Actually, this is what is said
A large majority of people that have been pregnant or have given birth identify as women. We can include intersex men and transmen who may get pregnant by saying ‘pregnant people’ instead of ‘expectant mothers’.
There is no indication that this is what is supposed to be said only to intersex or FtMs F-2-F. It is very general advice and gives the impression it should be used generally, for example in policy, advice pamphlets or even to pregnant women (like 99.999999999999999% of those who get pregnant). In fact, the document says
"This guidance should be applied to all forms of communication, including conversations, committee papers, documents, letters, emails and the website. Anything that we produce reflects the association and it is vital that all our communications are free from discriminatory language, or what could be interpreted as discriminatory language. Using our values and behaviours as the foundation, inclusive language does not discriminate against
anyone on the basis of any of the protected characteristics in the Equality Act 2010"
Thus, it is general advice.