Basal Body Temperature

Basal body temperature is your body’s temperature prior to rising from bed and after having rested for a minimum of three hours. This can vary slightly from one woman to another. Increasing levels in the hormone progesterone result in a slight increase in body temperature of approximately 0.2 C degrees Celsius following ovulation. This increase may be smaller of greater and can be seen as either a sudden increase or a more gradual climb over several days. An increase in body temperature does not predict ovulation but rather signals that ovulation has already occurred. Once your body temperature peaks and remains at this higher level for three days you can conclude that ovulation has occurred. This temperature increase continues throughout your cycle until immediately prior to the onset of menstruation when it will dip slightly, however if you are pregnant your temperature will remain elevated.

The Basal Body Temperature method involves measuring your body temperature each morning prior to rising, plotting these temperature readings on a chart and examining the resulting patterns. As you see changes from month to month you will gradually build up an overall picture of your fertility pattern. By including other fertility indicators with your charting this should provide you with an even more detailed understanding of your menstrual cycle and fertility patterns.


Obtaining a thermometer

A digital basal body temperature thermometer or an accurate digital thermometer is recommended as these are easier to read and will 'beep' to let you know when your temperature has been accurately recorded. You should use the same thermometer throughout a cycle.

There are a number of manufacturers that produce thermometers especially suited for charting basal body temperatures. Typically these have a finer range, increased sensitivity measuring up to 1/100th of a degree and specialised memory features. Baby 4 You are stockists of the flexi style, high accuracy, 1/100 degree scale, auto beep OuvTemp basal body thermometer.

Taking your temperature

Prior to going to bed in the evening leave your thermometer within arm's reach of your bedside. As soon as you wake up (and before doing anything else) take your temperature according to the directions given with your particular thermometer.

You can take your temperature orally, vaginally or rectally so long as you take in same place for the duration of your cycle. You should take your temperature as close as possible to the same time each day, as your temperature can vary with time (0.1 C per hour)

Recording your temperature

Record your temperature and date either directly onto your BBT chart or onto a piece of notepaper to add into your chart or charting software latter in the day. BBT thermometers often come with a complementary blank chart that be easily photocopied. Our flexi basal thermometer comes with such a chart or you might like to download our alternative version for free.

Download our Free Basal Body Temperature Chart Here

There are a number of excellent websites that specialise in providing online charting options and software. Our personal favourites are www.fertilityfriend.com www.fertility.webmd.com and www.ovusoft.com. If you have a personal favourite which you would like to recommend please feel free to email us and we will add it to our list.


Interpreting your results

After plotting your results examine your chart for a temperature shift of at least .2 C over a 48-hour period to indicate ovulation. Ideally this thermal shift should be above the highest temperatures you have recorded in the previous six days. Some women also experience a slight dip in temperature when they ovulate. You are most fertile and most likely to get pregnant during the two to three days just before your temperature hits the highest point.