Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles

What this work gives Aellic

612,613 cycles with ovulation confirmed by basal temperature and LH: cycle length 29.3 ± 5.2 d, follicular phase 16.9 ± 5.3 d, luteal phase 12.4 ± 2.4 d. Variance ratio follicular:luteal ≈ 4.9:1 — all of the spread sits BEFORE ovulation. This is why ovulation is estimated backwards from the next expected period: going backwards inherits the luteal SD of 2.4 instead of the follicular one of 5.3. It also carries `DEFAULT_CYCLE_LENGTH = 29` (only 13 % of all cycles really run 28 days; the mean is 29.3).

Where this sits in the engine

4 declared sites — constants and thresholds in the code that point at this entry.

• Cycle Phases and cycle-aware baselines 4 sites