Semantics

Something I've often wondered about...

Say you're pregnant with multiples. Let's say, oh, quints - hypothetically, of course.

If you lose two, during pregnancy or after birth, you are encouraged to call them "surviving quints". They are, after all.

If you instead decide to kill two - reduce, or "send them to God early" so to speak - it then becomes a triplet pregnancy.

Why is that? I really want to know.