Figure 1. Variation in urinary sex hormone levels across the menstrual cycle.

Average estrogen (E1G) and progestogen (PdG) values in the period of ten days preceding ovulation to ten days after the estimated day of ovulation. Values were compiled using data from 12 women for which we had complete hormone and acoustic data for the entire period, as well as from two women for which the first 2 days were missing.