MENSTRUAL CYCLE AND PREGNANCY
Although the period of the human menstrual cycle can vary from 20 to 35 days,
the average cycle lasts for 28 days. During this time, the female reproductive
system carries out the processes of the menstrual cycle, which occurs in phases.
The menstrual cycle begins in females at puberty, which takes place between
the ages of 10 and 16. It will continue until a woman reaches menopause, at
which time the ovaries stop releasing mature eggs. This occurs between the ages
of 40 and 60.
Did you know that when a baby girl is born, she has all the eggs her body will
ever use, and many more, perhaps as many as 450,000? They are stored in her
ovaries, each inside its own sac called a follicle. As she matures into puberty,
her body begins producing various hormones that cause the eggs to mature. This
is the beginning of her first cycle; it's a cycle that will repeat throughout
her life until the end of menopause.
The hypothalamus is a gland in the brain responsible for regulating the body's
thirst, hunger, sleep patterns, libido and endocrine functions. It releases
the chemical messenger Follicle Stimulating Hormone Releasing Factor (FSH-RF)
to tell the pituitary, another gland in the brain, to do its job. The pituitary
then secretes Follicle Stimulating Hormone (FSH) and a little Leutenizing Hormone
(LH) into the bloodstream which cause the follicles to begin to mature.
The maturing follicles then release another hormone, estrogen. As the follicles
ripen over a period of about seven days, they secrete more and more estrogen
into the bloodstream. Estrogen causes the lining of the uterus to thicken. It
causes the cervical mucous to change. When the estrogen level reaches a certain
point it causes the hypothalmus to release Leutenizing Hormone Releasing Factor
(LH-RF) causing the pituitary to release a large amount of Leutenizing Hormone
(LH). This surge of LH triggers the one most mature follicle to burst open and
release an egg. This is called ovulation.
The cycle of the moon's phases, or synodic cycle, lasts 29.5 days from new
moon to new moon.The period of the sidereal cycle of the moon, which is the
time it takes for the moon to complete an orbit of the earth, is 27.3 days.
The average of the period of the synodic and sidereal cycle is 28 days, which
is the average period of the human menstrual cycle. This correlation has prompted
some to believe that the moon "controls" the female reproductive system.
In the culture of the ancient Romans, the goddess of the moon, Diana, cared
for women, especially those who were pregnant.
In most cases, the period of the menstrual cycle is predictable after it stabilizes
during the first few years of puberty. This consistency is important to women
because an irregularity in the cycle can signify important changes in a women's
body. For instance, if menstruation does not take place according to the usual
cycle, it could mean that the woman is pregnant. Also, women become familiar
with the period of their menstrual cycles in order to increase the chances of
fertilization. Usually, a woman is most fertile between days 10 and 17 of her
cycle, because during that time, the egg is in the Fallopian tubes.
High Pregnancy Risk of Menstrual Cycle
The egg bursts from the ovary (ovulation) approximately two weeks before the
beginning of your next menstrual period. A common misunderstanding is that the
egg bursts from the ovary at midcycle, halfway between menstrual periods. This
is only true when the cycle is twenty-eight days long (something that cannot
be known for certain until that particular cycle is over and menstruation begins).
A woman can become pregnant from unprotected intercourse up to five days before
ovulation. Sperm can survive in a woman's body for three to five days, waiting
to fertilize that egg during ovulation. Therefore, guessing how long our period
usually is and counting backward fourteen days is not an effective method of
birth control.
The fertility awareness method of birth control (a studied, standardized monthly
procedure), however, can be quite effective if used diligently and properly.
Being aware of your fertile times involves counting days, observing cervical
mucus, taking the body temperature with a basal thermometer (see below for details)
daily, and charting with own observations.
Fertility awareness can be quite effective when taught carefully, understood
thoroughly, and used correctly. The major disadvantages are the risk of pregnancy
if you are not committed to using it correctly; it does not protect from sexually
transmitted diseases (STDs), including HIV infection; it takes at least two
or three cycles to learn and use confidently; it can be sexually frustrating
if we choose to abstain from intercourse rather than use a barrier method when
we are fertile; and, most importantly, it may be impractical if we are not in
a committed, cooperative relationship with oursexual partner.
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