Key Facts About the Menstrual Cycle

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Key Facts About the
Menstrual Cycle
What is menstruation?

The INFO Project
Menstruation is the shedding of tissue and blood from the lining of the womb through a
woman’s vagina. This process takes place about once a month during a woman’s reproductive
Johns Hopkins Bloomberg
School of Public Health
years. Menstruation is also called monthly bleeding, menses, menstrual course, menstrual period,
Center for Communication
and period.1
111 Market Place,
Why does a woman have
Suite 310
Baltimore, Maryland 21202,
monthly bleeding?
Monthly bleeding happens when a woman
has not become pregnant in the few weeks
before her bleeding starts. The lining of
the womb builds up in these weeks in case
pregnancy occurs. When pregnancy does
not happen, this tissue and blood is shed.
How long does monthly
bleeding last?
Usually, from two to seven days, often
around fi ve days.
Is the bleeding dangerous to a
woman’s health?
Not usually. A woman’s monthly bleeding
is not like bleeding that occurs with a cut or wound. Most of the menstrual fl uid is extra tissue from
the lining of the womb. It contains only about 10 ml to 35 ml of blood over the course of a menstru-
al period. If a woman has heavy bleeding every month, however, it could contribute to anemia.
Why does the bleeding happen again and again?
A woman’s body goes through a cycle, or process, of getting ready for pregnancy each month. This
is called the menstrual cycle. She can get pregnant only on certain days of that cycle. If she does
not get pregnant, then she has monthly bleeding, and the process starts over again. If she does get
pregnant, though, monthly bleeding stops.
Just what happens in the body during the menstrual cycle?
Hormones in a woman’s body start a few eggs growing, and one is released into one of the tubes
that are attached to her womb (see chart, p. 3). The egg travels down the tube on its way to the
womb. This takes several days. During this time the lining of the womb is thickening, getting ready
in case an egg is fertilized by a sperm that has traveled up from the vagina after vaginal inter-
course. If a sperm reaches the tube at the right time and joins with the egg, and then this fertilized
egg attaches itself to the lining of the womb, the woman becomes pregnant. But if the egg is not
fertilized by sperm, the egg breaks up, and the womb sheds its thickened lining because it will
not be needed that month. The lining passes out of the body through the vagina.
When can a woman get pregnant?
If a couple is not using family planning, vaginal intercourse can lead to pregnancy

when it takes place in the fi ve days before a woman’s egg is released or on the
day that the egg is released. If sex takes place during this time, the egg and
sperm can reach the tube at the same time, and an egg may be fertilized.

