I don't think the midwives are objecting to training about supporting mothers-to-be with a trans history, as such. I'd wager some solid, evidence-based resources on how to deal with mothers with a history of taking testosterone / have had mastectomies etc - and their babies - etc could be welcome.
They're objecting because this training is bollocks - it's more ideological nonsense from lobby groups - showing they haven't learned this isn't a good idea after GIDS.
The training is based on a shonky piece of "research" (not peer-reviewed and absolutely pulled apart in that letter).
It recommends exactly the kind of thing you'd expect the ideologues to say - e.g. to "introduce gender inclusive (de-sexed) language for all maternity service users" and has nothing useful to say about actually caring for pregnant women with a trans history.
It's bollocks. It's about pushing an ideology - and ironically, that ideology doesn't even help those it claims to!