Other authors (_e.g._, the indispensable [Anne Lawrence](http://www.annelawrence.com/)) use "natal sex", but that has the opposite problem: "natal" (of or relating to birth) could be too generous about the extent the extent to which HRT and surgeries actually change someone's sex. (Talking about the _historical_ fact of someone's sex at birth might suggest that it's been successfully changed since.)
My proposal: "developmental sex" (in the sense of [developmental biology](https://en.wiktionary.org/wiki/developmental_biology), "the study of the physiological changes that occur within individual organisms from their conception through reaching physical maturity"). Trans men (respectively women, _&c._) weren't only _born_ female; their bodies went through the female developmental trajectory until they transitioned. Hopefully this alternative solves all the problems and will help us communicate more clearly!
Other authors (_e.g._, the indispensable [Anne Lawrence](http://www.annelawrence.com/)) use "natal sex", but that has the opposite problem: "natal" (of or relating to birth) could be too generous about the extent the extent to which HRT and surgeries actually change someone's sex. (Talking about the _historical_ fact of someone's sex at birth might suggest that it's been successfully changed since.)
My proposal: "developmental sex" (in the sense of [developmental biology](https://en.wiktionary.org/wiki/developmental_biology), "the study of the physiological changes that occur within individual organisms from their conception through reaching physical maturity"). Trans men (respectively women, _&c._) weren't only _born_ female; their bodies went through the female developmental trajectory until they transitioned. Hopefully this alternative solves all the problems and will help us communicate more clearly!