Postnatal testosterone levels and disorder relevant behavior in the second year of life

The objective of the current study was to investigate the relationship between testosterone collected at 3-4 months of age and sex-linked disorder-relevant behaviors in the second year of life. Eighty-four children participated at 3-4 (when salivary testosterone levels were obtained and second to fourth digit ratios were measured) and 18-24 months of age (when behavioral ratings of aggression and verbal ability were coded from two 8-min play sessions). Parents also completed the Brief Infant-Toddler Social and Emotional Assessment, and the four subscales (Internalizing, Externalizing, Dysregulation, and Autism Spectrum Disorder) were used to indicate child specific problems. Greater postnatal testosterone levels in early infancy were predictive of more male-typical behaviors in the second year of life (i.e., more autism spectrum behaviors, less time vocalizing, and more Internalizing Problems). These results support the hypothesis that early infancy may be another critical period for the development of gender-linked behavior.