There is absolutely nothing in the OPs post to indicate he's trying to do anything but suit himself.
"She presented this as a done deal" Translation - Omg how dare a pregnant woman make decisions without asking my son because he fucked her!
"has had a transfer of office base for her job etc, wants to raise child where she grew up. She has lived in the same city as him for the decade he has known her." Translation - again - how dare she move out of the city he fucked her in!
"He is devastated as can't see how he can be an involved dad as he wanted to be now. " Translation - he doesn't want to move 2.5 hours away it's too much effort and he can't be arsed.
"He has signed up to driving lessons in quite a defeated way, reluctant to get legal advice as doesn't want to start things off badly." Translation - he can't even drive and is trying to pretend that's her problem and also sulking because he's going to have to do what most adults do and leave his public transport/walking bubble.
All this plus she's asking if a pregnant woman can be forced to stay put to suit her son 😆
It's nothing to do with 'but de fEmInIsMz!"
The pregnant woman is exercising her basic human rights, the OP wants to enable her lazy son so he won't have to inconvenience himself to be part of his kid's life. This is irrefutable, based on the information we have been given. If there is more info, we don't know it, so can't comment on it.