I´m so sorry about the confusion I´d created and the double negative. I think i´m going to fail my next English test    As you can see, English is not my first language. It is Spanish which is much easier than yours.
So, what i wanted to say is that my pregnant sim didn´t eat a cheesecake during her pregnancy. I hope that is gramatically correct 

I don´t think the cheesecake has nothing to do in my case. Anyway, next time i´ll play i will try to remove the CC and triy a new pregnant and let´s see what happen. i will let you know. Thanks all of you.

It went over all the pregnancies i had in my neighbourhood. About eight pregnancies, more or less

No, the sims have nothing in common. And the number of children that the sims give birth are two. I didn´t know that one sim could have more than two babies at the same time.
I save the game in the moment right before the birth. When the twins are born i abandoned the game without saving and i tried (i did it a lot of times) again for a different birth, but it comes again two children. 

I have all expansions pack, but the new free time one.

I don´t know if this post is in the right place. I´m so sorry if not.
My problem is that every time a sim is pregnant, she always give birth to two new baby sims. I didn´t type 'force twins' comand. And i also uninstalled any hack that would produced that thing in my game. As i didn´t get any results, i tried uninstall and reinstall tha base game and the expansions again. But the problem is still here. I removed all the custom content only to make a prove. I´m at that point that i don´t know what to do next.   Any ideas about what is happenning in my game? Any help? What more can i do? Please, help me.
Thanks in advanced