This clinical trial, sponsored by The University of Hong Kong, aims to compare the hormonal profiles and follicular development between Letrozole and Clomifene Citrate in women with Polycystic Ovary Syndrome (PCOS) and ovulatory women with unexplained subfertility. Given the prevalence of PCOS affecting 5-10% of women of reproductive age, successful outcomes could position Letrozole as a more favorable first-line treatment compared to Clomifene, particularly due to its associated lower multiple pregnancy rates. The trial's findings may influence treatment guidelines and market dynamics, potentially increasing the adoption of Letrozole in fertility treatments, which could impact the competitive landscape for existing ovulation induction therapies.