Say, so, is Baltar infertile?

I mean, hang on here, we know that cylons are all about the babymaking, and yet Six and Three both slept with him maaaaaaaany many times without getting pregnant. I mean, maybe cylon disco baseships have condom machines, but I'm kind of betting not.

Possibly everyone else already has theories that account for this and I am just really slow, which is understandable given that all of my theorizing energy goes toward SGA and figuring out when and where Rodney and John have been doing it.