Taking medication while being pregnant is very dangerous. Some medicines like topical retinoids and Tetracycline tablets may damage the fetus bones and teeth. It is clear that this kind of treatments should be stopped during pregnancy. But even  less harmful medicines are not appropriate while being pregnant. Then we are talking about creams containing the well known anti-acne substance benzoyl peroxide. It makes the skin dry out but because a pregnant woman automatically develops a dry skin and therefore treatments based on benzoyl peroxide are not appropriate. Of course this does not mean that there are no acne skin care products for pregnant women. Some milder solutions and natural treatments can have very positive effects.