PURPOSE: Although congenital heart defects (CHD) are a fatal disease in newborn infants, little is known whether and to what degree they affect mental health of parents. METHODS: This cohort study includes parents who were free of depression when their children were first diagnosed with CHD between 2016 and 2021 in Japan. Each parent was matched in a 1:1 ratio using age, gender, income, and the birth date of the infant. Pooled logistic regression was applied to estimate the time-varying risks of parents' depression associated with their infants' CHD over 3 years of follow-up. RESULTS: Among 4520 matched parents, a new onset of depression was observed in 99 individuals (2.2 %). During the follow-up period of three years, the risk difference (RD) for parents' depression between exposed and unexposed groups was at its highest around 12 months but then dwindled afterward (6 months: RD [95 % confidence interval] = +0.66 [0.33, 1.01]
12 months: RD = +0.81 [0.35, 1.30]
24 months: RD = +0.25 [-0.47, 0.99]
and 36 months: RD = -0.36 [-1.27, 0.56]). Our negative control outcome analysis showed no difference in the incidence of diabetes diagnosis by exposure status. CONCLUSION: Newborn infants' CHD event was associated with an elevated risk of depression in parents. Our findings highlight the importance of support for informal caregiving and preventive psychological care for parents whose newborn infants developed CHD.