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Knowing Your Circle
Fertility Cycle:
Your body prepares for pregnancy during the menstrual cycle, when
changing hormone levels cause the ovaries to release an egg that
can be fertilized. A typical menstrual cycle lasts about 29 days.
After the first week or more, estrogen levels in the blood begin
to rise to prepare the uterus for possible implantation of an egg.
It is expected that women also get a surge of their chloride ion
levels during this time. That surge comes approximately 6 days before
ovulation. This is followed by a surge of luteinizing hormone (LH)
that triggers egg release (ovulation) in the following 12-24 hours.
These events are shown on the graph below. (Note: click the graph
to enlarge it.)
The fertility cycle has 3 phases: the follicular phase, ovulation,
and the luteal phase.
Follicular phase (pre-ovulation)
During this first phase (the start of the cycle), the pituitary
gland in your brain sends a signal to one of your ovaries to get
ready to release an egg. After receiving this signal, a fluid-filled
sac called a follicle develops and the follicle eventually produces
a mature egg. The follicle also releases estrogen, which prepares
cervical mucus to receive the male sperm. Eventually one dominant
follicle will release a surge of estrogen telling the pituitary
it has an egg and is ready for ovulation.
The number of days in the follicular phase can vary among women
and from month to month. This is what can make determining ovulation
particularly challenging. Because of this, ovulation cannot always
be determined by counting forward from the start of your menstrual
cycle.
Ovulation
This mid-cycle phase is when your pituitary receives the estrogen
signal from your follicles. At this time, a large amount of leutinizing
hormone (LH) is released. This surge of LH signals the follicle
to release the egg. About 12 to 24 hours after the LH surge, ovulation
takes place. The egg then makes its way from your ovaries to your
fallopian tubes and then towards the uterus, where sperm can fertilize
it.
Luteal phase (post-ovulation)
In this last phase, which lasts on average for 14 days, the follicle
becomes a corpus luteum and progesterone is produced. Progesterone
is a hormone that is needed to prepare your uterus for a fertilized
egg. It is also what causes breasts to become tender, mood swings,
and bloating or water retention, all symptoms of premenstrual syndrome
(PMS).
At this point, a fertilized egg imbeds itself in the wall of the
uterus and pregnancy occurs. If the egg is not fertilized it will
disintegrate within about 12 hours. Progesterone levels then drop
and the lining of the uterus is shed, resulting in menstruation
and the start of another fertility cycle.
Understanding Male Fertility
There are many factors that influence male fertility. Each man should consult his doctor for a thorough
analysis of his reproductive health but some of the actions and behaviors to avoid when trying to conceive are listed below.
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Hot tubs, saunas (or anything that raises the temperature of your scrotum, including overheated vehicles and hot work environments) |
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Smoking (smoking significantly decreases both sperm count and the liveliness of sperm cells) |
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Prolonged use of marijuana |
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Use of other "recreational" drugs (e.g., cocaine) |
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Chronic alcohol abuse |
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Use of anabolic steroids (which can cause testicular shrinkage and infertility) |
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Overly intense exercise (excessive exercise may lower your sperm count by producing higher levels of adrenal steroid hormones, which lower the amount of testosterone in the body. This testosterone deficiency, in turn, decreases sperm production) |
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Tight fitting clothes such as briefs or elastic exercise clothing |
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Excessive stress |
Age Considerations
What you've heard about age and fertility is true-as a woman ages, her ability to conceive declines. This gradual decline in fertility starts very subtly in the late 20s to age 35 but then becomes more pronounced as age approaches 40 and older. In one French study, researchers found that the pregnancy rate over one year for women younger than 31 was 74%. For women between the ages of 31 and 35 the rate declined to 62% and to 54% for women beyond 35 years of age. In another study, 87% of women age 45 and older were no longer able to bear children. But the ticking of the biological clock is not as inexorable as it once seemed. Medicine and technology are developing ways for women to improve their chances of conceiving. This article will try to explain not only why fertility declines with advancing age but also how assisted reproductive technology can improve a woman's chances of becoming pregnant.
