Fig. 15. Calculating integrated progesterone. Blood samples were drawn daily over the luteal phase in menstrual cycles from two different women. Both luteal phases were 14 days long. The blood samples were assayed for progesterone, then graphed over the luteal phase. The area under the progesterone curve was calculated as an integrated progesterone. The integrated progesterone values were 168.5 ng/day/mL (normal) for the woman in A and 74.7 ng/day/mL (abnormal; luteal phase deficiency) for the woman in B.