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Basal Body Temperature

Tracking your Basal Body Temperature (BBT) requires a lot of patience and consistency.

Used alone, it may be a difficult way to "predict" ovulation, as the shift in your body temperature occurs after you have ovulated.

However, if you have a very regular period, and see the same pattern month after month, then this method alone, may be good for you.

Tracking your BBT is a good way to "confirm" ovulation or to provide your doctor with information about your cycle if you are having difficulty conceiving.

  • Start each chart on the first day of your period. It is best to track your temperatures, every day. The more data the better. Keep in mind that your temperatures may remain high during your period as you may still have elevated progesterone levels.
  • BBT or Basal Body Temperature is the temperature of your body at rest and should therefore be taken the first thing in the morning before getting out of bed, or doing any activity.
  • The more consistent your environment is, the more reliable your temperature data will be. In any given cycle, your temperature should be taken in the same way, using the same thermometer, as close to the same time as possible. You should have at least 4 hours of solid sleep prior to taking your temperature, and the climate should be kept as consistent as possible. Any variations outside of this, should be noted on your chart when recording your temperature.
  • Medications, OPK and Fertility Monitor results, intercourse, and IVF IUI ICI procedures should be recorded on your chart daily along with your temperature. As discussed later on this page, you may also choose to monitor and record cervical mucus patterns, position and feel of your cervix and saliva ferning patterns. Some women also choose to record symptoms such as backaches, breast tenderness, and bloating.
  • You will need to see your temperature to a tenth (0.10) of a degree. For this reason, you should get a thermometer, specifically designed to measure your BBT. If pressed, you can use a glass fever thermometer and a magnifying glass, but we recommend getting a BBT thermometer.
  • If taking your temperature by mouth, make sure to follow the directions, and put the thermometer in the heat pocket located just under your tongue.
  • Obviously the more regular your period, the easier it will be to detect your ovulation day. But even if your periods are less regular, if you do BBT tracking for a number of months, you may still find that you have certain patterns.
  • If you are ovulating, temperatures at the beginning of your cycle will be lower than temperatures after you ovulate. This is referred to as a BIPHASIC pattern.
  • Some women, will see a distinct temperature dip (or ovulation dip) when they ovulate or ovulate on pretty much the same day every month. If you consistently see this, and have verified it with another method like an OPK, then you may feel comfortable relying on BBT charting alone. Most women, will not see a dip, but will see a temperature rise, and by then it is too late, as ovulation has already occurred. For this reason we recommend using OPKs along with charting.
  • Ovulation generally occurs on the last day of lower temperatures.
  • Your most fertile time is the 2 days prior to ovulation to the day of ovulation. This is because a man's sperm may survive in fertile cervical mucus for up to 72 hours whereas a woman's egg will survive for only 12-24 hours without being fertilized. If you wish to become pregnant, now is the time to begin having unprotected sex.
  • After ovulation, your temperature will rise. Sometimes it will take a few days to see the rise. After an egg is released, the body will produce the hormone progesterone in order prepare the uterus for implantation in case the egg is fertilized. It is the rise in the levels of this hormone that causes your body temperature to rise.
  • The shift occurs when you detect a temperature that is at least 0.2 degrees Fahrenheit or 0.1 degrees Celsius higher than the previous six days. You should wait to see if your temperature remains elevated for at least three days in order to confirm that this is your thermal shift.
  • In order to more easily see the shift, a "coverline" is drawn by drawing a horizontal line across your chart, 0.10 degrees higher than the highest temperature of the 6 days prior to the rise in temperature (you may ignore one days temperature if it is much higher than the rest). You may also choose to draw a vertical line through your ovulation day.
  • Your temperatures should remain above your coverline until the end of your cycle. An elevation of 18 days or more may indicate that your are pregnant. Your temperature may drop for a day or two, but should remain elevated for at least 10 days if you ovulated.
  • Remember that you are looking for a BIPHASIC pattern. There are many kinds of variations after ovulating. Sometimes your temperature may shoot up, sometimes it will shoot up, come down and then gradually go up, sometimes it will step its way up, etc. etc. As long as you can see a biphasic pattern you can comfortably determine when you ovulated.
  • If you do not become pregnant your temperature will remain elevated for 10-16 days. Your hormones will return to pre-ovulation levels causing your temperature to decrease, although you may still see some erratic or high temperatures during your period.
  • If you become pregnant your temperatures will remain elevated for more than 18 days as your body continues to keep progesterone levels high. A sustained elevated temperature is one of the earliest signs of pregnancy.
  • During the two-week wait many women look for any sign to see if they are pregnant. For this reason, many women will chart their symptoms (bloating, painful breasts, etc.) along with their temperature. Unfortunately all of the early pregnancy symptoms are the same as PMS symptoms so there is no definitive symptom that will verify pregnancy.
  • Likewise, there is no particular BBT pattern that shows pregnancy prior to missing your period. Although a TRIPHASIC pattern (a pattern in which there is a secondary rise in temperature) occurs twice as much in pregnancy charts it still occurs frequently in ovulatory charts. This is also true of charts with "implantation dips" or single day dips in temperature between days 5 and 12, which may be caused by the egg implanting in the uterus.
  • If you do not see a distinct BIPHASIC pattern in your cycle after charting for awhile you may wish to consult a physician as you may be having problems ovulating.
  • If you see that you consistently have higher temperatures for less than 10 days, you may also want to cosult a physician as it may indiciate a shortened luteal phase, which would make it difficult for you to maintain a pregnancy without supplemental progesterone.
  • We have provided blank paper BBT Charts for your use. Simply click on the appropriate link below. After the the chart is displayed in a separate window, click on the File browser window navigation choice and then Save As on the File dropdown menu. Once you have saved the file, you may close the chart window. Please note that the chart looks better printed than online and the hole-guides used to create binder holes may not be aligned properly.

    Click Here to Download a Fahrenheit BBT Chart

    Click Here to Download a Celsius BBT Chart