on WC: 0.538, 1.64, 0.308) and total GWG (on BMI 0.608, on WC: 1.03) at the end of pregnancy. Conclusions: Both trimester-specific priming and total GWG explained offspring's anthropometrics. The results indicate, that reversal from additional weight gain attained early in pregnancy resulting in normal total GWG at the end of pregnancy might still contribute to a substantial reduction of offspring's BMI and WC.