Parents bring their preparenthood experiences into their family relationships, which may have a persistent impact on family dynamics. One such significant experience is infertility, often shared by both partners but differentially experienced by women and men. Using a prospective longitudinal study of adoptive parents with a history of infertility challenges who later adopted a child (N = 461, 91% White), we aimed to (a) examine the impact of preparenthood infertility distress on heterosexual couples' perceived marital instability trajectories in the 11 years of parenthood and (b) test whether social support from their partner and other sources would moderate the impact of infertility distress. Results revealed cubic curves of marital instability for mothers and fathers during parenthood, where marital instability increased from the child age of 9 months to 4-5 years, then decreased till 8-9 years, followed by another increase to 11 years. Mothers' preparenthood infertility distress predicted higher marital instability after child age of 4.5 years, and their satisfaction with partner support mitigated this association. No such effect was identified for fathers. Overall, results indicated that mothers' infertility distress experienced before becoming a parent of their adopted child serves as a risk factor for marital instability in the long term. Moreover, partner support is an important buffer against this risk. This study underscores the importance of considering parents' preparenthood personal history in later family functioning. Discussion elaborates on the differing results for women and men and the implications for future research and intervention. (PsycInfo Database Record (c) 2025 APA, all rights reserved).