Q: What is a biphasic curve?

A: The basal body temperature rises and stays up after ovulation because of the progesterone hormone being produced by the corpus luteum after ovulation. This hormone increases BBT. A typical biphasic curve has two distinct phases:

• The first phase of lower temperatures before ovulation (follicular phase), and
• The second phase of sustained higher temperatures (at least 0.2 degrees) after ovulation (corpus luteum phase).

A biphasic (two-phase) curve is a typical ovulation curve when the temperatures rise around mid-cycle and stay up until the next menstrual period. Ovulation has to be established first in order to determine that the curve is biphasic, and temperatures have to stay elevated for at least three or more days for ovulation to be determined with some certainty. The typical biphasic temperature pattern can be established 3-4 days after typical ovulation, but it is optimally established at the end of the menstrual cycle when the complete curve can be evaluated.