All participants will have a small blood sample (2 teaspoons) drawn once a day on days 10, 14, 17, 19 and 21 of their menstrual cycle and three times a day on day 6 and for a period of 8 days, starting 5 days before the expected menses and continuing for 3 days of the next cycle. For the days with three blood draws, a small needle that can stay in place for up to 72 hours will be placed in the arm to avoid the discomfort of multiple needle sticks.