Figure 2.

Plot of day-specific serum E2 levels, indexed to Day 0, day of serum luteinizing hormone (LH) peak, from three assays: Dighe et al. [18], Roos et al. [19], and Stricker et al. [20]. The dotted vertical line is at Day −4; the horizontal solid red line is at the lower limits (lower 99% CI, 10th percentile (PCTL), 5th PCTL) of the E2 levels. Top: The day-specific mean and 99% confidence interval (CI) limits for E2 are shown for Dighe et al. The lower 99% CI limit was 411 pmol/L (112 pg/mL) at Day −4. The interval, Day −4 to Day +1, is taken as the period of potential fertility [5,6,7]. The fertile start day (FSD), the day to start abstinence to avoid pregnancy with a fertility awareness method (FAM) of family planning, is determined by the lower limit of E2 at Day −4. To include the upper as well as the lower 99% limits of the cohort (red region), abstinence should begin on ~Day −6. Middle: The day-specific median and 10–90th PCTLs for E2 are shown for Roos et al. The 10th PCTL limit was 263 pmol/L (71.6 pg/mL) at Day −4. In this case, to include the 90th PCTL as well as the 10th PCTL, abstinence should begin on ~Day −9 to avoid pregnancy. Bottom: The day-specific mean and 5–95th PCTLs for E2 are shown for Stricker et al. The 5th PCTL was 186 pmol/L (50.6 pg/mL) at Day −4. In this case, to include the 95th PCTL as well as the 5th PCTL, abstinence should begin ~Day −14 to avoid pregnancy. The Dighe et al., high-resolution E2 reference ranges had the least variance and therefore the least restrictive FSD for abstinence with a potential FAM of family planning.