The final critical steps during the weeks just prior to ovulation (the release of the egg) are controlled by ultra-specific instructions delivered from the pituitary gland in the brain to the ovary. The ovary is responsible for nurturing a healthy egg. The pituitary send messages continuously to the ovary in waves, much like a melody. If the "melody" is out-of-tune or some "notes" are missing, the result will be a subtle flaw in the egg. The brain "singing" an off-tune melody to the ovary accounts for many instances of infertility and miscarriages. Appropriate infertility treatment can harmonize this song from the pituitary to the ovary.
The following is an illustration of how things might go amiss in the development of an oocyte. Consider that the brain communicates with the ovary through molecular messages delivered via the bloodstream from specific sites in the brain to the ovary. The two messages that appear to be the most important in the development of an oocyte are Follicle Stimulating Hormone ( FSH) and Luteinizing Hormone (LH). These two hormones are assembled in the Pituitary Gland, but the instructions for the production, storage, and release of FSH and LH arise in a nest of cells in the Hypothalamus called the Arcuate nucleus.
The Arcuate nucleus resides in community with other hypothalamic nuclei (B through J). These nuclei control impulses related to life-promoting appetites for water, calories, sleep, physical growth, the pleasure of physical intimacy, an optimal body temperature, etc. Hypothalamic nuclei B-J have their own agendas but, because of their proximity to the Arcuate nucleus, they may influence the availability of an oocyte that is perfect or ‘optimal’.
The ‘perfect’ oocyte, then, is the consequence of the ovary’s response to a symphony delivered from the brain via the circulation. FSH does what its name implies…the physical growth of the ovarian follicle or “incubator” containing a single chosen oocyte of the month, bathed in estrogen enriched water. FSH though obviously essential, seems a little lackluster, perhaps like a percussionist. The first violin in the “musical” would be LH. It provides the “beat” in the music that arrives at the ovary, its rhythmic secretion from the pituitary is like a musical score intended to gather attention and excitement. Every 2 to 2 1/2 hours a “pulse” of LH arrives at the follicle to reassure those cells surrounding and nurturing the oocytes that all seems fine. Then, because of its very short half-life, the LH almost disappear from a woman’s circulation only to reappear in 2 1/2 hours in a “just-right” concentration.
What might alter the secretion of LH? Some causes would be obvious such as inordinate leanness. Other explanations may be too subtle to know for certain. For example, some hypothalamic nuclei are supposed to be up-regulated by sleep while others are down-regulated. The pattern of LH secretion under the control of the Arcuate nucleus during the maturation of an oocytes, should remain the same whether a woman is awake or asleep. Physicians consider it plausible that some women have altered or absent LH pulses during sleep. It is also clear that it would be impractical to pursue the confirmation of this or similar disorders in every woman whose conception is delayed for reasons not apparent. If such a problem is suspect, brief trials of experience-tested employment of pharmaceuticals is warranted.