Mitwally, M. F., & Casper, R. F. (2004). Aromatase inhibitors in ovulation induction. Seminars in Reproductive Medicine, 22(1), 61-78. https://doi.org/10.1055/s-2004-823028
Mitwally, Mohamed F., and Robert F. Casper. "Aromatase inhibitors in ovulation induction." Seminars in Reproductive Medicine, vol. 22, no. 1, 2004, pp. 61-78.
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2 institutions
Department of Obstetrics and Gynecology, University of Toronto, and The Samuel Lununfeld Research Institute, Mount Sinai Hospital, Toronto, Canada.
More positive pregnancy tests on letrozole than clomiphene, one clinic
A 2004 review from the team that first used letrozole to bring on ovulation, reporting pregnancy results from their own treatment cycles. Letrozole alone gave a positive pregnancy test more often per cycle than clomiphene alone.
Key Findings
From 1999 to 2001 at the authors' Toronto center, 33 of 167 letrozole-alone cycles gave a positive pregnancy test. Clomiphene alone gave 80 of 994 cycles (8%).
Multiple pregnancy occurred in 1 of 23 clinical pregnancies after letrozole alone (4.3%) and in 12 of 55 after clomiphene alone (21.8%).
Total pregnancy loss was 10 of 33 positive tests after letrozole alone (30.3%) and 25 of 80 after clomiphene alone (31.3%).
Adding letrozole to FSH injections cut the FSH dose needed by 45 to 55% in PCOS and unexplained infertility. Pregnancy rates did not differ significantly from FSH alone in either group.
A randomized study the review cites found pregnancy in 16.7% of patients on an aromatase inhibitor and 5.6% on clomiphene (p = 0.55, a nonsignificant difference).
Interpretation
This review reports ovulation induction cycles from the authors' own center. Letrozole suits women with ovulation problems classified as WHO type II, a group that includes polycystic ovary syndrome (PCOS, also called PMOS). Women with WHO type I or III ovulation problems are unlikely to benefit, apart from borderline cases. The authors note their data were not randomized or placebo-controlled and call for randomized trials. The findings support larger, randomized study of letrozole for ovulation induction.
RRM Context
A drug that brings on ovulation targets the missing ovulation. Restorative reproductive medicine also asks why a woman does not ovulate, and examines both partners first. The review reports ovulation augmentation in women who already ovulate and carry the label unexplained infertility. RRM calls that label undiagnosed: the cause has not been found yet.
Our editorial summary of this paper, not the article's abstract.
Abstract
The new third generation aromatase inhibitors are extremely potent and specific oral inhibitors of estrogen production. We reported the success of using aromatase inhibitors for induction of ovulation in World Health Organization (WHO) type II anovulatory patients. Promising pregnancy rates were associated with the use of aromatase inhibitors for induction of ovulation in these women. In addition, the use of aromatase inhibition in conjunction with gonadotropin injection was associated with a significant reduction in the gonadotropin dose required for optimum controlled ovarian hyperstimulation. We believe that these oral agents are efficient and safe and have many advantages compared with clomiphene citrate (CC). We propose that aromatase inhibitors will replace CC in the future as the new primary treatment for ovulation induction. In this review, we present an update on the use of aromatase inhibitors for induction of ovulation and we discuss several new areas of potential interest regarding the use of aromatase inhibitors, either alone or together with recombinant follicle-stimulating hormone (FSH) for infertility treatment. Further research in these areas may demonstrate an expanded role in assisted reproductive technologies.
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