You can only abort the pregnancy if there is a vital danger for the mother in order to sacrifice one life instead of two. Otherwise, the abortion has no difference than killing a born child.
It is also not right to end the life of a fetus for predicted health problems like a disability of the child. The reliability of genetics science and the method of ultrasonography is controversial in this issue. There have been cases of wrong predictions and it has been observed that some fetuses were born quite healthy for whom the predictions of disability or vital risks had been made.
It would not matter even if we definitely knew that the child will be disabled, because it is unlawful to kill a man just because he is disabled.