What is the most likely etiology of infertility in a 24-year-old female with dark hair growth along her chin and jawline, and a history of irregular menstrual cycles?

The most likely etiology of infertility in this case is Polycystic Ovary Syndrome (PCOS). This condition is characterized by a combination of irregular menstrual cycles, signs of hyperandrogenism (such as hirsutism, which is indicated by the dark hair growth along the chin and jawline), and polycystic ovarian morphology on ultrasound.

The irregular menstrual cycles suggest anovulation, which is a common feature of PCOS due to hormonal imbalances affecting ovarian function. The presence of hirsutism is also significant, as it often indicates elevated androgen levels, another hallmark of PCOS.

While endometriosis, hypothalamic amenorrhea, and uterine fibroids can contribute to infertility, they do not explain the combination of symptoms presented here as well as PCOS. Endometriosis typically presents with pelvic pain, and hypothalamic amenorrhea is usually associated with significant weight changes or stress. Uterine fibroids, while they can lead to fertility issues, do not typically account for hyperandrogenic features like hirsutism. Therefore, the clinical presentation strongly aligns with PCOS, making it the correct etiology for infertility in this scenario.