How to read your basal body temperature chart
A lower temperature phase and a higher temperature phase
The interval from the first day of your period to the day your next period begins constitutes a cycle. Try charting your basal body temperature for one cycle as a starting point. You can then see how your basal body temperature changes during a cycle.
For example, a woman with a 28-day menstrual cycle will have lower temperatures for the two weeks following the first day of her period. Her temperature rises once ovulation occurs, followed by roughly two weeks in a higher temperature phase. As her temperature drops again, her next period begins. A healthy woman’s basal body temperature will show two such distinctive phases, one of lower temperatures and one of higher temperatures.
The changes in body temperature during the menstrual cycle are caused by female hormones. You will have lower basal body temperatures between menstruation and ovulation, during which progesterone levels are low. Once ovulation occurs, your basal body temperature rises along with the rise of progesterone levels, which have the effect of raising the body’s temperature.
Having a biphasic basal body temperature is evidence that you ovulate and have normal levels of female hormones.
Various patterns of basal body temperature to be aware of
A normal pattern of basal body temperature
Ovulation occurs after about two weeks of a lower temperature phase, followed by about two weeks of a higher temperature phase. The menstrual period starts once the higher temperature phase ends.
A basal body temperature pattern indicating pregnancy
You are likely to be pregnant if the higher temperature phase continues for more than three weeks after ovulating, as this indicates continued secretion of progesterone.
A basal body temperature pattern indicating an anovulatory cycle
If your basal body temperature continues to remain low it may indicate the lack of ovulation.
Another basal body temperature pattern indicating an anovulatory cycle
If you have low levels of progesterone, the higher temperature phase, that normally lasts for about two weeks, may last fewer than 9 days. This could also cause infertility.
What you can tell from your basal body temperature
Identifying your day of ovulation or your next menstrual period
You can identify your ovulation day by charting your basal body temperature. You are most fertile on the day of ovulation or the following day. If you want a baby, you are more likely to become pregnant if you have sexual intercourse on those days.
Women with regular menstrual cycles will be able tell whether they are pregnant by reading their basal body temperature chart. Typically, a higher temperature phase lasts for about two weeks before your period starts. There is a high likelihood of pregnancy if your period is late, and you have a higher basal body temperature for more than three weeks.
You can also identify your ovulatory phase using the basal body temperature chart in order to avoid pregnancy, but this alone is not a sufficiently reliable form of contraception. In order to avoid pregnancy, it is more appropriate to use contraceptive devices or contraceptive pills.
The chart will also be useful in making plans such as when traveling, by helping you predict your next menstrual period.
Detecting hormone imbalances
To some extent, hormonal imbalances can also be detected by charting your basal body temperature. If you have a persistent lower temperature phase with no signs of ovulation, it shows that you have anovulatory cycles despite still having periods most months. You can also detect a luteal phase defect that causes infertility from noting a shorter phase of high temperatures.
If you are being treated for infertility, you are always asked to chart your basal body temperature. However, a basal body temperature chart is not only quite useful for infertility treatment but also for any other consultation or treatment with a gynecologist.