The Menstrual Cycle: Overview
What is ovulation?
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When a young woman reaches puberty, she begins to ovulate - a process in
which a mature egg cell (also called an ovum), ready for fertilization by
a sperm cell, is released from one of the ovaries (two female reproductive
organs located in the pelvis). If the egg is fertilized by a sperm cell
as it travels down the fallopian tube, then pregnancy occurs and it becomes
attached to the lining of the uterus until the placenta (an organ, shaped
like a flat cake, that only grows during pregnancy and provides a metabolic
interchange between the fetus and mother) develops. If the egg does not
become fertilized as it travels down the fallopian tube on its way to the
uterus, the endometrium (lining of the uterus) is shed and passes through
the vagina (the passageway through which fluid passes out of the body during
menstrual periods; also called the birth canal), a process called menstruation.
As the average menstrual cycle lasts 28 days (starting with
the first day of one period and ending with the first day of the next
menstrual period), most women ovulate on day 14. At this time, some women
experience minor discomfort in their lower abdomen, spotting, or bleeding,
while others do not experience any symptoms at all.
A woman is generally most fertile (able to become pregnant)
a few days before, during, and after ovulation.
What is menstruation?
Menstruation is one part of a woman's menstrual cycle which includes the
shedding of the endometrium (lining of the uterus) that occurs throughout
a woman's reproductive life. With each monthly (on average) menstrual cycle,
the endometrium prepares itself to nourish a fetus, as increased levels
of estrogen and progesterone help to thicken its walls. If fertilization
does not occur, the endometrium, coupled with blood and mucus from the vagina
and cervix (the lower, narrow part of the uterus located between the bladder
and the rectum) make up the menstrual flow (also called menses) that leaves
the body through the vagina.
When does menstruation begin?
On average, menarche (a young woman's first menstrual period) occurs between
the ages of 12 and 14 years old - generally two years after her breast budding
(average age 10 to 12 years old), and, in most cases, not long after the
onset of pubic hair (average age 12 years old) and underarm hair. Stress,
various types of strenuous exercise, and diet can affect the onset of menstruation
and the regularity of the menstrual cycle.
The American College of Obstetricians and Gynecologists
recommends that a young woman consult her physician if she has not started
to menstruate by the age of 16, and/or if she has not begun to develop
breast buds, pubic hair, or underarm hair by the age of 13 or 14.
How long is a menstrual cycle?
For menstruating women, an average menstrual cycle lasts 28 days - starting
with the first day of the last period (which, on average, lasts six days,
with some women having a very light flow and others having a very heavy
flow) and ending with the first day of the next menstrual period. However,
the length of women's cycles varies, particularly for the first one to two
years after menarche (a young woman's first menstrual period). Women may
have cycles as short as 23 days, or as long as 35 days. However, anything
that deviates from this range is considered abnormal and may require medical
attention.
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