[Ovulation induction by means of letrozole].
BACKGROUND
Clomiphene citrate is a first line treatment of infertile anovulatory women. Although the treatment induces ovulation in most women, only one in four achieve uncomplicated pregnancy after treatment over several cycles. During recent years several clinics have started to use letrozole tablets for ovulation induction. This paper gives a short presentation of letrozole, mechanisms of action are explained, and pros and cons of letrozole versus clomiphene citrate are discussed.


METHODS
The paper is based on more than two years of clinical experience with use of letrozole for ovulation induction before timed sexual intercourse or intrauterine insemination and the use of letrozole during ovarian stimulation for in vitro fertilization. In addition, a non-systematic search in Pubmed has been performed to give an overview of what is known about letrozole for ovulation induction.


RESULTS
Use of letrozole is associated with a higher chance of uncomplicated pregnancy and a lower risk of multiple pregnancy than clomiphene citrate. In addition, more than 60 % of the women who are resistant to clomiphene citrate ovulate after treatment with letrozole. Letrozole combined with gonadotropin may also be beneficial in some women during in vitro fertilization.


CONCLUSIONS
Studies of letrozole use in reproduction have so far been promising. However, large randomized studies are warranted before it can be concluded that letrozole should become a first line treatment for ovulation induction.
Ekerhovd
Erling
E
Kvinneklinikken Førde sentralsjukehus 6807 Førde og London Fertility Centre 112A Harley Street London W1G 7JH. erling.ekerhovd@obgyn.gu.se
D047072:Aromatase Inhibitors / Q000008:administration & dosage* / Q000009:adverse effects; D002996:Clomiphene / Q000008:administration & dosage / Q000009:adverse effects; D004965:Estrogen Antagonists / Q000008:administration & dosage / Q000009:adverse effects; D005260:Female; D005300:Fertility Agents, Female / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D000077289:Letrozole; D009570:Nitriles / Q000008:administration & dosage* / Q000009:adverse effects; D010062:Ovulation Induction / Q000379:methods; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D012307:Risk Factors; D016896:Treatment Outcome; D014230:Triazoles / Q000008:administration & dosage* / Q000009:adverse effects
D047072:Aromatase Inhibitors; D004965:Estrogen Antagonists; D005300:Fertility Agents, Female; D009570:Nitriles; D014230:Triazoles; D002996:Clomiphene; D000077289:Letrozole