Induction of Ovulation With Clomiphene Citrate: Mode of Action, Indications, Benefits, Limitations and Contraindications for its use

Clomiphene (Clomid, Serophene) is by far the most widely prescribed agent for the induction of human ovulation for women who do not ovulate, those with dysfunctional ovulation and women with ”unexplained” infertility. When used in young women (who have adequate ovarian reserve) with these problems the viable pregnancy rate is reported as being between 6% and 10% per cycle of treatment. Aside from conventional ovulation induction, clomiphene has been used in preparing women for intrauterine insemination and even for IVF. I personally rarely prescribe clomiphene because across the board, success rates are significantly lower than when gonadotropin therapy is used. The main reasons for clomiphene’s popularity is its low cost, simplicity of use and the low risk of dangerous complications such as severe ovarian hyperstimulation syndrome (OHSS).Clomiphene treatment can be initiated at a dose of 50 mg (orally) daily for 5 days but it can be increased to as much as 200mg per day, starting on cycle 2, 3, 4, or 5. A spontaneous LH surge will usually follow within about 8-9 days of the last 50mg dosage. In some cases, 10,000U of hCG can be given as a trigger when there is at least one ovarian follicle of 18-20 mm in size. Routinely using the hCG trigger does tend to decrease pregnancy potential. Clomiphene works by inducing ovulation through its “antiestrogen effect” which, by blocking estrogen receptors in an area of the brain known as the hypothalamus, tricks the brain into “thinking” that estrogen levels are low. In response, the hypothalamus prompts the pituitary gland to release an exaggerated amount of follicle-stimulating hormone (FSH), which in turn stimulates the growth and development of ovarian follicles, ultimately resulting in a surge in the release of pituitary LH. About 38-42 hours later, ovulation occurs from one or more of the larger follicles. As the follicles grow, they release more and more estrogen into the bloodstream, thus closing the feedback circle that the hypothalamus initiated in response to the anti-estrogen properties of Clomiphene.There are several factors that need to be considered carefully before deciding to prescribe clomiphene to any woman:

• Clomiphene citrate therapy is less effective than gonadotropin therapy and its efficacy declines with advancing age: Many infertile couples undergoing ovulation induction believe that the success rate using clomiphene citrate is equivalent to what we see in fertile couples trying to get pregnant on their own and to what is encountered when gonadotropins (Menopur/Follistim/Gonal-F and Puregon) are used. This is not the case. The truth is that the rate of conception with clomiphene therapy is actually about 30% lower than the natural fertility rate for normally ovulating women, and about 25% lower than when gonadotropin stimulation is used for ovarian stimulation in similar patients. Moreover, the discrepancy is further magnified with advancing maternal age, where in women under 35 years, the pregnancy rate with clomiphene treatment is about 10% per cycle, about 5% between 35 and 40 years and <2% for women in their early to mid-forties.

• Clomiphene use should ideally be confined to younger women: Ideally the use of clomiphene should in my opinion be restricted to younger women (under 35 years) who have normal “ovarian reserve” (as assessed by basal blood FSH, and antimullerian hormone (AMH) levels). These are the women who are most likely to respond by producing multiple follicles. It is necessary that at least 3 sizeable follicles (>15mm) develop on clomiphene treatment, in order to override the “anti-estrogenic” effects of this drug and so insure adequate cervical mucus production as well as the development of a receptive endometrium.

• Clomiphene should usually not be administered for more than 3 consecutive (back-to- back) cycles: If used back-to-back for more than 3 consecutive cycles, clomiphene is not only ineffective, but actually starts to function as a “relative” contraceptive! This is often is a shocking revelation to many women. Clomiphene’s anti-estrogenic effect is not confined to the hypothalamus. Any cells that have a high concentration of estrogen receptors will also be so affected. Needless to say, the cervical glands (that produce estrogenic mucus to facilitate sperm transport and the endometrial lining (endometrium) that thickens under the effect of estrogen are also highly vulnerable to a buildup of antiestrogen effects over successive back-to back cycles of clomiphene therapy. This why with >3 consecutive back-to back clomiphene cycles cervical mucus tends to thicken and dry up and the endometrium will thin, seriously reducing the likelihood of success. These anti-estrogenic manifestations require that following 3 back-to back clomiphene cycles of stimulation there be at  least 1 resting (non-clomiphene treated) cycle, before doing a 4th cycle.

