Birth control pills can either be monophasic, where you get the same amount of hormones each day, or triphasic, where you get a different amount of hormones over 3 weeks.
When you take a monophasic birth control pill, each 4 week supply contains 3 weeks of hormones and one week of sugar pills. So if you want, you can get your period every month by using as directed, or you can skip the week of sugar pills and start on the second pack of hormone pills. Seasonale makes things eaiser by skipping the sugar pills all together thus keeping Aunt Flo at bay for 3 months at a time.
When you're on any birth control pill, when you get your period, it isn't a real period because you're not actually releasing an egg (the pill stops you from ovulating). It's called a "pill period," and is a result of your body's reaction to withdrawing from the hormones. Having this kind of period once a month is just as safe as only having it 4 times a year, hence taking a pill like Seasonale.
Dear's Tip: Monophasic birth control might be right for you if you suffer from painful periods, excessive bleeding, bad PMS symptoms, or unbearable mood swings, but definitely consult your doctor before altering your prescriptions.