1 These terms for menstruation are used interchangeably in this report.
August 2006 • Issue No. 7
“W Change



A woman’s egg is released once a
How To Use This Tool
month, usually about midway between
two menstrual periods. The exact timing
This tool offers health care providers, educators, and
is diffi cult to predict, however. Women
communicators a quick reference to answer common
with 28-day cycles (see next question)
questions about menstruation and the menstrual cycle
that girls, women, male family members, and other com-
are most likely to be fertile between
munity members have. It also answers questions about
days 8 and 15 of each cycle.
how some contraceptive methods affect the menstrual
cycle. Information is presented in a simple way and ac-
How are the days of the
companied by illustrations that can be used with clients.
menstrual cycle counted?
It is a companion tool to the “When Contraceptives
Change Monthly Bleeding” Population Reports issue.
A menstrual cycle starts with the fi rst
day of monthly bleeding. The last day
of the menstrual cycle is the day before
the next monthly bleeding starts. For example, if bleeding started on July 1, that is the fi rst day of
the menstrual cycle. If the menstrual cycle that month is 28 days long, the next monthly bleeding
would start on July 29.
If this woman usually
has 28-day cycles, she
This report was prepared by Ruwaida M. Salem,
can expect monthly
MPH and Vidya Setty, MPH.
Research assistance by Faraz Naqvi, MHS
bleeding to start again
and R. Taylor Williamson, MPH.
on August 26.
Ward Rinehart, Editor.
Richard Blackburn, Editorial Supervisor.
Francine Mueller, Designer.
How long does the
INFO Reports appreciates the assistance of
menstrual cycle
the following reviewers: Dinesh Agarwal, Jean
usually last?
Ahlborg, Ravi Anand, Bruno M. Benavides,
Jane T. Bertrand, Gloria Coe, Soledad Díaz,
Most women have men-
Anna Glasier, John Guillebaud, Ellen Hardy,
Robert A. Hatcher, Monica Jasis, Jan Kumar,
strual cycles that last
Enriquito R. Lu, Shawn Malarcher, Diana
between 24 and 35 days.
Mansour, Leslie Miller, Anita L. Nelson, Tonya
Nyagiro, Malcolm Potts, Pauline Russell-Brown,
The most common length is 28 days. But many women
Stephen Settimi, Marni Sommer, J. Joseph
have longer or shorter cycles. The length of some
Speidel, Martin T. Vaessen, Marcel Vekemans,
and Mary Beth Weinberger.
women’s cycles varies by a few days from month to
month. All these patterns are normal.
Suggested citation: Salem, R. and Setty, V.
“Key Facts About the Menstrual Cycle.” INFO
Reports. No. 7. Baltimore, Johns Hopkins
Why would a woman want to keep track
Bloomberg School of Public Health,
of the length of her menstrual cycles?
The INFO Project, Aug. 2006.
Keeping track of the menstrual cycle helps a woman
Available online:
know when to expect her next monthly bleeding. If her
menstrual pattern suddenly changes, it could be a sign of
The INFO Project
a health problem, and she can seek help. Also, keeping
Center for Communication Programs
The Johns Hopkins Bloomberg
track of the days in a cycle is necessary to use the Stan-
School of Public Health
dard Days Method®, a fertility awareness-based method
of family planning. If a woman wants to get pregnant,
Earle Lawrence, Project Director;
Stephen Goldstein, Chief, Publications Division;
keeping track of her menstrual cycle can help her identify
Theresa Norton, Associate Editor;
the days when she is most likely to get pregnant.
Linda Sadler, Production Manager.

INFO Reports is designed to provide an
The Menstrual Cycle at accurate and authoritative report on important
developments in family planning and related
health issues. The opinions expressed herein are
Different Times of Life those of the authors and do not necessarily refl ect
the views of the U.S. Agency for International
Development or the Johns Hopkins University.
When do girls usually start having
menstrual periods?
Girls usually start to have periods between the ages
of 11 and 16, and on average between 12 and 13.
U.S. Agency for
As socioeconomic conditions and nutrition have
International Development
improved, the age at which a girl’s period starts has

Published with support from USAID, Global, GH/POP/PEC,
gradually decreased. In some parts of the world, it is not
under the terms of Grant No. GPH-A-00-02-00003-00.
uncommon for girls to start their periods before age 11.



How does a girl know when she will begin to have periods?
A girl cannot know for sure when she will begin to have periods. However, a girl’s fi rst period usually
comes about a year after her breasts begin to develop and after her pubic hair becomes coarser
and darker.
Do adolescent girls have different cycle lengths than adult women?
The lengths of adolescents’ cycles vary more than for adult women, especially in the fi rst two to three
years. Cycles become more regular with time. Most adolescents’ cycles range between 21 and 45 days.
For women in general, 24 to 35 days in length is usual. Menstrual bleeding for adolescents usually lasts
between two and seven days, the same as for adult women.
Why do women stop having menstrual periods during pregnancy?
When a fertilized egg attaches to the lining of the womb and starts to develop into an embryo, it signals
the body to release certain hormones. These hormones help keep the lining thick and prevent it from being
shed as menstrual bleeding. The thickened lining helps protect and nourish the embryo. Later the lining
becomes part of the placenta, which protects and nourishes the fetus until birth. These same hormones
also stop the ovaries from releasing additional eggs.
Is bleeding just after giving birth the same as menstrual bleeding?
No, this kind of bleeding is not menstrual bleeding because it does not follow the release of an egg.
After childbirth, the womb contracts in order to expel the extra blood, tissue, and mucus left over from
the pregnancy, and to return to normal size. This bleeding gradually decreases during the weeks
following childbirth.


