Preovulatory

In human reproduction, the preovulatory period is the interval immediately before ovulation. It is part of the follicular phase of the menstrual cycle, during which a dominant ovarian follicle matures in preparation for releasing an oocyte. The term is used in human medicine and veterinary science to describe the phase leading up to ovulation, with timing and hormonal patterns that vary by species. In a typical 28-day cycle, this window spans roughly days 10 to 14, but timing varies among individuals and cycles.

Hormonal regulation: The hypothalamus releases GnRH, prompting the pituitary to secrete FSH and LH. FSH drives follicular growth; as the dominant follicle develops, it secretes increasing amounts of estrogen. Rising estrogen triggers a surge of LH about 24 to 36 hours before ovulation, initiating follicle rupture and oocyte release.

Ovarian events: The mature follicle, or Graafian follicle, prepares to rupture. The oocyte completes meiosis I just before ovulation and is released as a secondary oocyte arrested at metaphase II until fertilization.

Endometrial changes: Estrogen-induced thickening and vascularization of the endometrium prepare the uterus for potential implantation. After ovulation, progesterone from the corpus luteum dominates and supports secretory endometrium; the preovulatory phase is characterized by low progesterone.

Clinical relevance: The preovulatory window is tracked in fertility awareness methods and timed intercourse. Ovulation predictor kits detect the mid-cycle LH surge, signaling the approaching preovulatory phase. In assisted reproduction, clinicians time treatments to align with this window.