Unlocking the Mysteries of Ovulation and Infertility – ARC Summit
In discussing infertility, it’s important to note that about half of the causes are attributable to female factors, while a third are due to male factors. Additionally, approximately 17% of infertility cases involve both partners contributing to the issue.
A key component to understanding infertility is the ovulatory cycle. It begins with the hypothalamus in the brain, which secretes a peptide called GnRH, a decapeptide consisting of 10 amino acids. GnRH stimulates the pituitary gland to produce the gonadotropins LH (luteinizing hormone) and FSH (follicle-stimulating hormone). These hormones are released approximately every 90 minutes and are crucial for stimulating the ovaries to develop an egg.
Over a two-week period, this hormonal activity leads to the development of an egg in the ovaries. When the egg is mature, an LH surge triggers ovulation. During a normal menstrual cycle, there are fluctuations in hormone levels. For example, during the early part of the cycle, FSH levels are higher than LH, which selects the follicle to mature. For the remainder of the cycle, LH levels are higher, keeping the ovaries relatively inactive and leading to the natural attrition of oocytes.
Women are born with about a million eggs, and by puberty, about 300,000 remain. Each month, between 500 to 1,000 eggs are lost, irrespective of whether a woman is on birth control or pregnant. However, when a critical level of FSH is present, it selects two or three eggs to mature, which can be observed during follicular monitoring via ultrasound.
Post-ovulation, the ruptured follicle transforms into the corpus luteum, which produces estrogen and progesterone for about two weeks. If pregnancy does not occur, the corpus luteum degenerates. This decline is due to the reduced GnRH stimulation, which lowers the frequency of GnRH pulses to about two per day, causing a drop in LH and FSH levels. Consequently, estrogen and progesterone levels fall, the endometrial lining is no longer supported, and menstruation occurs.
If conception happens, the presence of hCG (human chorionic gonadotropin) from the pregnancy maintains the corpus luteum. HCG is similar to LH and binds to the same receptors, preventing the regression of the corpus luteum. If hCG is absent, progesterone and estrogen levels decrease, the endometrial lining is shed, and a menstrual period begins.
