Studies on zero-G pregnancy?

I was writing about 2001: A Space Odyssey, which got me thinking about space colonization. Naturally, for them to be sustainable, humans would need to be able to reproduce. I remember NASA was running some studies about sexual attraction under zero-G conditions, but I was wondering whether they've actually looked at the feasibility of gestation and birth without gravity. Has anyone heard of any studies done (probably with animals) on this subject, by NASA or any other agency?