Girlology: A Girl's Guide to Stuff that Matters

Your monthly cycle begins on the day you start your period. Hormones from the brain tell the ovary to start getting an egg ready. In the ovary, the egg grows in a little sac of fluid called a follicle. The follicle makes estrogen that causes the endometrium to grow a thick and lush lining. When the egg ovulates (which means it pops out of the ovary), the follicle then makes progesterone that prepares the endometrium for a pregnancy. If the egg is not fertilized by a sperm from a male, a pregnancy does not occur. With no pregnancy, the ovary stops making the progesterone, and that signals the endometrium to shed the lining (and that’s a period). As the period begins, the brain signals the ovary to start over with a new follicle and a new lining in the endometrium. This amazing cycle then starts all over again!

Want the short report? Egg matures > egg ovulates > egg travels down fallopian tube and into the uterus. No pregnancy? Then the uterus recognizes that and sheds the old lining, which starts a period. Now that’s an easier story to follow!

Another way to say it: It’s kind of like a bed is made in the uterus for a baby to grow in. If there’s no baby there, the uterus decides it’s time to change the “bed,” sort of like changing the sheets. How often do you change your sheets? In your uterus, it’s once a month!

And even if you don’t want it, here’s the long report.

Cycle day 1. The first day you have menstrual bleeding is always considered day 1. It’s usually anywhere from 25 to 35 days after your last period. Everyone always seems to think that period cycles are always 28 days or one month . . . but everyone is a little different, and cycles can be longer or shorter (anywhere from 21 to 45 days) and still be normal.

Cycle days 1–7. Periods usually last anywhere from three to seven days, but you only lose about two tablespoons of actual blood in all that time. It seems like more doesn’t it? That’s because of the other fluids and tissue that are released (think of them as the pillow cases and bedspread that need to be cleaned, too). Your bleeding is happening because there is no pregnancy, and the uterus has decided to release the old lining and begin a new lining (change the sheets!).

Your uterus pushes out the period (old sheets) by contracting its muscular walls. Some girls will feel these contractions as cramps.

Cycle days 7–12. At the same time that you are having your period, your brain and ovaries are already talking. Your brain is recruiting another egg for the next cycle, and your uterus is getting orders to prepare a fresh lining. Your hormones are helping with all this communication. The follicle (which holds the recruited egg) in your ovary is making that hormone called estrogen that helps thicken the lining of the uterus. So as soon as your bleeding is done, your uterus is already “fluffing up the sheets,” or getting a new lining ready for the next cycle in case an embryo is on the way. Now for this whole thing about babies. Your body needs a lot of practice with its cycles before it’s really ready for a baby. That’s why you start your periods way before you are ready to actually have sex and get pregnant.

Cycle days 12–14. Ovulation time. Now that the next egg has been recruited, it is ready for take off. The follicle that it has been growing in will open up and let it go! This is called ovulation. Some girls actually feel a slight twinge or cramp when this happens. If there is discomfort, it’s called mittelschmerz (dare you to use that in your next English paper!!). That’s a German word that means “middle pain.” Most girls are clueless that such an amazing thing is happening in there.This is the time when you may also notice that your vaginal discharge seems a little more watery or slimey. This happens because your hormones tell your cervix to change the discharge to make it easier for sperm to pass through. The cervix says okay, and makes the discharge extra slippery. Pregnancy can happen during about eight days every cycle. The six or seven days before and two or three days after ovulation are the days that pregnancy is most likely to happen if you are having sex. Because ovulation is unpredictable and young girls’ cycles are not always the same every month, it is really hard to figure out exactly when pregnancy can or can’t happen.