I have to say it's pretty unnerving to have a steady stream of invisible babies.

Hmm... that's definitely an idea to try.  I've been using fixall consistently throughout the game since I end up with bad sims and crossed wires frequently, but I haven't done it before/during labor.  Next go-round I'll give it a shot.

First things first: I'm still on WA, with a legit copy of both base game and expansion, using AwesomeMod plus some slider hacks.  I searched through the forum but didn't find this particular bug, but then I am kind of crap at finding things, so apologies if it's been covered somewhere.

My sim got pregnant, and when it came time to give birth, she hopped off to the hospital with hubby and commenced popping out babies.  A LOT of babies.  I got the text dialogue to name the child (a girl) and give her traits, and then a please-name-the-baby box popped up yet again.  Thinking this was possibly twins (I haven't had a birth in the game before, so I'm not sure if you get separate notifications for twins or if they're both announced right off the bat) I named this one and gave her traits.  A third box popped up, which was when I thought something might be wrong... and I went through seven babies popped before going into the command prompt for a 'fixall'.  The babies stopped, but none of them never appeared.  My sim didn't have a pregnant moodlet anymore, but she still had the pregnancy mesh and could still do pregnancy-related actions.  Both the mother and the father seemed to think the babies existed, because they had wishes to hold them, but so far as I could see they weren't anywhere to be found.

I thought it might have been a one-off bug, so I restarted the game and played through it again without letting her go to the hospital (just in case they got stuck in the rabbit hole).  No dice; the same thing happened except this time they were all boys instead of all girls.  By the seventh baby I went for a fixall, and the mother stopped giving birth, but there were no babies and she was still visibly pregnant.

So... I am at a loss.  The next step, I suppose, is to drag out all the CC and try again, but I'm betting it's not AwesomeMod doing this and I am dubious as to whether the slider hacks would have anything to do with it... so if anyone has any advice/wisdom/similar experiences/fixes, I'm all ears.  (And I just might worship you a little.)