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ORDER
Clomid
is often the first fertility drug prescribed by the
physician. In order to understand how Clomid works,
a brief overview of the female reproductive hormone
system is necessary.
The hypothalamus is a small gland located
at the base of the brain, which serves as the "coordinator"
or "thermostat" for various reproductive
hormones. Follicle stimulating hormone, gonadotropin
releasing hormone, estrogen, and luteinizing hormone
are the most important for ovulation. The hypothalamus
releases gonadotropin-releasing hormone, which stimulates
the pituitary to produce FSH. FSH directly stimulates
the ovaries and causes follicular (each follicle contains
one egg) recruitment and development.
As the follicles develop, they produce
rising levels of estrogen that are monitored by the
hypothalamus. As estrogen increases the hypothalamus
signals the pituitary to reduce production of FSH
and stop follicular recruitment. Once the eggs mature,
the hypothalamus signals the pituitary to produce
luteinizing hormone, which stimulates ovulation of
the egg.
Clomid works at the hypothalamus to
cause increased production of gonadotropin releasing
hormone (GnRH) thus causing the pituitary to produce
more FSH. Clomid "competes" for estrogen
binding sites at the hypothalamus. Once Clomid binds
to the estrogen receptors, the hypothalamus will "read"
lower estrogen levels than actually exist causing
increased GnRH release and more FSH production.
It is important to note that Clomid
establishes normal ovulation using the body's natural
production of FSH. Other products (FSH) stimulate
the ovaries directly causing development of many follicles.
Clomid is taken as prescribed usually
at 50 mg beginning on the third, fourth, or fifth
day of the menstrual cycle. Once regular ovulation
is occurring, there is no advantage to increasing
the Clomid dose. This is because once the estrogen receptors
are saturated; the pituitary cannot produce additional
FSH.
Numerous studies show that Clomid
is most likely to work during the first three ovulatory
cycles and treatment beyond six cycles is rarely effective.
Infertility specialists will quickly move to FSH when
pregnancy is not established within these time frames.
Continued use of Clomid beyond six cycles can lead to increased
side effects.
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