The arrival of a new child brings joy and purpose, yet it is also a pivotal life event that can significantly impact parents' mental health and couple functioning. Although parental mental health has garnered increasing empirical attention, further research is warranted to document the psychological and relational adjustment of both mothers and fathers across the postpartum period and into early parenthood. The Parental Couples Project is a longitudinal cohort study examining how psychological well-being and couple adjustment evolve over time after the birth of a new child. As part of this project, the current presentation draws on data from 1,142 parental couples randomly selected across the province of Quebec through a partnership with the provincial Parental Insurance Plan. Both mothers and fathers were assessed across four waves spanning 30 months (child's age at T1: 3 months; T2: 9 months; T3: 18 months; T4: 30 months) using validated self-report measures of parenting stress, psychological distress, postpartum depression, and life, relationship, and sexual satisfaction. Two-way repeated ANOVAs revealed significant gender differences at all timepoints: Mothers consistently reported higher levels of postpartum depression and psychological distress, while fathers reported higher parenting stress and lower life satisfaction. In terms of relational outcomes, mothers reported greater relationship satisfaction, while fathers reported greater sexual satisfaction. Significant time effects were also observed, with both parents reporting increased parenting stress and declines in life, relationship and sexual satisfaction over time. Notably, the proportion of parents meeting criteria for clinically significant relationship distress nearly tripled from T1 to T4 (mothers: 5.2% to 15.4%; fathers: 5.4% to 17.1%). No gender x time interactions were found. These findings highlight the evolving nature of well-being during early parenthood and support the need for tailored strategies to address the distinct challenges faced by both parents through this critical period.