Do you ovulate on the birth control pill?
Unlike other birth control methods (such as copper IUDs), the pill works by suppressing ovulation. In a regular menstrual cycle, a series of hormonal fluctuations causes ovulation. The pill induces a steady state of hormones so that ovulation does not occur.
It takes about a week for the pill to induce this steady state. Therefore, it really doesn’t matter where you are in your menstrual cycle when you start. As long as you use condoms (or abstain from sex) for seven days after starting the pill, you’ll be protected from pregnancy. Just be sure that prior to starting the pill, you haven’t had unprotected sex since your last period.
After a few days without the pill, hormones start fluctuating again and ovulation can occur. If you miss one pill, it’s ok to take two pills the following day–ovulation is not likely to happen that quickly. But if you miss two or more days of pills, it will take a week for the pill to get your hormones back into a steady state.
Any unprotected sex after skipping two or more pills can cause pregnancy, so it’s important not only to resume the pill, but also to take emergency contraception within five days of unprotected sex.