• Clomiphene should not be used in older women or in women who have diminished ovarian reserve (DOR): With clomiphene stimulation, the  release of pituitary FSH is always accompanied by the concomitant release of Luteinizing Hormone (LH). LH causes the ovary to produce male hormone (androgens) and testosterone. The production by the ovaries of a modest amount of testosterone would not present a problem. However, an excessive production of ovarian testosterone prejudices egg development and thus ultimately compromises embryo competency. Older women and women with DOR are the most vulnerable because they tend to have overgrowth of ovarian connective tissue (stroma/theca) which is the site where androgens are produced. The concentration of androgens is always much higher at the site of production (the ovaries) than in the peripheral blood (a dilution effect). Thus in older women and those with DOR, there will be excessive ovarian androgens that can compromise egg quality and thus ultimately reduce the chance of having a baby. The older the woman and/or the more severe the DOR, the greater this adverse effect is likely to be.

• “Trapped” ovulation (LUF-Syndrome): About 20% of clomiphene cycles are associated with “trapped” ovulation (Luteinized Unruptured Follicle (LUF) Syndrome). This means that in spite of hormone changes suggesting that ovulation has occurred, the egg remains trapped in the ovary. Obviously this is not condusive to the establishment of a successful pregnancy.

• Endometriosis is a “relative contraindication” to the use of clomiphene: Women with endometriosis (regardless of its severity) have” toxic factors” in their pelvic peritoneal fluid. Eggs, as they pass from the ovaries to the Fallopian tubes to reach the awaiting sperm, become exposed to these “toxins” which renders the egg envelopment (zona pellucida) resistant to sperm penetration. This reduces fertilization potential by a factor of at least 3 or 4. This means that if, in the absence of endometriosis, an egg has a 15% chance of being fertilized and thereupon resulting in a baby, that same egg, in a woman with endometriosis would have no more than a 5% chance. Thus, if the overall chance of a having a baby per year of actively trying is about 12% then the chance in a woman with mild endometriosis (of the same age) would probably be no more than 3-4%. This serves to explain why normally ovulating women with endometriosis and patent Fallopian tubes do not benefit significantly from intrauterine insemination, with or without the use of fertility drugs, or from surgery to remove endometriotic lesions (since many endometriotic deposits are non-pigmented, thus invisible to the naked eye and cannot be removed surgically). Only IVF improves the chance of a baby per month of trying.  Simply put…if a normally ovulating woman who has mild to moderate endometriosis conceives following IUI, surgery, or the use of fertility drugs, it is probably in spite of (rather than due) to such treatment.

• Women with long gaps between menstruation are often not ideal candidates for clomiphene: Women who consistently have  >45 days between their periods will not respond well to clomiphene induction of ovulation and are better off going directly to injectable gonadotropins.

• Multiple pregnancy: The incidence of multiple pregnancies with clomiphene induction of ovulation is about 5%. This is much lower than the 25% rate encountered when gonadotropins are given to women with absent or dysfunctional ovulation.

Clomiphene therapy is often used as a first line approach to inducing ovulation in women with irregular or absent ovulation such as in women with polycystic ovarian syndrome (PCOS). Its use in my opinion is best confined to women who menstruate/ovulate irregularly (but who bleed at least every 45 days), younger women, women who do not have tubal disease or endometriosis, women under 40 years of age (preferably <35y), and women who do not have DOR . It should also be avoided when there is co-existing male factor infertility.  If pregnancy fails to occur after 3 consecutive cycles of clomiphene therapy, then in my opinion, it is time to move on to gonadotropin therapy, combined with IUI or IVF/ICSI depending on the underlying cause of the infertility.