A biphasic curve has two phases: It is a curve that rises and stays up after ovulation. The first phase is before ovulation (follicular phase), the second phase is after ovulation (corpus-luteum phase), when temperatures rise because of progesterone. A triphasic curve has three distinct phases:
- The first phase of lower temperatures before ovulation (follicular phase),
- The second phase of higher temperatures after ovulation (corpus luteum phase). At ovulation the basal body temperature rises and stays up because of the progesterone hormone, which is being produced by the corpus luteum and increases the BBT, and
- The third phase, where the BBT curve again rises to a third level (triphasic) of temperatures about a week or so after ovulation.
The triphasic curve supposedly shows implantation, but there is no sufficient scientific evidence to prove or disprove this. Many typical pregnancy curves are not triphasic, and many women who have triphasic curves turn out not to be pregnant.