Maternal perinatal stress is a well-documented risk factor for adverse child outcomes, but limited evidence is available from Latin America. This study investigated associations between maternal psychosocial stress during pregnancy and postpartum and infant socioaffective development at 3 months of age in Argentina. The sample included 198 mother-infant dyads recruited from two public health centers. Mothers completed standardized assessments of anxiety, depression, perceived stress, and pregnancy-specific distress during the second and third trimesters and 3 months postpartum. Infant socioemotional development and temperament were assessed at 3 months using parent-report instruments. Latent profile analysis identified three socioaffective profiles (Reactive, Moderate, Adapted). Multinomial logistic regressions showed that maternal stress--particularly during the second trimester--predicted profile membership. Higher prenatal and cumulative stress levels increased the odds of classification into the Reactive profile and decreased the likelihood of classification into the Adapted profile. These findings underscore the developmental impact of maternal stress and highlight the importance of early detection and intervention in prenatal care, especially in low- and middle-income contexts.