ROME — The Vatican on Monday flatly rejected what it cast as the notion that individuals can choose their gender, releasing its first extensive document on the issue as Western countries are increasingly wrestling with the social and legal implications of more fluid definitions of identity.

The document, issued by the Vatican department overseeing Catholic education, echoed past statements by Pope Francis. It argued that acceptance of flexible ideas of gender posed a threat to traditional families and ignored the natural differences between men and women.

It lamented “calls for public recognition of the right to choose one’s gender, and of a plurality of new types of unions, in direct contradiction of the model of marriage as being between one man and one woman, which is portrayed as a vestige of patriarchal societies.”

The idea of gender moving along a spectrum was “nothing more than a confused concept of freedom in the realm of feelings and wants.”