Peak Day
Peak Day is the last day in a menstrual cycle on which cervical mucus is clear, stretchy (like raw egg white), or lubricative, and is used as a primary ovulation reference point in mucus-based fertility awareness methods, including the Creighton Model FertilityCare System.1 Peak Day correlates closely with follicular rupture, occurring within plus or minus two days of ovulation in approximately 95% of cycles.1 Crucially, Peak Day is identified retrospectively: a woman recognizes it the day after it occurs, when fertile-type mucus has ceased. The day after Peak Day is called post-peak day 1 (P+1). In NaProTECHNOLOGY, Peak Day is the reference anchor for cycle-timed diagnostic blood draws, particularly the post-peak day 7 (P+7) progesterone and estradiol measurements used to evaluate luteal phase adequacy. Accurate Peak Day identification is foundational to NaPro hormonal support protocols and to the diagnostic value of the entire charting system.
Cited in this entry
- Pregnancies, intentions, and fertility behaviors during use of the Creighton Model FertilityCare System. https://pmc.ncbi.nlm.nih.gov/articles/PMC12306780/
Discussed in
Research library
- Comparison of woman-picked, expert-picked, and computer-picked Peak Day of cervical mucus with blinded urine luteinising hormone surge for concurrent identification of ovulation
- Accuracy of the peak day of cervical mucus as a biological marker of fertility
- The Identification of Postovulation Infertility with the Measurement of Early Luteal Phase (Peak Day +3) Progesterone Production
- Pilot test and validation of the peak day method of prospective determination of ovulation against a handheld urine hormone monitor
- Chapter 27: Cooperative Progesterone and Estrogen Replacement
Patient questions
This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.