First off: the premise of this is definitely absurd - actors are people with families first, and should be able to have kids when they so choose.
That said, the pregnancies I immediately thought of that you guys didn't already touch on were How I Met Your Mother and Bones. I forget what season it was that both Alyson Hannigan and Cobie Smulders were pregnant, but I've never seen so many enormous handbags in one place. And Bones definitely accelerated Bones and Booth finally getting together (skipping some of the fun stuff, some might argue) by writing in Emily Deschanel's pregnancy.