The human menstrual cycle is a hormonally regulated

Day Number One of the female reproductive, or menstrual, cycle is defined as the day on which bleeding, and shedding of the uterine lining, begins. This phase is known as menstruation and it is an obvious signal that conception has not taken place. Twenty years ago, it was not possible for a woman to be aware that she was pregnant until her menstrual period was at least two weeks late or longer if her cycles were irregular. At this point, her pregnancy would be defined as being six weeks along.

The human menstrual cycle occurs in three phases, the first of which is the follicular phase. This is defined by the first day of menstruation and occurs just before release of the egg or ovum. Levels of follicle-stimulating hormone (FSH) go up causing the formation of several ovarian follicles, each containing an egg. When FSH levels go down, one remaining follicle continues to develop. As well as housing an egg, the follicle begins to produce estrogen, another female reproductive hormone.

In the second phase, ovulation, levels of a third hormone, leutenizing hormone (LH) are at their highest. The follicle releases the egg and estrogen levels are at their highest level. Once the ovum has been released, the remaining follicle undergoes closure and transformation into a body known as the corpus luteum. The corpus luteum starts to secrete the fourth hormone, progesterone. Together, estrogen and progesterone now work in tandem to cause the lining of the uterus to become thick and ready to nurture the potential products of conception.

Fertilization may take place up to twelve hours after the egg is released. Conception is more likely to occur if sperm are already resident in the reproductive tract prior to release of the ovum. If conception does not take place, the thickened lining is not required to nourish the fertilized egg or zygote, and the lining is discharged during Day 1 of the next menstrual cycle.

There are several methods by which a woman may be able to determine if she is ovulating. One method is to conduct a test using a kit she can purchase from a pharmacy. There are two types of tests. One tests the levels of LH in the urine. The other is an indirect method of detecting estrogen in saliva.

The increased concentration of estrogen causes the saliva to be saltier than any other time during the cycle. When a sample of saliva is left to dry, crystals of salt are deposited on the surface of a glass slide to render a fern-like pattern when viewed under the microscope. Saliva-based kits basically contain a tiny microscope with which to view this salivary ferning and let the woman know that she is fertile.

There are two other ovulation symptoms that do not involve a trip to the drug store, although they should not be relied upon, especially if the aim is to avoid conception. These are sharp, short lasting abdominal pains called 'Mittelschmerz'. The other is to notice the appearance of the normal cervical mucous. Most of the time, this is thick and cream-colored. During the fertile period, it changes into a clear and stringy substance. By understanding when she is likely to be her most fertile, a woman can choose to have or not to have intercourse, depending on whether or not she wishes to conceive.