Unprotected Intercourse — The Timing Clock Starts Now
Every EC decision is measured from a single starting point in time.
- 2 main: EC options available (LNG and UPA oral pills)
- Cu-IUD: Backup option (most effective, up to 5 days)
- 0–120h: Decision window (sooner is always better)
- OTC / Rx: Access (varies by drug and region)
Why timing matters
Placeholder: earlier EC use consistently improves outcomes.
Hours Since Intercourse — Racing the Effectiveness Curve
Every EC method loses effectiveness as hours accumulate.
- <24h: Ideal window (highest efficacy for both drugs)
- 72h: LNG label limit (FDA-approved window)
- 120h: UPA label limit (FDA-approved window)
- Declining: Efficacy trend (monotonic with hours elapsed)
Countdown dynamics
Placeholder: the timeline curve shows falling protection hour by hour.
Levonorgestrel — Fast-Acting but Time-Sensitive
LNG delays ovulation but loses power quickly after intercourse.
- Delays LH surge: Mechanism (blocks/delays ovulation)
- ~95%: Peak efficacy (within first 24 hours)
- Reduced: BMI sensitivity (less effective at higher BMI)
- OTC: Availability (no prescription needed, most regions)
LNG decay profile
Placeholder: steep drop-off in protection after about 72 hours.
Ulipristal Acetate — A Longer, Flatter Window of Protection
UPA blocks ovulation closer to the LH peak, extending usefulness.
- Progesterone modulator: Mechanism (blocks LH surge later too)
- ~85–88%: Peak efficacy (sustained across 5 days)
- More robust: BMI sensitivity (than LNG at higher BMI)
- Rx only: Availability (in most regions)
UPA decay profile
Placeholder: efficacy declines gradually, staying useful through day 5.
Menstrual Cycle Phase — Ovulation Timing Shapes Real Risk
Baseline pregnancy risk without EC peaks near ovulation.
- ~6 days: Fertile window (ending at ovulation)
- Day 0: Peak risk day (ovulation day, relative)
- Early/late cycle: Low-risk phase (far from ovulation)
- 28 days: Cycle length used (simplified average model)
Cycle-risk overlay
Placeholder: risk rises and falls with proximity to ovulation.
Placeholder: EC choice should still favor speed over cycle-day precision.