Ovulation, the release of an egg from the ovary, is necessary for conception to occur. Approximately 0-40% of infertile women have ovulatory problems. Often ovulation is induced with the aid of medications. The process is called ovulation induction.
Who is a candidate for ovulation induction?
Medications can be used to stimulate ovulation in women who rarely or never ovulate (anovulation) and to treat women who have no menstrual cycles (amenorrhea). They can also be used to increase the frequency of ovulation in women who ovulate infrequently. Medications are sometimes prescribed to treat luteal phase defect, a condition in which the second half of the menstrual cycle is shortened and the uterus is not properly primed to receive an embryo. These medications are also used to stimulate multiple egg development in order to enhance the success rate of assisted reproductive procedures such as IVF.
The most commonly used medication to induce ovulation is clomiphene citrate (trade name Clomid®). Clomiphene is taken for five consecutive days early in the menstrual cycle. Clomiphene works by “fooling the body” into thinking estrogen is low; certain hormones are then released which cause egg development. Letrozole (trade name Femara®) is another medication used to induce ovulation. Like clomiphene, this medication is taken for five consecutive days early in the menstrual cycle. Letrozole is an aromatase inhibitor which prevents the conversion of androgens into estrogen. By blocking the production of estrogen, the body is again fooled and there is a release of hormones which causes follicular development. When follicles are mature the body will respond to the mature egg with an LH surge, or the use of HCG (human chorionic gonadotropin, trade names Novarel®and Ovidrel®) will trigger the release of an egg and ovulation will occur. Insemination or timed intercourse will be scheduled after ovulation.
Human follicle stimulating hormone (FSH, trade names Bravelle®,Gonal F®, Follistim®) and Human menopausal gonadotropin (hMG, trade names Menopur® and Repronex®), are injectable medications given over a period of 5-12 days to produce growth and maturation of ovarian follicles, which contain eggs. The dose used to produce maturation of the follicles is individualized for each patient and may vary from cycle to cycle. Response to the medication (follicle number and size) is monitored with the use of blood estrogen levels and ultrasounds. When follicles are of the appropriate size and an appropriate estrogen level is achieved, ovulation is usually triggered with the use of hCG (human chorionic gonadotropin, trade names Novarel®and Ovidrel®) so that intercourse, insemination or egg retrieval may be timed.
GnRH analogs (Lupron®, Antagon®, Cetrotide®) are synthetic hormones similar to gonadotropin releasing hormone (GnRH), which is released by the brain to control the pituitary gland. Normally a rhythmic release of GnRH stimulates the pituitary to secrete FSH and LH, the hormones needed to cause egg production and ovulation. When a synthetic GnRH analog is given, the opposite effect occurs. Lupron® causes an initial increase in FSH and LH and the subsequent suppression of these hormones. Antagon® and Cetrotide® cause immediate suppression. The use of GnRH analogs in conjunction with gonadotropins allows for better hormonal control of ovulation induction and fewer canceled cycles.
Outcome with GnRH Analogs
In IVF cycles, GnRH analogs are used routinely to enhance egg production and to prevent spontaneous ovulation. The use of these medications has significantly lowered the cancellation rate for all assisted reproduction cycles by at least 75%. The use of GnRH analogs for ovulation induction that is not being performed in conjunction with assisted reproduction is also sometimes used. This is especially the case in older women who may not be as sensitive to the effects of gonadotropins alone.
Hormonal therapy with a variety of medications can temporarily correct ovulatory problems and increase a woman’s ability to become pregnant. Your physician will discuss all the specific indications for usage, physiology, side effects and risks associated with these medications.
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