If a woman is not breastfeeding, how soon after
childbirth can she get pregnant?
For women who are not breastfeeding, menstrual cycles can start again
as soon as three weeks after childbirth. Some women may be able to get
pregnant again even before monthly bleeding resumes.
What keeps monthly bleeding from starting again for
some breastfeeding women?
Just after childbirth a woman’s body releases a hormone that signals
her breasts to produce milk for the baby. This hormone also blocks
other hormones that would lead to release of an egg from the ovary. If a
woman breastfeeds her baby, the baby’s active suckling keeps the level
of this hormone high, and so she does not release eggs. When the baby’s
suckling eventually becomes less frequent, her menstrual cycles—and
thus her ability to become pregnant—soon return. The time it takes for
monthly bleeding to resume cannot be predicted and differs for each
woman. It can depend on how frequently and intensely she breastfeeds,
her age, how many children she has, and on biological differences among
individual women.
When do women usually stop having menstrual
cycles permanently?
Most women stop having menstrual cycles—that is, they reach meno-
pause—between the ages of 45 and 55. It is assumed that a woman has
reached menopause and can no longer become pregnant when she has not had a menstrual period
in 12 months and there is no other biological cause for this.
Why does menopause happen and how long does it last?
Menopause is a natural part of aging. The ovaries gradually stop working, they stop releasing eggs,
and monthly bleeding stops. After reaching menopause, women are no longer at risk of pregnancy
because they do not produce eggs. The transition to menopause occurs when certain hormonal
changes take place in the body. These changes cause irregular menstrual cycles—more or fewer
days of menstrual bleeding and changing cycle lengths. The transition to menopause—from the
time that menstrual cycles start to become irregular to the time that a woman has her last menstrual
period—takes an average of four years.
Hygiene During Monthly Bleeding
What can a woman use during monthly bleeding to absorb the blood?
Women can use homemade or commercial menstrual products
(see illustration on left). They can use pieces of cotton cloth, which
are either placed on a woman’s undergarment or on a homemade
belt that wraps around the waist. These cloths can be washed,
dried, and used again. Commercial products include pads, tam-
pons, and cups. Menstrual pads also are placed on a woman’s
undergarment or come with belts that wrap around her waist. They
are thrown away after they are used. Tampons are shaped like
cylinders and may be available in different thicknesses for light
to heavy fl ow. A woman inserts a tampon into the opening of her
vagina. A tampon has a string at the end so that a woman can pull
it out of her vagina. A menstrual cup can also be inserted into the
vagina. It collects blood but does not absorb it. Some cups can be
reused, and others are meant for one-time use. They are made
from either silicone rubber or pure gum rubber—similar to the
material used to make baby bottle nipples.



