I quit aikido upon learning I was pregnant; the rolling around just didn't seem "right" to me (I was nikkyu at that time too)and I was worried about injuring my baby. My ukemi was not as good as it should have been. I know of a woman who has trained sucessfully through two pregnancies, until her 8th month (and I think even into her 9th, just doing weapons practice). Your wife will be able to tell what is right for her, as the body has a way of telling you whether something is right or not. I did start training again 4 months after my son was born.