The literature emphasizes that motivations for having a child are an important factor in mother-child adaptation post-adoption. Unfortunately, there are no instruments on motivations to have a child adapted to this population that can contribute to new evidence with quantitative research. Therefore, this paper aimed to adapt and investigate evidence of validity and reliability of the MCS scale (Brenning et al.,
2015) within a sample of expectant adoptive mothers. The transcultural adaptation followed eight rigorous steps, including experts, focus groups, back-translation, and a pilot study conducted with biological mothers and soon-to-be adoptive mothers. For evidence of reliability, the scale was applied to a sample of 267 women waiting to adopt a child, with an average age of 38.7 years. The five-factor structure was confirmed, and the factors correlated as in a continuum, supporting the Self-Determination Theory. The MCS is valid and reliable for assessing the quality and intensity of the motivation to have a child in Brazil and in the context of adoptive motherhood, and it is suitable for future empirical research and practical application.