How often should menstrual products be changed?
Each woman decides for herself what is comfortable. Menstrual cloths or pads should be changed at least three to fi ve
times a day, but more frequent changes may be necessary. The cloth or pad should be changed before it is soaked with
menstrual blood. If using menstrual cloths, the woman should wash used cloths as soon as possible and dry them com-
pletely before reuse. Tampons should be changed often, at least every four to eight hours. Reusable menstrual cups are
emptied two to four times a day and sterilized by placing them in boiling water for about fi ve minutes. Single-use cups can
be worn for up to 12 hours and then thrown away.
How often should a woman wash her genital area during monthly bleeding?
A woman should wash the genital area at least once a day. This practice, along with changing menstrual pads or cloths
before they are soaked with blood, can help avoid problems such as genital itching and burning during urination.
Bleeding Changes With Contraceptive Use
Which contraceptive methods can change monthly bleeding?
The copper IUD, combined hormonal methods (such as
combined oral contraceptives, monthly injectables, the
vaginal ring, and the contraceptive patch), and progestin-only
methods (such as progestin-only pills, progestin-only
injectables, implants, and the hormonal IUD) all can change
monthly bleeding.
What kinds of changes to bleeding patterns
can these methods cause?
Bleeding changes can range from heavier or longer monthly
bleeding to lack of bleeding to bleeding or spotting at unex-
pected times during the monthly cycle. Different methods
typically cause different changes. (See the last fi ve questions
at the end of this section.) Also, the Lactational Amenor-
rhea Method (LAM)—breastfeeding in a way that reliably
postpones the return of fertility—delays the return of monthly
bleeding after childbirth.
Is there danger in these changes? Are they
signs that some serious problem
is developing?
No. Bleeding changes related to contraceptive methods are
not harmful. They are not signs of illness. They do not mean
that a serious health problem is developing.
Can anything be done if the bleeding changes bother a woman using these
contraceptive methods?
Changes to monthly bleeding occur most often in the fi rst few months of using these methods. Sometimes just knowing
that they are not harmful and are likely to lessen can be reassuring to a woman. Some kinds of bleeding changes can be
treated. If at any time a woman is not satisfi ed and wants to stop the method, she can switch to a method that better
suits her.
Are there contraceptive methods that make bleeding shorter, lighter, and more regular, or
that can be used to treat menstrual problems such as heavy bleeding and cramps?
Yes. Combined hormonal methods, which contain both estrogen and progestin hormones, usually make monthly bleed-
ing lighter, shorter, more regular and predictable, and less painful. These methods include combined oral contraceptives,
monthly injectables, the patch, and the ring.
Which contraceptive methods are most likely to cause heavy or prolonged bleeding?
Heavy or prolonged bleeding occasionally happens with progestin-only pills and implants. This also is common in the fi rst
few months of using an injectable or IUD, but with these methods it usually lessens over time.
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Which methods are most likely to cause infrequent or no monthly bleeding?
Infrequent or no monthly bleed-
ing is common with progestin-
only pills, progestin-only inject-
ables, and the hormonal IUD.
These bleeding changes also
occasionally happen with
combined oral contraceptive
pills, implants, and combined
(monthly) injectables.
Which methods are
most likely to cause
bleeding at unexpected
times during the
monthly cycle?
Unexpected bleeding or spot-
ting happens sometimes with
combined oral contraceptive
pills, progestin-only pills, inject-
ables, implants, and IUDs. It is
most common during the fi rst
few months of use and usually
lessens or stops with time.
Are there any contracep-
tive methods that do not
change menstrual bleed-
ing patterns?
Yes. Male and female steriliza-
tion and barrier methods (male and female condoms, diaphragms, and spermicides) are contra-
ceptive methods that do not change menstrual bleeding patterns. Also, fertility awareness-based
methods, such as the Standard Days Method and the TwoDay Method®, do not change menstrual
bleeding patterns.
Menstrual Problems
What if a woman suddenly stops having monthly bleeding?
Women do miss a monthly bleeding once in a while, and this is not harmful. It could be caused by
stress, minor illness, or weight loss, and sometimes it happens for no apparent reason. Missing a
monthly bleeding is most common among girls in the fi rst two to three years after periods start and
among women nearing menopause. If a woman normally has regular monthly bleeding and then
misses one, however, it could mean that she is pregnant if she had unprotected sex or was not
using a contraceptive method correctly and consistently. She should look for other signs and
symptoms of early pregnancy, such as frequent urination, morning nausea, or fatigue, and see a
health care provider if she thinks that she could be pregnant. Also, some hormonal contraceptive
methods cause infrequent monthly bleeding or stop bleeding altogether. This is normal and not
harmful. It is not likely to be due to pregnancy if the woman has been using her method correctly
and consistently.
What if a woman has monthly bleeding only a few times a year?
This may be due to stress, intense exercise, weight loss, inadequate nutrition, or because she is
nearing menopause. A mild imbalance in a woman’s hormone levels also can cause her to have
no monthly bleeding sometimes. If her normal bleeding pattern changes and she has no monthly
bleeding for several months, and the change is not related to contraceptive use, pregnancy, or
menopause, she should see a health care provider.



