context: Think you know all there is to know about your period? Women have about 450 periods during their lifetime, which means you have plenty of chances to learn all about it. Even so, your period can still manage to surprise you -- and not just by showing up when you least expect it. Did you know these five facts about your monthly visitor? It's time to squash that age-old myth: Your period doesn't protect you from pregnancy. There are a couple of reasons why. First, some women may bleed when their ovaries release an egg each month, called ovulation, and mistake it for their period. You're at your peak fertility when you ovulate. So if you have sex during this time, it could actually make you more likely to get pregnant. Second, you may ovulate before your period is over or within a few days after the bleeding stops. Since sperm can hang out in your body for up to 3 days, having sex during your period could lead to conception. Use a condom or other form of birth control to prevent an unplanned pregnancy, no matter what time of the month it is. Sure, you bleed during the week that you take the sugar pills. But technically that's âmonthly withdrawal bleeding.â It's slightly different than a regular period. Normally, you ovulate in the middle of your menstrual cycle. If the egg your ovaries release isn't fertilized, your hormone levels drop, causing you to shed the lining inside your uterus, and you get your period. Birth control pills, though, prevent ovulation. With most types, you take hormones for 3 weeks followed by 1 week of pills without them. Though they keep your body from releasing an egg, they don't prevent it from building up the lining of your uterus all month. The period-like bleeding during that fourth week is your body's reaction to the lack of hormones from the last week of the pill. Just when you start to feel like you can predict exactly when your period is going to show, everything can change. For that, you can thank the hormone shifts that happen throughout your lifetime. Once you get your very first period, your cycles may be longer, meaning more time may pass between when one period starts to the next. A typical cycle for a teenage girl may be 21 to 45 days. Over time, they get shorter and more predictable, averaging about 21 to 35 days. Hormone changes that happen during perimenopause -- the years before menopause when your body starts to make less estrogen -- can throw you for a loop. The time from one period to the next may get shorter or longer, and you may have heavier or lighter bleeding during your period. This phase can last up to 10 years before you start menopause and stop getting your period for good. Gradual life changes are normal, but sudden, unusual issues like very heavy bleeding or missed periods are not. Talk with your doctor if you notice that something seems off. You have more options to help you manage that time of the month. A menstrual cup is a flexible cup that fits inside your vagina and collects blood during your period. Period panties are super-absorbent, and you can wear them on their own on your lighter days or with a tampon during heavier times. Reusable cloth pads can be washed and worn again. These products can be cost-savers, since you can reuse them, and they also create less waste. In some cases, they give you more time between changes. For example, you need to change a tampon every 4 to 8 hours, but you may be able to go up to 12 hours with a menstrual cup before you empty it. There are pros and cons to all these options, just as there are with tampons and pads. But you can find one that works best for you with some trial and error. It's 1 or 2 weeks before your period starts, and here come the breakouts, sluggishness, cravings, bloating, and mood swings. Sound familiar? Every woman is different, but for many, PMS is a fact of life. But doctors don't know exactly why that is. It seems to be a mix of hormone changes during your menstrual cycle, chemical changes in the brain, and other emotional issues you might have, such as depression, that can make PMS worse. What's more, once you get your period, the rollercoaster may continue. One study found that period-related pains such as cramps, bloating, backaches, and headaches can cloud your thinking, because the pain may make it harder for you to focus on the tasks at hand. Not that you can't still do them -- you can. It may just feel like it takes more work. Lifestyle changes are usually the best way to take control of PMS. Aim to get about 30 minutes of exercise most days of the week, get 8 hours of shut-eye per night, and don't smoke. Your diet makes a difference, too, so fill up on fruits, veggies, and whole grains while you limit salt (hello, bloating) as well as sugar, caffeine, and alcohol. Let your doctor know if PMS keeps you from doing what you normally do, or if you have symptoms of depression or anxiety. You may have a more serious condition called premenstrual dysphoric disorder ( PMDD) that needs medical attention.