In the case of switching the eggs, is it possible that the host mother would be more likely to reject it? Because in that case, I feel it's a fairly clear case in which you have directly affected one's ability to have a family by doing this.
Not sure about one woman's eggs in another woman, but this is certainly true of an anonymous sperm donor. In order to have the lowest chance of pre-eclampsia the woman needs to have been exposed vaginally to the man's semen for six months. Donor sperm children thus have higher rates of pre-eclampsia in pregnancy.
