If a woman has a very regular cycle, it is likely that she will ovulate halfway through her cycle. If she wants to be more certain, the most common method of finding out whether, and if so, when ovulation occurs, is to take the basal body temperature daily and enter it on a chart. It is a good idea to keep this information for a couple of months to determine whether there is a pattern in the cycle. Besides checking whether there is a temperature increase halfway through (which can be an indicator of ovulation), charting your cycle also shows how long the cycle is each month.

Some women can better predict their ovulation in this way and better time intercourse for the most optimal days in the month. In addition, a possible change in the discharge may be noted. Charting is a simple routine that must be carried out every morning.

The basal body temperature, or BBT, is the normal temperature of a healthy person immediately after waking in the morning. A woman’s BBT varies from 36.11ºC to approximately 36.38ºC around ovulation as the hormonal changes associated with ovulation cause an increase of between 0.18ºC and 0.60ºC, which lasts at least until the start of the next menstrual period. The temperature may still show peaks on other days, but unless it remains at a high level, the woman is unlikely to be ovulating. Women are at their most fertile on the day of the peak and for a couple of days before it.

The BBT must be measured using a basal thermometer. This thermometer is extremely sensitive and more accurate than a standard thermometer. Digital models are best. Here are a few essential guidelines for women monitoring their BBT.

Immediately after waking each morning, women must take their BBT and make a note of it. Most basal thermometers come with a chart allowing you to keep an accurate record of the temperature. Keep all your charts so that you can discuss them later with a doctor if appropriate. Three or four months of consistent charting should be enough to discern patterns and trends in a woman’s cycle.

The basal body temperature must always be recorded:

• Every day at the same time - after waking up in the morning and before doing anything else such as taking a shower.
• In the same place - the mouth, vagina or rectum.

Some advantages of charting:

• A cheap way to improve the chance of pregnancy.
• Accurate - if kept correctly and consistently.
• A personal way of gaining an insight into your cycles.
• An information aid that can be particularly useful if you have irregular cycles.

A few disadvantages of charting:

• A hindrance to daily habits.
• It can take up to three months for patterns to become apparent.
• Can increase preoccupation with your desire to have a child adding to stress.

Taken as a whole, the advantages of charting outweigh the disadvantages. Having these temperature charts is useful for home use in the short term, but also for the long term in case a doctor has to be consulted.