The objective was to explore the preliminary functioning of a self-report questionnaire designed to assess parental reflective functioning (PRFQ, Luyten et al., 2009, unpublished manual) during early postnatal phase and with a large population-based sample. Parental reflective functioning (PRF) refers to parental capacity to focus on experience and feelings, within self, in the child and underlying observed reactions. Individual differences in PRF reportedly affect child attachment and socio-emotional development. Cost-effective tools to assess key areas of early parenting are needed for both research and clinical purposes. The factor structure of a 36-item version suitable for early postnatal phase was explored using population-based data from the Finn Brain Birth Cohort Study (425 mothers and 237 fathers). Exploratory and confirmatory factor analysis resulted in a 14-item version comprising four factors capturing relevant aspects of early PRF. The factor structure was further tested with separate participants from the cohort (1030 mothers and 422 fathers). Mothers tended to score higher than fathers in PRF. Among mothers, parity, age, and financial situation were associated with postnatal mentalization. Level of education was associated with postnatal mentalization in both genders. The 14-item PRFQ-Fi has potential to serve as a new screening tool for very early parenting.