(A) Daily endogenous estradiol exposure observed over 28 days in nmol/l based on data from 12 studies of women in the US and Europe (N = 181 women and 302 ovulatory cycles). Solid line and circles are the mean endogenous estradiol exposure with 95% confidence intervals. Dashed line is median exposure. (B) Daily endogenous progesterone exposure observed over 28 days in nmol/l based on data from 12 studies. Solid line and circles are the mean endogenous progesterone exposure with 95% confidence intervals. Dashed line is median exposure