Background: The perinatal period precipitates significant intra- and inter- personal changes. How heterosexual couples understand and account for such changes, however, has received relatively little attention. Methods: Semi-structured individual interviews were undertaken as part of a longitudinal study on planned first-time parenthood. This article reports on an inductive thematic analysis of a data corpus focused on six interview questions (three from interviews conducted during pregnancy, and three from interviews conducted six months after the birth of the child), derived from interviews with eight individuals (4 women and 4 men) comprising four couples. Results: In antenatal interviews, the theme of intrapersonal changes differentiated participants by two sub-themes that were then linked to postpartum experiences. Those who 'prepared for the worst' reported positive experiences after the arrival of a child, whilst participants who during pregnancy viewed life after the arrival of a child as 'an unknown' experienced challenges. Similarly in terms of the theme of interpersonal change, antenatal interviews were linked to postpartum experiences by two sub-themes, such that participants who approached the impending arrival of a child as a team effort reported that the arrival of a child cemented their relationship, whilst participants who expected that the couple relationship would buffer child-related stressors experienced challenges. Conclusions: Findings highlight the importance of a focus in antenatal education on the psychological effects of new parenthood, and support for the couple relationship during the perinatal period.