Last night I got triplets for one family (and the trophy). I used a twin from the previous generation. She had fertility problems, so I gave her baby boost. She had triplets on the first try! This family had two sets of twins in the first generation as well.

I haven't had so many problems getting triplets as twins. If there are going to be multiples, 90% of the time they are triplets. They are still extremely rare, but they tend to be triplets.