Definition: In this task, you are given an abstract of article. Your task is to generate title for this article. Preferred titles are under thirty words.
Input: OBJECTIVE To compare pregnancy rates (PR) for letrozole and gonadotropins in individuals who failed to conceive with clomiphene citrate (CC).   
 DESIGN Retrospective cohort study.   
 SETTING University reproductive center.   
 PATIENT(S) Individuals treated with letrozole or gonadotropins who failed to conceive with CC.   
 INTERVENTION(S) Controlled ovarian hyperstimulation (COH), transvaginal ultrasound, ovulation induction, IUI.   
 MAIN OUTCOME MEASURE(S) Pregnancy rates per cycle.   
 RESULT(S) Among patients who failed to conceive with at least three cycles of CC, gonadotropins had a higher PR per cycle than letrozole. Among individuals who failed to conceive with less than three cycles of CC and whose medications were changed because of thin uterine lining or intolerable side effects, average PR per cycle for letrozole and gonadotropin treatments were equivalent. All patients conceived within three stimulation cycles with either gonadotropins or letrozole.   
 CONCLUSION(S) In patients who failed to conceive with CC, gonadotropins have higher PR for ovulation induction than letrozole. However, PR were high enough with letrozole to justify its use in this population of patients. Letrozole and gonadotropins should not be used for more than three cycles without a conception.

A comparison of letrozole to gonadotropins for ovulation induction, in subjects who failed to conceive with clomiphene citrate.