Child overweight remains a prevalent public health concern, but the impact of maternal psychosocial stress and related constructs, the timing, and possible trajectories on child body mass index (BMI) is controversial. We aimed to investigate the association of maternal stress, depression and anxiety symptoms, and maternal hair cortisol concentrations (HCC) at delivery, 6, and 12 months postpartum with child BMI and age- and sex-standardized BMI (BMI-SDS) at age 3 years. Data were derived from the Ulm SPATZ Health Study with a baseline examination between 04/2012 and 05/2013 at the University Medical Centre Ulm, Germany, the only maternity clinic in Ulm, with a good representation of the source population. Adjusted regression analyses based on BMI/BMI-SDS (dependent) and trajectories of stress, depression, and anxiety (independent variables) were investigated in 596 mothers and children. Multiple imputation of missing covariates was performed. Various trajectories in independent variables were identified, trajectories of maternal anxiety symptom differed between child sexes. We did not find an association between trajectories of maternal chronic stress, depression symptoms, or HCC and child BMI/BMI-SDS. However, trajectories of low-increasing maternal anxiety symptoms were linked to higher child BMI compared to a low-stable trajectory group (b = 0.58 kg/m , 95% Confidence Interval: 0.11; 1.04) in girls. Trajectories of maternal anxiety symptoms were associated with the child's BMI/BMI-SDS in girls at age 3 years. However, further large scale studies should include variables to determine the causal pathway and enlighten sex-specific differences.