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    Getting your period is a rite of passage surrounded by whispered rumor and mystery. Some girls dread it. Others can't wait. But all girls menstruate, and it helps to understand what's going on. Here are answers to seven common questions about a girl's period.

    Why Do You Have a Period?

    During the month, blood builds up in the lining of your uterus, which will help a baby develop when you're older and want to have a family. It's a natural process, says Sharon Horesh Bergquist, MD, at the Emory School of Medicine in Atlanta.

    Most of the time, a fertilized egg is not implanted in your uterus, and the blood sheds out of your body during your monthly period.

    What's Really Going On?

    All kinds of changes occur in your body during your menstrual cycle. “The thing that makes it all happen is hormones,” says Atlanta pediatrician Deborah Pollack, MD. “You get hormone surges at night, with higher and higher and higher peaks, until your period begins.”

    Raised levels of hormones helps eggs grow in your ovaries. Each month, one egg is released into your Fallopian tubes. This is called ovulation. The egg travels down the tube to your womb. And while this happens, your uterine lining thickens with blood -- just in case an egg is fertilized by sperm.

    If the timing is right, the egg and sperm join together, and the fertilized egg attaches to the lining of your uterus. Pregnancy begins. Without a fertilized egg, the thickened lining has no purpose. So it sheds and comes out through your vagina. Your period has arrived.

    When Will You Get Your Period?

    The average age to start your period is 12, but many girls start younger, and others start later. "When you first start to get breasts and some pubic hair, you can usually jump forward two years and guess that’s when you’ll start, says Pollack.

    “It might take up to two years for your period to get regular because the hormone surges are uneven,” Pollack says. At first, it's common to have one period, and then not another for a few months. But even if you don't have a period every month, you can still get pregnant.

    Many girls start their periods around the same age as their mothers did. So ask your mother when she started her period, and how it felt. If you haven't started your period by age 16, you should talk to your doctor.

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