One of the most significant indicators of the time of ovulation during your usual cycle is the ovulation temperature.
At the time of ovulation, your basal body temperature (BBT) will rise – and it will stay a little higher until menstruation.
The phenomenon of ovulation temperature has been a fairly reliable, low tech method for women to chart their normal ovulation cycle since early in the last century.
These days, you can purchase easy-to-use hormone test kits which give a definite indicator of whether you have ovulated.
However, the cost of the test kits can add up, particularly if you are using them over a number of months.
If you are on a tight budget and you are just trying to get an indication of your normal ovulation rhythm, charting your ovulation temperature can give you a good indication of when ovulation has occurred.
Why does ovulation temperature occur?
From adolescence until menopause, most women will experience a rise in their resting body temperature immediately after ovulation, which will remain at that level for the rest of the month.
Immediately after the egg has been released from the ovary, the empty follicle starts to produce a number of hormones designed to prepare your body for a possible pregnancy.
One of these hormones, progesterone, causes your basal body temperature to rise.
Towards the end of the regular cycle, your progesterone levels start to fall again, triggering menstruation.
What is basal body temperature – and how do you measure it?
When your body has been in a state of rest for a period of time, your core body temperature drops to conserve energy.
The best time to measure your basal body temperature is first thing in the morning, when you wake up, ideally before you get out of bed.
To chart your basal body temperature, use an accurate thermometer to take your temperature each morning before you get out of bed and record it manually.
There are a number of thermometers on the market specifically designed to measure your basal body temperature. The main feature of these thermometers is their ability to give accurate and detailed results.
However, the majority of standard digital thermometers will measure temperatures in increments of 0.05°C, so they are quite adequate for charting your ovulation temperature.
You need to take your temperature once a day, every day, at the same time. Ideally, you will chart your basal body temperature over a number of months so that you can get a good idea of the pattern of ovulation temperature that will occur in your own cycle.
Immediately after ovulation has occurred, there will be a very small spike in your basal body temperature, typically between 0.25°C and 0.5°C.
This spike in your basal body temperature will occur whether the egg has been fertilised or not.
How can it help to know your ovulation temperature?
One of the most useful advantages of keeping accurate records of your ovulation temperature when you are trying to fall pregnant, is the ability to put pinpoint the day when ovulation (and therefore conception) may have occurred.
Most pregnancy tests will not be very accurate until 10 to 14 days after ovulation, so knowing when ovulation occurred will also make sure that you are not using pregnancy tests too early and therefore getting a false negative result.
However, ovulation temperature is not a terribly useful measure to help you fall pregnant in the first month of its use, because you are looking for it to indicate a pattern in your cycle.
The ovulation temperature indicates that you have already ovulated, so you can’t use it to predict ovulation in that same month; it is just a good guide to your normal body rhythm.
By the time you have noted the spike in your basal body temperature that has been caused by ovulation, the egg may well have already left your body.
What is the best way to use the ovulation temperature?
If you create a chart system for yourself that tracks over several months a combination of various ovulation indicators – such as your ovulation temperature, changes in cervical mucus, other ovulation symptoms and even the results of ovulation hormone tests, you will have a very good understanding of your regular pattern.
Don’t forget that hormones are rather sensitive little things which can be affected by all sorts of external forces, like stress, illness, diet and physical activity.
However, it’s true that information is power! By quietly collecting data about the very unique operation of your own body, you can gain greater understanding of its natural rhythms.
If you are planning to fall pregnant, this can be a wonderful way to participate in the next exciting phase of the cycle of life.
For more information see ovulation calculator.
By Fran Molloy, journalist and mum of four