Charting of the menstrual cycle is one of the first tools that a woman can use to determine when she's ovulating. In general, as the menstrual cycle progresses, and progesterone is produced at the time of ovulation, a woman's temperature begins to rise. We call that a biphasic curve. In the first 14 days of the cycle, or the first half of the cycle, temperature levels are low. In the second half of the cycle, temperature levels rise. The ability to detect that temperature rise will detect when a woman is, in fact, ovulating. Woman can therefore start testing their temperature, usually the first thing in the morning, or at least at the same time every day, starting on day one of their period.
Some woman are a little bit confused about what is truly day one of their period. Is it the first day of spotting or is it the first day of flow? Well, unfortunately, there is no consensus among fertility doctors about what is truly day one. Most, however, consider the first day of flow as the first day of the menstrual cycle. That's the first day that the temperature should be taken, recorded, and should be taken everyday at the same time. If a woman has a fever at a particular time, has the flu, a cold, any other thing that is going on, she should record that at the time. In addition, she should consider looking at her cervical mucus.
Although, some women are uncomfortable with this, cervical mucus can tell a lot about when ovulation is occurring. Cervical mucus that's very watery and thin tends to occur when estrogen levels are high, and prior to ovulation. Post-ovulation, mucus becomes very, very thick, and viscous. In pregnancy, it becomes so viscous that it forms what is called the mucus plug, that protects the cervix from outside contaminants. Basal body temperature testing is an important component of early management of fertility issues.