The reasons for the decreased fertility rate with age is multi-fold. Many women, married or unmarried, are waiting longer before attempting pregnancy. As sexually active women grow older, the likelihood that they might be exposed to sexually transmitted infections increases. These infections (such as chlamydia or gonorrhea) can permanently scar the pelvic organs which can hinder a woman's ability to become pregnant. The chance that a woman might experience fertility related complications from endometriosis or adenomyosis (disorders which involve uterine lining cells-endometrial cells-implanting in abnormal locations in the pelvis) increases with age as well.
One of the most important explanations for age-related infertility in women is the declining number of genetically
normal available eggs. The peak number of eggs (also known as oocytes) is achieved long before women even consider
becoming pregnant: when a female fetus is 4-5 months old, still in the mother's uterus, it possesses up to 6-7 million
eggs. By birth, this number drops to 1-2 million and declines even further when, at the start of puberty in normal girls,
there are 300,000-500,000 eggs. Several hundred oocytes are lost during the 3-4 decades a woman has regular menstrual
cycles through the monthly development and ovulation of an oocyte. Many other oocytes are lost through triggered, natural
cell death. When a woman reaches her mid- to late 30s, when she has about 25,000 eggs left in her ovaries, the loss rate
of oocytes accelerates. In addition, as a woman ages the ability of her oocytes to divide and distribute the genetic
contents normally declines. The likelihood that an oocyte with an abnorm al number of chromosomes will be fertilized
increases with age. Older women (particularly over the age of 35) have a gradually increasing risk of pregnancies which are
genetically abnormal. Most of these genetically abnormal pregnancies are miscarried in the first or second trimester of
pregnancy. Unfortunately, older women (again older than 35 and especially past the age of 40) have a higher risk of
miscarrying even genetically normal pregnancies. Several studies have found that for women over 40, the overall risk of
miscarrying a pregnancy is about 75%.
Assisted reproductive technology--using "fertility drugs" in conjunction with artificial insemination or in vitro
fertilization--may enhance an older woman's ability to conceive. Using injectable (or, in some cases, oral) medications,
a woman can increase the number of available oocytes which mature and are then available for fertilization. With
artificial or "intrauterine" insemination, a doctor can insert sperm directly into the uterus and time it according to
when the oocytes are mature. Although the overall pregnancy rate achieved with medications and insemination is around
14-17%, the success rate falls to less than 10% for women over 40. With in vitro fertilization (also known as IVF), a
woman uses injectable hormones to stimulate her ovaries after which a doctor extracts the mature oocytes using a
minimally invasive procedure. In the lab, the extracted oocytes are mixed with sperm or even directly injected with
individual sperm. If embryos develop from this in vitro fertilization process, they are t hen transferred into the
woman's uterus. The pregnancy success rate for IVF can be as high as 50-70% in women in their 20s or early 30s and
though the success rate declines with age, some centers achieve success rates over 20% for women in their early 40s.
Unfortunately, not all 40-year-old (or even 30-year-old) women respond to fertility treatments in the same way. By
measuring two hormone levels-- estrogen and follicular stimulating hormone (FSH)--on the third day of a woman's
menstrual cycle, a doctor can assess the likelihood that a woman may respond to stimulation. Elevated estrogen and/or
FSH levels (and the values vary from lab to lab) may indicate a decline in normal, available oocytes. A woman with
abnormal day 3 hormone levels possesses a much lower likelihood of responding well to fertility treatments as well as
a lower chance of becoming pregnant when compared to a woman of the same age with normal estrogen and FSH levels. For
a woman with persistently elevated FSH levels and/or who has not responded well in past IVF cycles, donor egg is the
last option. With donor eggs, a young donor (usually less than 35) is stimulated, her eggs are retrieved, fertilized
with the sperm of the infertile woman's partner, and the resultant embryos are placed in th e older patient's uterus.
Even women in their late 40s or 50s can attain a pregnancy success rate of greater than 40-50% with donated eggs.
The one caveat is that all these scientific explanations of aging and fertility are not absolute. There are anecdotal
accounts of women in their 40s having failed multiple IVF cycles who then become pregnant without assistance. Turning
40 does not mean a woman can no longer bear children, only that she might need medical assistance (and possibly someone
else's eggs) along the way.
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