The purpose of the present study was to examine vulnerability factors in expecting parents that might lead to mental illness in the perinatal period. Specifically, we studied how parental early adversity, attentional bias to infant faces, repetitive negative thinking, and demographic factors, were associated with pre- and postnatal depressive symptoms and parenting stress. Participants were expecting parents taking part in the Northern Babies Longitudinal Study, where assessments were made both pre- and postnatally. Assessments included both questionnaires and cognitive tasks. About half of the participants received the Newborn Behavior Observation (NBO)-intervention after birth, between pre- and postnatal assessments. Results show that repetitive negative thinking was a significant predictor of both depressive symptoms and parenting stress, while education, social support, and parity came out as protective factors, especially in mothers. Parental early adversity had an indirect effect on postnatal depressive symptoms and parenting stress, mediated by prenatal and postnatal depressive symptoms, respectively. The NBO intervention did not affect the results, signifying the importance of early childhood adverse events and negative thinking on parents' postnatal adjustment and mood, even when an intervention is provided. In conclusion, repetitive negative thinking is a significant vulnerability factor independent of the presence of depressive symptoms, and health professionals must be aware of parents’ thinking style both during pregnancy and after birth.