Your basal body temperature and identifying ovulation

Basal body temperature and ovulation

After ovulation, the corpus luteum (the remains of the follicle that released the ovum or egg at ovulation), produces the heat-inducing hormone progesterone. Progesterone causes your resting body temperature to rise after ovulation. Because progesterone is only secreted in high amounts after ovulation has occurred, it is possible to pinpoint ovulation as occurring on the day before your temperature rises when your temperatures are plotted on a graph.

Biphasic pattern

A fertility chart that shows ovulation detected by a rise in basal body temperature (BBT) will have a biphasic pattern. This means that your chart will show lower temperatures before ovulation, a rise in temperature (thermal shift) and then higher temperatures after ovulation. 

Ovulation usually occurs on the last day of lower temperatures.

The rise in temperature is usually about 0.4 degrees Fahrenheit or 0.2 degrees Celsius, but the rise may be as slight as 0.2 degrees Fahrenheit or 0.1 degrees Celsius or even less in some cases. The actual temperatures are less important than noting a biphasic pattern showing two levels of temperatures.

So, to summarise a biphasic chart pattern will show low temperatures before ovulation, ovulation occurring and then higher temperatures after ovulation.

Basal body temperature and ovulation

Your basal body temperature is your body temperature at rest as measured in the morning, after at least three hours of sleep and before you get up measure using a special basal body temperature thermometer.

Your temperature sign is the sign that will best help you to precisely pinpoint the day that ovulation occurred. This is because progesterone, and hence your temperature, increases quite dramatically just after ovulation has taken place.

The rise in your basal body temperature is the only sign that that you can observe on your own that can confirm that ovulation occurred. All the other signs (including OPK’s) only tell you that ovulation may be approaching.

No pregnancy

If there is no pregnancy, your temperature will stay elevated for 10 to 16 days, until the corpus luteum regresses. Unless there is a pregnancy, progesterone levels drop dramatically, and you get your period. Your temperature normally drops as well, though it is not unusual to have erratic or high temperatures during your period.

Temperature shift and conception/pregnancy

Your basal body temperature rise can tell you when you have ovulated, but it will not tell when you are most fertile in a current cycle. This is because your fertile days are the 2 days before ovulation and the day of ovulation (your fertile window).

Once your basal body temperature has shifted, it is too late to conceive in that cycle as the fertile time has already passed. So, while measuring your basal body temperature can help to pinpoint or confirm ovulation, it is important to observe this sign in conjunction with other signs as well, particularly your cervical fluid (to identify your fertile window). Observing multiple signs allows for cross-checking in the case that one sign is ambiguous or affected by other factors.