Ovulation is the release of a mature egg, or ovum, from the ripe follicle of an ovary.
There are three primary phases to ovulation:
- Periovulatory (follicular) phase: Cells surrounding the ovum increase in volume and produce mucous; the lining of the uterus (endometrium) begins to thicken
- Ovulatory (ovulation) phase: Secretion of enzymes from the follicle create a hole through which the ovum leaves the ovary and enters the fallopian tubes. This is a 2 to 4 day span of time in which fertilization is possible.
- Postovulatory (luteal) phase: Secretion of luteinizing hormone (LH) from the empty follicle (or corpus luteum) enhances and maintains the endometrial lining of the uterus. A fertilized ovum, or zygote, will implant in the endometrium, while an unfertilized ovum will be shed with the lining during a menstrual period.
The menstrual cycle lasts on average 28 to 32 days, with the first day being the first day of your period. Ovulation occurs approximately 10 to 14 days after the last day of your period, or on the fourteenth day of your cycle. It can, however, occur as early as the fifth or as late as the nineteenth day.
Every month, one to several follicles, which each contains a single ovum (also known as an oocyte, or egg), begins to mature within one of your ovaries. As a follicle matures, it releases estradiol, a form of estrogen that acts upon the hypothalamus in the centre of the brain. In response, gonadotropin-releasing hormone (GnRH) released by the hypothalamus stimulates the release of hormones from the anterior lobe of the pituitary gland. These include follicule stimulating hormone (FSH) and luteinizing hormone (LH). Rising levels of LH and FSH stimulate increases in number and changes in the mucosal secretions of the cells surrounding the ripening ovum, and in your cervix. These changes facilitate fertilization. The acidic mucous provides an environment around the egg and in the reproductive tract that enables sperm mobility and survival.
LH induces the production of enzymes that break down proteins in the follicle of the ovary. This creates a hole (the stigma), allowing the ripe ovum to be released into the peritoneal cavity, where it is caught by the finger-like fimbriae of the fallopian tubes. Once trapped in the fimbriae, the ovum travels into your fallopian tubes towards the uterus. During this time it can be fertilized by a sperm. If fertilization occurs, the ovum becomes a developing zygote, which normally implants in the endometrial lining of your uterus 6 to 10 days afterwards. (Congratulations! You’re pregnant!) If not, it will degrade within about twenty-four hours and be shed with the endometrial lining of the uterus, resulting in a menstrual period and marking the beginning of the next cycle.
After the ovum is released, the empty follicle collapses on itself to form the corpus luteum. This mass of cells continues to produce estrogen and progesterone. These act on the endometrial glands of the uterus to develop and maintain the endometrial lining. The surge in progesterone creates a rise in basal body temperature (BBT) of 0.4 to 1.0 degree Fahrenheit (about 0.3 to 0.5 degree Celcius).
Signs to look for
There are distinct signs that you can look for to indicate ovulation and peak fertility. Changes in cervical mucous are easily visible, as it tends to become thick, clear, and “stretchy”. At this time it feels and looks much like egg white. A sharp and sustained rise in basal body temperature (BBT), as described in the periovulatory phase, is another good indicator. Greatest fertility is about 48 to 72 hours the before maximum is reached. Tracking BBT on a daily chart is one of the most common methods used to predict the time of ovulation. Finally, elevated levels of LH can be detected using urine test kits and used to help pinpoint the timing of ovulation.
For some women, ovulation is accompanied by mild discomfort, aching or a sharp pang in their abdomen. This is called Mittelschmerz, German for “middle pain.” It may last only a few moments or as long as several hours. You may experience a stronger sense of smell; this increases your ability to detect the sex pheromones of your mate. Similarly, you also release pheromones that are powerful attractants to the opposite sex.
Around this time you also may experience heightened sexual arousal and desire before ovulation. Studies have shown that women’s faces appear more attractive during this stage; and that women are more attracted to men with stronger masculine attributes and behaviors. These changes are evolutionary mechanism made, of course, to increase your chances of becoming pregnant.