The role of letrozole in in vitro fertilization treatment: new remedy or old mirage?

Aromatase inhibitors, particularly letrozole (LZ), are now established as first-line ovulation induction agents, offering an effective ovarian stimulation strategy to enhance outcomes of intrauterine insemination. In recent years, they have also emerged as potentially valuable adjuvants to gonadotropin ovarian stimulation for in vitro fertilization, particularly in fertility preservation in women with estrogen-responsive cancers. Their primary mechanism of action is to reduce the circulating estrogen levels by inhibiting androgen aromatization. Recent studies have provided evidence that this property may confer therapeutic advantages in other patients undergoing in vitro fertilization. In this study, evidence supporting the role of adjuvant LZ in poor responders, as a moderator of ovarian hyperstimulation syndrome symptoms, and an agent for improving the luteal phase after ovarian stimulation is reviewed. The use of LZ for endometrial preparation in the frozen-thawed embryo transfer cycle is also considered.