Did you know that just changing the orientation of chicken and frog eggs while they're gestating can mess things up? Never mind actually changing the magnitude of the g vector.
The lack of basic research in this area is not good. The moon has around 1/3 g. Mars around 2/3g. Can baseline humans and other large mammals reproduce successfully at that acceleration? I'm just an internet know-nothing know-it-all, but I give 70% against lunar G being sufficient and 60% against Martian.
We don't have good ways to study this on earth. We've done fun stuff like fly human jizz on a vomet-comet and roll plants, cells, tissue samples and small animals around in Clinostats and Random Positioning Machines (big, slow-moving rotating drums and gimbaled doohickies). But apparently all we really know is that larger mammals don't have the specific vulnerabilities that birds and frogs do: having a yolk seems to make them more sensitive to the direction of G, because of chemical diffusion:
Gravity sensing in individual cells in mammals has also not yet been defined. Unlike frog, where free-living embryos arise from oocytes with maternally differentially-deposited nutritional heavy yolk, mammalian embryos rely on maternal nutrition after implantation and have little yolk. Thus, mouse embryos are not thought to sense gravity by macromolecular (yolk) distribution sensed by the cytoskeleton, as reported in frog..
AFAICT, there's no large centrifuge on the ISS -- JAXA built a module intended to house a decently sized centrifuge (specimens up to 24" tall), but the plans to launch it were cancelled. AFAIK, there's certainly nothing on the drawing board that would be big enough to actually accommodate human experiments. This seems like one of the highest value things NASA could do with ISS.
My guess is that if 0.38g ain't enough this will probably need some next-level genetic engineering to be worked around.