Background: Evidence shows that pregnancy and early postpartum periods are crucial to the development of the mother–baby relationship. Objective: The aim of this study was to evaluate the impact of common mental disorders (CMD) during pregnancy on child’s mental development during the first year. A prospective study was carried out with 204 pregnant women in the third trimester of pregnancy and continuing with their babies to 3.5 and 12 months of age. Method: To assess the presence of CMD, the Brief Symptom Inventory and the Inventory of the Clinical Evaluation of Depression were used. Evaluation of the babies’ mental development and the socio-emotional state was carried out using the Griffiths Mental Scale (0–2) and the Brief Infant Toddler Social and Emotional Assessment (BITSEA). Results: We observed 20 babies born to women with a positive diagnosis for CMD and who presented a positive screen in the BITSEA. We also observed a statistically significant relationship regarding the diminished development in certain Griffith’s subscales of babies whose mothers showed presence of psychotic, anxiety, hostility and depressive symptoms during pregnancy. Conclusion: We conclude that the presence of CMD influences the mental, social and emotional development levels of infants in their first year. Less