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Fertility Drugs An Overview
Fertility drugs are available to treat many of the conditions that cause infertility.
Many of these fertility drugs, such as Clomid and FSH, are known as "ovulation
inducing agents". A normal menstrual cycle involves
follicular (egg) recruitment and growth, development
of the endometrium,ovulation,
fertilization, and implantation in the endometrium. These processes are regulated by hormone
relationships in the "hypothalamic-adrenal-pituitary
axis (HPA)". Conditions that adversely affect the
HPA axis can lead to anovulation (lack of ovulation)
and infertility. Many fertility tests are available to help determine the cause of failed ovulation.
Fertility drugs which belong to the "ovulation induction" category include Clomid, Letrozole, Gonal-F, Follistim, Bravelle, Menopur, and Repronex. Metformin is a fertility drug which causes ovulation to resume by correcting chronically elevated insulin levels. Other fertility drugs such as Lupron, Ganirelix, and Cetrotide enable the fertility specialist to control the timing of ovulation during assisted reproductive technology cycles.
Fertility Drugs and Ovulation
Many fertility drugs work at the hypothalamus or pituitary gland to influence the production of FSH, LH, and other hormones. It is necessary to have a basic
understanding of how the HPA axis functions in order to understand how these fertility drugs exert their actions and some of the causes of infertility.
The hypothalamus
can be compared to a "thermostat" because
it monitors the levels of hormones such as follicle
stimulating hormone (FSH), luteinizing hormone (LH),
estrogen, and others. As it monitors these hormones,
it "balances" their levels.
Fertility drugs such as Lupron and Ganirelix exert their effects by influencing the production of GnRH. During the first days of the menstrual
cycle, the hypothalamus produces gonadotropin-releasing
hormone (GnRH), which travels to the pituitary where
it stimulates the release of follicle stimulating hormone.
Fertility drugs, such as Lupron and Ganirelex, inhibit GnRH production thus reducing the internal production of FSH and blocking the LH surge. Therefore, FSH must be administered by injection. FSH, used in IVF superovulation, causes the recruitment of follicles, each of which
contains an egg, and supports them as they mature. As
the follicles grow they begin to produce estrogen, which
travels through the bloodstream to the hypothalamus.
Estrogen also helps stimulate endometrial development.
Fertility drugs (FSH) like Gonal-F, Follistim, and Bravelle are administered during an IVF cycle to stimulate the
recruitment and development of numerous eggs, needed
for IVF. Unlike Clomid which works at the hypothalamus ,
FSH stimulates the ovaries directly.
Fertility drugs, such as Lupron and Antagon, influence the actions of GnRH allowing the physician to control the stimulation cycle, particularly when ovulation occurs. Rising levels of estrogen
cause the hypothalamus to reduce its production of
GnRH thus lowering FSH levels. Once the follicle(s)
is mature, the hypothalamus signals the pituitary to
release a surge of LH,
which triggers ovulation.
Fertility drugs such as Pregnyl and Ovidrel are used in IVF cycles to stimulate ovulation since the effects of GnRH are blocked. These products have the same effect on ovulation as LH. The ruptured follicle remaining
after ovulation forms a structure known as the corpus
luteum, which begins to produce progesterone to support
the pregnancy. Once the embryo has implanted, the placenta
begins producing progesterone.
Fertility drugs such as FSH must be monitored to insure proper follicular development and reduce the chance of side effects. The fertility
specialist carefully adjusts the dose of
to insure follicular development and to time ovulation.
In an in vitro fertilization
cycle, ovulation must not occur prior to egg retrieval
or the cycle would be "lost". Lupron and Ganirelex are products that block the LH surge,
albeit by different mechanisms. A women usually will
not ovulate as long as she receives one of these products.
Once the physician judges that the follicles are mature,
an injection of hCG (the fertility drugs Ovidrel, Pregnyl, or Luveris may be used) is given to mimic the natural LH
surge and egg retrieval is scheduled. hCG is available
as Pregnyl, generic, and Ovidrel. Ovidrel, a fertility drug produced by Serono Labs, is pure
hCG derived from genetic recombinant technologies and is identical to the body's naturally produced hCG.
Fertility Drugs- Links
Many fertility drugs are available
to treat infertility. Please select the links below
for more information:
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