An ovulation calendar helps women to predict their most fertile days for getting pregnant. The day on which ovulation occurs is the most fertile day of the month. Knowing when this period of improved fertility happens can allow a woman to time her sexual intercourse in order to increase her chances of getting pregnant. It also allows a woman to take the appropriate birth control measures to avoid pregnancy. During a typical 28 to 32 day menstrual cycle, ovulation peaks between days 11 and 21; fertility typically begins five days before ovulation.
To understand how the ovulation calendar works, it is necessary to understand the process of ovulation. Ovulation takes place at about the halfway mark of the menstrual cycle. The hypothalamus in the brain signals the pituitary gland, which begins secreting special hormones, called follicle-stimulating and lutenizing; these hormones "tell" the ovaries to release the eggs, which then travel down the fallopian tubes to be fertilized by sperm. The eggs travel to the uterus for implantation, if fertilized, or to be eliminated from the body as menstrual discharge.
There are certain signs that indicate the beginnings of ovulation. The cervical mucus thickens due to the increasing concentrations of estrogen. Body temperature may increase slightly in response to the increased levels of hormones that trigger the release of eggs by the ovarian follicles. The two or three days leading up to the rise in body temperatures are considered the fertility peak. A few ovulating women may also report mild pain or cramping.
Many free ovulation kits and ovulation calendars can be found online. Three criteria are necessary to establish an ovulation calendar: the date of the last period; length of the period; and the luteal phase, when luteinizing hormones are secreted. On average, the luteal phase takes place 14 days from the day of the last period for a woman maintaining a 28-day cycle, 15 days later for a woman on a 29-day cycle, or 16 days later for a woman on a 30-day menstrual cycle.
To use an ovulation calendar, a woman should track the last few months of her menstrual cycles to establish a pattern. Once a pattern has been established, the calendar can be used to predict the day of the next period, as well as the best days to conceive children of a particular gender. This theory, which is known as the Shettles Method, postulates that if conception occurs close to the ovulation date, a male child is the likely result. If conception occurs two to three days before ovulation, a girl will be conceived.
An ovulation calendar works best for those women with menstrual cycles within the 28 and 32 day period. Ovulation charts are affected if menstrual cycles occur outside of the norm, or if the luteal phase progresses beyond 16 days or begins less than nine days from the start of the menstrual cycle. It is also important to note that ovulation does begin right at the middle of a woman's cycle, occurring instead between days 9 and 17. With such unpredictability, an ovulation calendar may not be the most effective method to establish fertility.