Extended Letrozole Regimen Versus Clomiphene Citrate for Superovulation in Patients With Unexplained Infertility Undergoing Intrauterine Insemination

Unexplained infertility is one of the most frequent infertility diagnoses encountered by the gynaecologists . Several studies reported that 10 to 20% of infertile couples have unexplained infertility .

Superovulation and intrauterine insemination (IUI) is an effective treatment for couples with unexplained infertility . Superovulation increases the probability of pregnancy by increasing the number of oocytes suitable for fertilization or by correcting any subtle defect in ovulation . Furthermore, IUI increases the concentration of active motile sperms reaching the fallopian tube and overcomes male factors or cervical factors of infertility not detected by conventional tests .

For more than four decades , clomiphene citrate has been the first line therapy used for induction of ovulation in women with anovulatory infertility and for superovulation in couples with unexplained infertility, mild endometriosis and mild male factor of infertility . Clomiphene citrate is cheap , orally administered , requires no frequent monitoring and associated with very low risk of high-order multiple gestation and severe ovarian hyperstimulation syndrome . However , clomiphene citrate causes long lasting depletion of estrogen receptors and therefore exerts antiestrogenic effect on estrogen target tissues as endocervical mucosa and endometrium .Several studies revealed the clomiphene citrate has a deleterious effect on cervical mucous quantity and quality and endometrial development resulting in endometrial thinning , luteal phase defect ,decreased uterine flow and implantation failure .

During the past decade, letrozole (aromatase inhibitor approved by FDA for the treatment of postmenopausal women with breast cancer ) has been successfully used in induction of ovulation in anovulatory patients with polycystic ovary syndrome and in augmentation of ovulation in ovulatory women . In contrast to clomiphene citrate , letrozole is rapidly eliminated from the body and does not deplete estrogen receptors and therefore has no antiestrogenic effects on endometrium or endocervical mucosa .

Several studies revealed that letrozole can be used as an alternative to clomiphene citrate for superovulation in patients with unexplained infertility . A metaanalysis of seven randomized controlled trials comparing aromatase inhibitors ( letrozole or anastrozole ) with clomiphene citrate in patients with unexplained infertility revealed that the pregnancy rate was comparable between both management options .