I suppose another way of looking at the question is: how important is gravity for the development of mammal fetuses?
And if things would go wrong, what sort of things would they be, and what would be the result?
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There is some evidence that fetal development under zero gravity conditions might be problematic.
Wakayama S, Kawahara Y, Li C, Yamagata K, Yuge L, et al. (2009) Detrimental Effects of Microgravity on Mouse Preimplantation Development In Vitro. PLoS ONE 4(8): e6753. doi:10.1371/journal.pone.0006753
The paper is here.
These authors studied aspects of reproduction of mice in a clinostat under 10-3G. They found that fertilisation was unaffected, but that preimplantation development of the embryo was affected by the mG environment.
The introduction to the paper gives a good brief review of this area of research. Perhaps of particular relevance is this section:
In the STS-80 space shuttle mission, mouse 2-cell embryos were collected on the ground, launched into space and cultured for four days in µG. The control embryos on Earth developed to normal blastocysts, but in the space flight group, none of the embryos showed any sign of development, and all degenerated (Schenker & Forkheim, 1998) . A more reliable experiment was done on the Cosmos 1129 mission in 1979, when mature male and female rats were sent into orbit and then allowed to intermingle in a common breeding chamber (Serova & Denisova, 1982). However, none of the females gave birth, although postflight examinations revealed that ovulation had occurred. Two of the females were reported to have achieved pregnancy, but the embryos appear to have been resorbed.
Schenker E, Forkheim K (1998) Mammalian mice embryo early development in weightlessness environment on STS 80 space flight. Israel Aerospace Medicine Institute Report.
Serova LV, Denisova LA (1982) The effect of weightlessness on the reproductive function of mammals. Physiologist 25: S9–12.