At the end I looked over at the midwife's computer screen.
In the section for my personal details, there were boxes for "Legal sex" and "Sex assigned at birth". Fine. Seems like comprehensive data collection.
Except that my "sex assigned at birth" was left blank. As this was a maternity appointment, the answer to this question is self-evident. No reason for it to be left blank.
And my "legal sex" was filled in as female. She didn't ask me my legal sex, and had no way of knowing if I had a GRC.
My midwife was very nice. She also spoke English as a second language. So I guess this goes in the new ONS bucket of opaque questions leading to poor data collection from the large section of the population that does not speak genderwang.