Data from a multi-method, longitudinal study involving a community sample (N = 120) of pregnant women aged 18–42 were used to examine disrupted maternal representations of the child as a mechanism of the transmission of trauma from mother to infant. Using structural equation modeling, the best fitting model indicated that severity of mothers’ childhood interpersonal trauma was associated with severity of disruption in prenatal representations of the child, which in turn was associated with less secure infant-mother attachment at 1 year of age. There was a significant indirect effect of maternal childhood interpersonal trauma on infant-mother attachment insecurity via disrupted prenatal maternal representations. Findings highlight an important mechanism of trauma transmission that could be targeted in interventions with mother-infant dyads.