I do not believe there is any risk to the pregnancy from either microdermabrasion or glycolic acid peels although I understand my colleagues cautionary reserve.  My bigger concern is that the melanocytes in the skin are turned on in pregnancy (causing melasma - the so called mask of pregnancy) and therefore the risk of post inflammatory hyperpigmentation after the peel is a significant.  If that occurs, you would be unable to use the standard bleaching agents to remedy the problem until after the pregnancy.