The progestin in the Minipill may prevent ovulation; however it may not do this reliably each month. The Minipill works further by thickening the mucous around the cervix and preventing sperm from entering the uterus. The lining of the uterus is also affected in a way that prevents fertilized eggs from implanting into the wall of the uterus. The Minipill is taken every day. You may not have a period while taking the Minipill, if you do have periods that means you are still ovulating and your risk for pregnancy occuring is greater.
Combination birth control pills come in either 21 or 28-day packs. You take one pill each day at the same time for 21 days. If you have a 21-day pack, you stop taking birth control pills for 7 days at the end of the pack. If you are taking a 28-day pack, you continue taking pills every day, the last 7 non-hormonal pills serve as a reminder to help you remember to take your pill at the same time every day. Your period will occur during the week you take the 7 reminder pills.