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Dr. C Sharath Kumar, Prof and Head, Dept. of Reproductive Medicine and Surgery, Mediwave Institute of Medical Science, Mysore 22 January 2025
The process of ovulation can be described as follows: Between the 6th and 14th day of the menstrual cycle, FSH causes follicles to grow in one or both ovaries. During the 10-14th day of the menstrual cycle, one or more developing follicles form a fully mature egg. Around the 14th day, a sudden luteinizing hormone (LH) surge occurs, leading the ovary to release this egg.
Phases of the Menstrual Cycle:
· Menstruation
· Follicular Phase
· Ovulation
· Luteal Phase
During the Ovulatory Phase, the hormones LH and Estrogen peak, and there is a mild surge in FSH, while the Progestogen level sees no escalation until the luteal phase.
The LH’s signal transduction cascade initiates the ovulatory phase, which activates the pro-inflammatory genes through the cAMP secondary messenger.
Other events of the ovulatory phase include – secretion of proteolytic enzymes by the follicles, follicular tissue degradations, stigma formation; departure of the secondary oocyte, which commutes to the peritoneal cavity through stigma, the secondary oocyte attaches to the fimbriae at the end of the fallopian tube; the secondary oocyte enters the fallopian tube, the oocyte is pushed along with cilia and starts to move towards the uterus.
Ovulation is initiated by LH and FSH surge. LH stimulates egg release (ovulation) – 16 to 32 hours after the hormonal escalations. An egg only survives for 12-24 hours after ovulation. If fertilization by a sperm fails during this window, the body reabsorbs the egg.
The hypothalamus of the brain controls ovulation – through LH and FSH release. Further, FSH is also functional in cumulus expansion (a series of transformations in the ovarian follicle) in the preovulatory phase. Ovulation is initiated by the gonadotropin-releasing hormone (GnRH) – secreted by the hypothalamus. GnRH triggers FSH and LH secretions by the pituitary gland.
After ovulation, the egg is available for fertilization – the luteal phase. The uterine lining (endometrium) is thickened and prepared to receive the fertilized egg. If no fertilization occurs, the endometrium and the egg are shed during the menstrual phase.
The Fertile Period
The days of maximum fertility can be predicted based on the date of a woman’s last menstrual period and the length of a typical menstrual cycle. Typically, days 10-18 (after menstruation) of the menstrual cycle – a few days surrounding ovulation, constitute the most fertile phase––in a regular 28-day menstrual cycle. The commencement date of the last menstrual period (LMP) until ovulation spans 14 days, on average. The prediction interval (window period of fertility) is 8-20 days in a 28-day menstrual cycle – with a 95-percentile prediction interval.
The estrogen level peaks towards the end of the follicular phase, which causes a positive feedback mechanism for about 12-24 hrs – for the LH surge and FSH release (Ovulatory Phase). The LH and FSH surge lasts 24-36 hrs and causes ovarian follicle rupture and oocyte release. Ovulation can also be triggered by low-dose HCG inj. after a completed cycle of ovarian stimulation.
Signs of Ovulation: Changes in cervical mucus, basal body temperature, heightened sense of smell, tender breasts, bloating, greater sexual desire, and cramps.
Oligoovulation is infrequent or irregular ovulation and anovulation is the absence of ovulation. Menstrual disorders often indicate an ovulatory impairment; other ovulation disorders include:
· WHO group I – Hypothalamic-pituitary-gonadal axis failure
· WHO group II – Hypothalamic-pituitary-gonadal axis dysfunction, the most common
· WHO group III – Ovarian failure
· WHO group IV – Hyperprolactinemia
Drugs that can treat ovulation disorders are – Metformin, Dopamine agonists, Clomiphene, and Letrozole. When all these drugs fail, gonadotropin treatment can be considered.
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