Laparscopic view of an ovary showing the ovulation point in the ovary

Progesterone levels are less than 1 ng/ml early in the menstrual cycle, and reach their peak midway between ovulation and the onset of the next menses (midluteallevel).  After ovulation progesterone is produced in the ovary from the organ that develops where the egg was formed called the corpus luteum.  This organ maintains the early pregnancy until the develping placenta takes over production of progesterone at about 73 days from last menstral period.  A woman is considered to have ovulated if the midluteal progesterone is above 3 ng/ml, but levels usually around 10-20 ng/ml are detected.

Progesterone falls from its midluteal high just prior to the onset of the next menses.  In fact, rising progesterone prior to the expected menses can frequently be the first suggestion of an early pregnancy.