I have just started taking the combined birth control pill Rigevidon and I have heard that it stops ovulation. If I am taking the pills perfectly at the exact same time every day for three weeks with one week break between each pack, then how come it is only over 99% effective and not 100% effective? Since it stops ovulation and you can't get pregnant if there is no egg, where does the <1% ineffectiveness come from? Also, does that mean that I would ovulate during the one week I am not on the pill each month?