What is OvulationOvulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg) that participates in reproduction. Ovulation also occurs in the estrous cycle of other animals, which differs in many fundamental ways from the menstrual cycle. When the egg has nearly matured, the level of estradiol in the body has increased enough to trigger a sudden release of luteinizing hormone (LH) from the anterior pituitary gland. In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary, causing the fully developed follicle to release its secondary oocyte.The secondary oocyte promptly matures into an ootid and then becomes a mature ovum. The mature ovum has a diameter of about 0.2 mm.
Which of the two ovaries—left or right—ovulates appears essentially random; no known left/right co-ordination exists. Occasionally, both ovaries will release an egg; if both eggs are fertilized, the result is fraternal twins.
After being released from the ovary, the egg is swept into the fallopian tube by the fimbria, which is a fringe of tissue at the end of each fallopian tube. After about a day, an unfertilized egg will disintegrate or dissolve in the fallopian tube.
Fertilization by a spermatozoon, when it occurs, usually takes place well inside the fallopian tubes. A fertilized egg immediately begins the process of embryogenesis, or development. The developing embryo takes about three days to reach the uterus and another three days to implant into the endometrium. It has usually reached the blastocyst stage at the time of implantation.
In some women, ovulation features a characteristic pain called mittelschmerz (German term meaning middle pain) that may feel like abdominal cramps. The sudden change in hormones at the time of ovulation sometimes also causes light mid-cycle blood flow.
Fertile Window
The most fertile period (the time with the highest likelihood of pregnancy resulting from intercourse) covers the time from some 5 days before until 1–2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week. However, few cycles are exactly average, and what was average for one woman in her early adulthood, may not be the same number once she matures further. A variety of methods have been developed to help individual women estimate the relatively fertile and the relatively infertile days in the cycle: these systems are called fertility awareness.
Fertility awareness methods that rely on cycle length records alone are called calendar-based methods. Methods that require observation of one or more of the three primary fertility signs (basal body temperature, cervical mucus, and cervical position) are known as symptoms-based methods. Urine test kits are available that detect the LH surge that occurs 24 to 36 hours before ovulation; these are known as ovulation predictor kits (OPKs). Computerized devices that interpret basal body temperatures, urinary test results, or changes in saliva are called fertility monitors.
A woman's fertility is also affected by her age. As a woman's total egg supply is formed in fetal life, to be ovulated decades later, it has been suggested that this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life.
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