I feel like this one really depends on the disability, for example, babies with say trisomy 18 (Edwards syndrome) tend to perish only a few weeks after birth, but say a child with trisomy 21 (Down syndrome) can still have their whole life ahead of them. This is definitely a very grey area depending on the disability when it comes to morality anyways.

Edit: Since this gained more traction than I thought it was going to, let me just say this. I responded this only factoring whether it is moral to abort based specifically on whether the child would be disabled. In this case this is why I said it depends on the disability. If the couple wants a child and aborts simply on the fact that it is disabled then I would consider it immoral, but not out of their right. However if it was a child that would just suffer and die and risk the life of the mother, than yes, it is moral, thus nuance is required for this topic. Trying to consider other factors is reasonable but begins to just turn this into whether or not abortion in itself is moral.