Center for Young Women's Health

Menstrual Periods



  • Periods usually start between 9-15 years of age.
  • Periods may be irregular the first year.
  • It's a good idea to keep track of your periods.

Why do I get a period?

You are born with two small, grape-shaped ovaries inside of your belly on either side of your uterus. Ovaries are filled with hundreds of thousands of eggs. When you reach puberty and you are becoming a woman, your ovaries make hormones (especially estrogen) that cause breast development and menstrual periods. The pituitary gland in your brain releases chemical messengers (FSH and LH) called gonadotropins, that "tell" the ovaries to release a mature egg once a month. The egg then travels towards the uterus. If the egg isn't fertilized by a sperm, then two weeks later, the thick, bloody lining (called the endometrium) that builds up in your uterus between periods, passes out of your body through your vagina. This flow, which comes out as blood, is your menstrual period. The whole process is called menstruation, and it will begin when your body is ready.


Female Reproductive Anatomy


What will my period feel like?

Your period feels like liquid flowing slowly, with starts and stops, out of your vagina. This is exactly what happens during your period. Although it may seem like a lot of blood, only a small amount is released at a time. It's normal to see small clots of blood from your vagina on the toilet paper after you pass urine.


What if I haven't had my period yet?

It's normal to get your period as early as 9 years old or as late as 15 years old. This is a big time range and it's hard to be one of the first or one of the last. Girls who are active in sports or are very thin may not get their period until a later age. Losing weight while you are in your growth spurt can also delay your periods. Talk to your parent or your health care provider (HCP) about your worries and concerns. If you haven't gotten your period by the time you are 15 OR if you started your breast development more than three years ago and haven't gotten your period, get a check-up with your healthcare provider just to make sure everything is okay. Your HCP sees many girls who develop late, so don't be embarrassed to ask. Your HCP may do a genital exam and check to see if your hymen (a thin piece of tissue that partially blocks the entrance to the vagina) is open. Some girls are born with an "imperforate hymen," which means that the hymen doesn't have an opening, and blood cannot leave the vagina. Some girls are also born without a vagina and/or uterus (MRKH), so they don't get their period for this reason. Other girls may have a hormone imbalance, low weight, or stress. It's a good idea to get regular check-ups during puberty just to make sure that everything is okay.


How often should I get my period?

You should get your period once every month. Your menstrual cycle should be about 28 days. This means that there should be about 28 days from the first day of your period to the first day of your next period. 28 days is an average number, but anywhere between 21 and 35 days is normal. Your period will usually last between 3 and 7 days. The amount of blood flow you have will probably be different each day. You will usually have the most blood in the beginning of your period and the least towards the end. When you are first getting your period, you may have a very heavy period one cycle and very light one the next.


What if my periods don't come regularly?

You may be one of those young women whose periods may be affected by changes in body weight or diet, increased stress, eating disorders, exercise, illness, or going away to college. Remember that if you are having sexual intercourse, an irregular period could be a sign of pregnancy. Your period may last 1 day or it may last 7 or 8. All of your cycles may not be the same number of days, and the length of your cycle may change over time. It is common for a girl just starting her period to have irregular periods for a year or two.


Periods too far apart. You may only get your period 3-4 times a year, instead of once a month. If you are having your periods only a few times a year, this may be because of stress, intense exercise, weight loss, or diet. Too few periods could also be caused by a mild hormone imbalance called Polycystic Ovary Syndrome (PCOS). PCOS is especially likely to cause irregular periods if you also have acne, excess hair growth, or weight problems. You should talk with your HCP if there are more than 35 days between your periods.


Periods too close together. You may get your period every two or three weeks. This can be because of stress, some types of exercise, or other changes in your life. If your periods are less than 21 days apart, or if your period seems to be too heavy, your provider may want to check your blood count to see if you are anemic. If you're anemic, you have too few red blood cells and too little hemoglobin (oxygen-carrying protein in your red blood cells). People who are anemic from heavy periods need to eat foods that are a good source of iron and take an iron supplement.


Why should I track of my period?

Keeping track of when your period starts and stops is a good way to see if there is a pattern to your menstrual cycle. It is also important to write down how many days you have your period and the amount of flow you have. Bring your Period Trackers with you when you see your health care provider so that he or she can evaluate your cycle.


My Monthly Period & Symptom Tracker

My Monthly Period & Symptom Tracker is an easy way to keep track of your menstrual flow, and it’s also a way to keep track of cramps, and/or PMS and period symptoms (if you have them) each month.

Sample Monthly Period & Symptom Tracker


My Monthly Period & Symptom Tracker


My Yearly Period Tracker

My Yearly Period Tracker is a simple and convenient way to track your period throughout the year.

Sample Yearly Period Tracker


My Yearly Period Tracker


What if I skip a period?

If you miss your period, it could be because of a change in your body or in your life. If you are under stress, you've been sick, or you've lost weight, you may skip a period. It is common to skip a period once in a while, especially during the first year that you are getting it. However, if you are having unprotected sexual intercourse or close sexual contact, or if your birth control method has failed, it could also be that you are pregnant. If you think you may be pregnant, it's very important to have a pregnancy test. If you're not pregnany and skip several periods, you should talk to your HCP and see why this is happening.


What if I have big clots of blood during my period?

Dark, chunky clots of blood can be perfectly normal. Many women get them during their period when they have days of heavy cramping and heavy bleeding. Your body usually makes things called "anti-coagulants," that keep your blood from clotting as it moves to the vagina and out of your body. However, during days of heavy bleeding and cramping, your body is pushing blood so quickly out of you that your body does not have time to release these anti-coagulants. Your blood then clots. If you have clots that are bigger than a quarter, it's a good idea to talk with your HCP.


What if I get spots of blood on my underwear between my periods?

Bleeding in the middle of your cycle could mean different things. Some women bleed a little bit during the middle of their cycle, when they ovulate (when a mature egg is released from the ovaries). This is nothing to worry about. Other times, "spotting" occurs because of an infection such as a sexually transmitted infection (if you are having sexual intercourse). Very rarely, "spotting" can be because of a polyp (a benign tumor that may need to be removed surgically), but this is not very common. You should talk to your HCP if you have bleeding when you don't have your period.


Written and reviewed by the CYWH Staff at Boston Children's Hospital


Updated: 3/5/2014


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