What if a woman is bleeding more than usual?
If a woman is bleeding for longer than eight days or is bleeding twice as much as usual for her, she should see a health
care provider. Women usually bleed for two to seven days and lose between 10 ml to 35 ml of blood per cycle. In practi-
cal terms, each woman should be aware of what is normal for her. She can count how many menstrual cloths or pads she
usually uses during monthly bleeding over a few months to determine what is typical for her.
What if a woman has spotting in between monthly bleeding?
Some women bleed a little during the middle of their cycles, around the time when the egg is released from the ovary. This
is nothing to worry about. Combined oral contraceptive pills and progestin-only pills may cause spotting. This, too, is not
harmful. If a woman who is not using such a method has spotting or bleeding at other times than mid-cycle, she should
see a health care provider, especially if after menopause or if she is approaching menopause.
What causes menstrual cramps?
Menstrual cramps happen during monthly bleeding when the lining of the womb breaks down
and the womb contracts to help the blood leave the body. Cramps are one of the most com-
mon menstrual problems that women face. Cramps are more severe or last longer for some
women than for others.
Are there ways to manage menstrual cramps?
Nonsteroidal anti-infl ammatory drugs (such as ibuprofen and aspirin) can help ease the
pain of menstrual cramps. Heating pads or hot water bottles and warm baths also can help
soothe the pain, as can moderate exercise.
What is premenstrual syndrome (PMS)?
PMS is a group of symptoms that some women have one to two weeks before
their monthly bleeding starts. These symptoms can include mood swings,
breast soreness, bloating, acne, cravings for certain foods, increased hunger
and thirst, and fatigue. The symptoms usually disappear within a few days
after the start of a woman’s monthly bleeding.
Are there ways to manage PMS?
The best way to deal with symptoms of PMS is to exercise, eat a
variety of healthy foods, get enough rest, and avoid caffeine, salty foods,
and stressful situations. Some medications might help, such as diuretics
(medicines that increase urination) to help get rid of extra fl uid in the body or
combined oral contraceptives.
When should a woman see a health care provider for bleeding problems?
A woman should see a health care provider if:

• She has not started monthly bleeding by age 16.
• Her monthly bleeding pattern changes suddenly. (However, it is normal for users of hormonal contraceptive

methods and copper IUDs to have changes in their bleeding patterns after starting their method, especially in the

fi rst several months.)

• Her monthly bleeding has stopped suddenly, and this is not a normal effect of a contraceptive method that she
is using.

• She has severe pain during her monthly bleeding.

• She has bleeding after sex.

• She bleeds for longer than eight days.

• She loses twice as much blood as she usually does.

• She bleeds at unexpected times (more than just a few drops outside of regular monthly bleeding), especially if she is
getting close to menopause and is not using a hormonal contraceptive method.

• Her monthly bleeding is far apart (more than 35 days apart in adult women or more than 45 days in adolescents).

• Her monthly bleeding is close together (less than 24 days apart in adult women or less than 21 days
in adolescents).

• She is using a copper IUD and has infrequent or no monthly bleeding. (This is not common with copper IUD use and
probably not related to the IUD.)

• She is using combined oral contraceptives and she has heavy or prolonged bleeding. (This is not common with
combined pills and probably not related to the pills.)
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The links included in this report were up-to-date
at the time of publication.
Abnormal uterine bleeding in adolescents.
Obstetrics and Gynecology Clinics of North
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America 30(2): 321–335. Jun. 2003.
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secretion during lactation and the relationship
Characteristics and determinants of postpartum
to suckling and the resumption of fertility in

ovarian function in women in the United States.
breastfeeding women. Human Reproduction

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4. CRONIN, T.J. Infl uence of lactation upon
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the “Subject” line to [email protected]
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Companies, Mar. 2005. 1600 p.
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6. FLUG, D., LARGO, R.H., and PRADER, A.
a prospective study. British Medical Journal
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7. FRANZBLAU, N. and WITT, K. Normal and
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J., Nelson, A.L., Stewart, F.H., Cates, W.
Bloomberg School of Public Health,
Jr., Guest, F., and Kowal, D. Contraceptive
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Technology. 18th ed. New York, Ardent Media,
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INFORMATION CENTER. Menstruation and
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faq/menstru.htm>. United States Department of
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Health and Human Services, Jul. 25, 2006.
of breastfeeding and lactational amenorrhea:

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14. PRIOR, J.C. Very heavy menstrual fl ow.
Factors associated with the length of
Reports, “When Contraceptives
amenorrhea. Fertility and Sterility 70(3): 461–
Change Monthly Bleeding”
very_heavy_menstrual_fl ow.shtml>. Centre for
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