We’ve looked at user research, including the work of colleagues at the Office for National Statistics. We decided to use the phrase “sex assigned at birth” when we’re talking about trans health and gender dysphoria, as this is the language our audience uses.
In other cases, we use “the sex someone was registered with at birth” because user research shows that most people understand this better as it refers to an actual event.
We also had a lot of feedback about the terms “intersex” and “differences of sex development” (DSD). Some people prefer one term, some the other. We’ve made this clear in our guidance and we recommend, as always, that teams test their language with the people who’ll be using their content or service.
We’ve just published another update to our page on inclusive language. The guidance there should help you get started but, when you do your user research, you may find that something else works better. There is no one right answer. Please let us know what you find.