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A menstrual cycle of 14–21 days is shorter than the typical average and falls outside the normal range for most women. This condition is known as polymenorrhea and can be caused by various factors, including hormonal imbalances, stress, or underlying medical conditions. While it occurs, it is not considered the average duration.

A cycle of 35–45 days is longer than the normal range. This is known as oligomenorrhea and can be caused by hormonal disturbances, such as polycystic ovary syndrome (PCOS), or other endocrine disorders. While it can occur in some individuals, it is not representative of the average cycle duration.

A menstrual cycle lasting 45–60 days is significantly longer than the normal range and is indicative of oligomenorrhea or amenorrhea. This prolonged cycle length often suggests significant hormonal dysfunction or anovulation. It is not a typical duration for a healthy, regular menstrual cycle.

Luteinizing hormone (LH) is primarily responsible for triggering ovulation, not the initial growth of the follicles. While LH is present during the follicular phase and acts synergistically with FSH to promote estrogen synthesis, its levels surge around day 14 of a typical cycle, leading to the rupture of the dominant follicle and the release of the oocyte. This LH surge is a key event marking the end of the follicular phase and the beginning of ovulation.

Progesterone is the dominant hormone of the luteal phase, which occurs after ovulation. Its main function is to prepare the uterine lining for implantation by increasing its vascularity and glandular secretions. It is secreted by the corpus luteum, the remnants of the ruptured follicle, and its levels are low during the follicular phase, making it incorrect as the stimulus for follicular growth.

Estrogen is produced by the growing follicles in response to FSH stimulation, not the other way around. Estrogen levels rise progressively during the follicular phase, and this increasing concentration has several effects, including the proliferation of the uterine endometrium and a positive feedback loop on FSH secretion, which eventually leads to the LH surge. Therefore, estrogen is a product of follicular growth, not its primary stimulant.

Progesterone levels are low during the follicular phase, with a normal range of 0.1 to 0.7 ng/mL. It is produced in significant amounts by the corpus luteum after ovulation. Its primary role is to prepare the uterine lining for implantation and maintain pregnancy, and its rise is a consequence of the LH surge, not the cause. Therefore, high progesterone levels do not trigger the LH surge.

Follicle-stimulating hormone (FSH) levels are not low when the LH surge is triggered. In fact, there is a small, but significant, concurrent surge of FSH that is also caused by the high estrogen levels. The LH surge and this FSH surge both contribute to the final maturation of the oocyte and the process of ovulation. Low FSH would not support follicular development to the point where high estrogen levels could be produced.

Gonadotropin-releasing hormone (GnRH) levels do not drop before the LH surge. Instead, the high estrogen levels trigger a surge in GnRH from the hypothalamus, which in turn stimulates the anterior pituitary to release the LH surge. This is a positive feedback loop, where the high estrogen promotes more GnRH and LH secretion, leading to the cascade of events that result in ovulation.