Ovulation occurs when the ovaries release an egg for potential fertilization. This normal part of menstrual function occurs about 10-14 days into a menstrual cycle, and is followed by an often notable rise in body temperature. Temperature and ovulation are often linked thanks to the fact that ovulation marks the most fertile period of the month for a woman; some women keep track of body temperature and ovulation to help determine the most likely time for pregnancy to occur.
The combination of hormone shifts and the egg release cause the rise in temperature just after ovulation. Some medical professionals believe that a slightly higher body temperature is more hospitable to a fertilized egg, allowing it to implant and begin growth in a more comfortable and suitable environment. It is important to note that women do not usually feel feverish or extremely hot despite the temperature rise; in most cases the increase is so slight, it is not noticeable without daily temperature monitoring.
The practice of linking temperature and ovulation to measure fertility is known as basal body temperature charting or BBTC. The method requires a woman to measure her resting body temperature each day, generally first thing in the morning. In most woman, resting body temperature will rise about .3-.5 degree Fahrenheit (.2-.4 Celsius) immediately after ovulating, and remain elevated until menstruation occurs. While this method does not predict when a woman will ovulate, it can indicate when ovulation has just occurred by the sudden jump in body temperature.
To use BBTC, it is important to get an accurate thermometer that reads out to at least one-tenth of a degree in either Fahrenheit or Celsius, as well as an easily usable charts. To make a chart, use graphing paper to create a graph with days of the cycle running horizontally and temperature running vertically. Day one should be the first day of menstruation. Charts are also easy to find online in downloadable form. Some fertility websites even have online logs that can keep track of BBT for a woman and help keep data on temperature and ovulation.
Most women ovulate around the 14th day of a cycle, but stress, illness, and certain medications may alter this pattern. Some woman have a naturally longer or shorter cycle as well. The idea of the chart is to use it for several months, establishing a pattern of temperature and ovulation that may help predict periods of high fertility. While not 100% accurate, this can give a good general idea of fertility levels.
Some women use this method of measuring temperature to predict ovulation to help get pregnant, but others use it to help avoid sexual intercourse during ovulation to prevent pregnancy. Other methods that are useful in measuring fertility include cervical mucus examination, as vaginal discharge tends to become slick and slippery during ovulation. While neither method is foolproof, combined they can give a woman a fairly accurate idea about her menstrual cycle.