Twins so rarely happen in my game anymore that I haven't thought much about them in what seems like forever. I do have a slight preference for two girls since I create and play female sims almost exclusively, but I never do anything to influence outcomes of pregnancies. I let my sims have whatever chance gives them. I love the anticipation, what will it be, girl or boy? How many? When they get to the third trimester I'm like, hurry up, hurry up, I have to know which it's going to be, now.