[Formula: see text] Sex differences in neurodevelopment trajectories over the first 3 years

This study aimed to examine sex-specific neurodevelopment trajectories and associated factors for providing a reference for sex-specific neurodevelopment assessment and early targeted intervention. We hypothesized: 1) boys and girls have distinct neurodevelopment trajectories, in total or specific domains; 2) maternal and birth factors were associated with neurodevelopment trajectories differently between boys and girls. A retrospective cohort study was performed in children aged <3 years old, and neurodevelopment was assessed by trained medical staff using CNBS-R2016, a validated tool completed based on observation. Group-based trajectory modeling (GBTM) was used to identify the trajectories of neurodevelopment in boys and girls, respectively. Using GBTM, "persistently high - quickly rising," "persistently high - slowly rising," "persistently low - falling" trajectories were documented in girls, and "persistently high - slowly rising," "persistently low - stable" trajectory was revealed in boys. For girls, totally (92.7%) were in the high development trajectories, compared to 52.6% for boys. In the low development trajectories, there was a higher proportion of boys than girls (47.4% vs. 7.3%), although a falling trend was identified for girls. The trajectories for each domain of neurodevelopment also showed sex-dependent variations, with the adaptivity domain primarily driving total development trajectories in girls, and the language domain in boys. In multinomial regression analysis, gravidity and non-breastfeeding were associated with increased risks of having low development trajectories for both boys and girls. Among girls, preterm birth was also associated with low development trajectory. The findings may have implications for sex-specific neurodevelopment screening and interventions during early childhood.