Psychiatric illness can pose serious risks to pregnant and postpartum women and their infants. There is a need for screening tools that can identify women at risk for postpartum psychosis, the most dangerous perinatal psychiatric illness. This study used exploratory factor analysis (EFA) and Rasch item response theory (IRT) models to evaluate the psychometric properties and construct validity of the Spanish language version of the 16-item Prodromal Questionnaire (PQ-16) as a screening tool for psychosis in a population of pregnant Peruvian women. The EFA yielded a four-factor model, which accounted for 44% of the variance. Factor 1, representing “unstable sense of self,” accounted for 22.1% of the total variance; factor 2, representing “ideas of reference/paranoia,” for 8.4%; factor 3, representing “sensitivity to sensory experiences,” accounted for 7.2%; and factor 4, possibly representing negative symptoms, accounted for 6.3%. Rasch IRT analysis found that all of the items fit the model. These findings support the construct validity of the PQ-16 in this pregnant Peruvian population. Also, further research is needed to establish definitive psychiatric diagnoses to determine the predictive power of the PQ-16 as a screening tool.