Interesting about the gender question. Maybe there isn't much difference between 'can't cope if I have another girl' and 'can't cope with a child with special needs' at the individual level (although there is still a difference, all the same, it's not the same). Big difference at the level of society though if you end up with a very skewed population of 70:30 boys to girls, say. It really, really shows, whereas fewer disabled people doesn't show as much. There are societies where cultural expectations make having daughters cripplingly expensive. There are societies in which it's difficult or impossible to get even a fraction of the support and help someone might need if born disabled. Either or those things can make people think long and hard, and try to put emotion aside, and decide to terminate pregnancies they would really prefer to go on with. Neither may be what any of us really want to happen. But if you don't believe abortion is murder, you won't see it as murder either way.
You can't really debate this without agreeing about the abortion issue in general though. There are different attitudes - if you take the similar situation of people choosing embryos for implantation with IVF, while knowing something about genetic diseases they may have, you have two main attitudes:
(1) People who see selecting only the embryos without the disability as removing the disability from their next child - i.e. are imagining the same child, with and without the disability, and feel they're taking the disability away.
(2) People who see selecting only the embryos without the disability as choosing only some potential next children as worth being given a chance of life, while leaving the potential children with disabilities to wait forever and never get through to the world, even though they too could have good lives.
If you see it the first way it seems mad not to try to remove the disability - if you see it the first way you see anything else almost as inflicting the disability on the child. If you see it the second way, you tend to see it more as giving the children whose genetic mix has given them a disability a chance of life, rather than keeping them back in the foyer and never letting a child with that kind of mix get all the way into the world. You're seeing several potential next children, some with disabilities, some without, any one of whom may be the next child, rather than one 'next child', who may or may not have this disability inflicted on them.
Those different attitudes are significant but they're still not all there is when it comes to people deciding to terminate. I have a congenital disability and I tend to see things the second way much more clearly than the first. BUT I still, separately, would be thinking about whether I could cope if I knew a child with a disability was on the way - could I cope physically, emotionally, could my marriage cope, all of that stuff I'd be thinking about coldly, practically, and I simply could not rule out terminating (early) on those grounds. That doesn't mean I think everyone should or that I think disabled children don't have lives worth living. But I have lots and lots of potential children I could be conceiving, as well as any already conceived, and not all will be born. It would be hard to terminate any pregnancy, really harsh and difficult, but I can imagine circumstances in which I would do it, even while knowing that other people with superficially similar circumstances might make other decisions.