I'm not sure it is off track, as rules about who should be able to have terminations and when they can be carried out are all part of the original debate. It is not something that exists in a vacuum.
Jane's point about the financial considerations of disability is a good one, as is the impact of having a profoundly disabled child on a family's experience and life chances, and also the life chances of th disabled child should be considered. There are also cultural and religious beliefs about the sanctity of life, of taking responsibility for one's actions and so on, which are not universally held. I realise that all laws are based on that sort of thing (and much UK law is based on Christianity) but there is a difference between making murder or robbery illegal and terminating a pregnancy, unless you take the view that when a foetus is viable then abortion is murder. That is a debatable viewpoint, and although I share it up to a point I don't feel that it should be imposed on others. Also, if we decriminalised murder, we would all be at risk of being killed, but legalised abortion only affects the people concerned. I don't know if risk of being affected by a crime should be taken into account when legislating against it, but maybe that needs to be part of the debate too.
There is no reason why we couldn't pour more resources into supporting women who resist pressure to terminate female pregnancies, and into educating younger generations about sex equality and respect for women. I think that would be a good thing to do if there is a genuine problem in this area (I'd like to see the figures, though, as well as how they show that sex was the reason for the decision to terminate).
I am in no way arguing that aborting girls is a good thing, but how can we have a rule that allows termination based on mental health of the mother and simultaneously refuse a women who is afraid of ill-treatment if she carries a female baby to term? That is a contradiction, isn't it?