Its hard to say exactly because everyone and every pregnancy are different but its most likey to begin and be at its worst the first trimester. This is due to the inbalance and increase of progesterone. Your skin is going through an overproduction of oil. This in turn clogs your pores and creates bacteria to build up. If lucky, it will decrease or go away after the first trimester due to the estrogen increase. People with acne already will either get worse OR will clear up when pregnant, and then on the other hand, people who never have acne are very likely to get it! Here are some tips to help reduce acne: 1. DRINK TONS OF WATER....8 glasses a day, up to half gallon 2. Take your prenatal vitamins daily, VERY important for you and the BABY 3. Wash your face twice a day only. Use oil and so