[FIXED] NPCs Sims almost always having twins
Preface: I play with the base game and GTW expansion. No mods.
I have two separate households where I'm actively planning children. One household, a wife/husband, has had one set of twins (boy/girl). I had read that was really rare, so I thought that was pretty cool. This happened about one week ago (real time). I have not tried for children with them again.
My second household is a single male. I'm doing a bit of a challenge in trying to see how many townies he can have a baby with. So far, he's had a baby with 4 different women. One woman was in play (first mother), the other three were unhoused townies out of play that I added to a Lot before they gave birth. Every single one of these women have had twins: boy/girl, boy/girl, boy/girl, girl/girl. The fourth woman, before she gave birth, I played her while she was in labor (I wanted to send her to the hospital and see how that played out, but couldn't figure out how). I was surprised (and pleased) to see she gave birth to a single daughter. Being a programmer by trade, I was curious if the singular child made any difference in me playing her. So I reverted to a save just before she gave birth, played my male Sim and he got a call shortly thereafter - TWINS: girl/girl. So I loaded the save again, played the mother a second time and she gave birth at home where she had only one child: daughter. Reverted a third time to the save, played the man and got the call for twins: girl/girl.
Breakdown:
Mother 1: boy/girl twins
Mother 2: boy/girl twins
Mother 3: boy/girl twins
Mother 4: girl single; girl/girl twins; girl single; girl/girl twins
I did some research and it looks like back in December an overabundance of twins was reported as a bug and reported as resolved. I will say that my male Sim did "Try for Baby" with all of the women at least twice, with the exception of the fourth woman. The first mother didn't get pregnant the first try, so from that point forward I've always tried for a baby twice in a row, one right after another. With the fourth woman he didn't get a chance to try a second time as she left before there was an opportunity to (a guy has got to eat). The married Sims that also had the twins tried for a baby only once, so trying multiple times may not matter.
It's also important to note that none of my Sims have the fertility buff. The only similarity between the married couple and my single male is that all three are "romantic", otherwise they are completely different.
Edit: Clarified some information.
I had this very reproducible in one of my earlier saves but not in the current one.
One pair of twins, 6 single babies.
I'm marking this as fixed but feel free to come back