ACOG guidelines on menstrual health and cycle norms
ACOG considers the menstrual cycle a critical vital sign of overall female reproductive and endocrine health.
The normal cycle interval in adult women is 24 to 38 days, with bleeding duration between 4.5 and 8 days. Cycles shorter than 24 days or longer than 38 days are classified as abnormal uterine bleeding (AUB).
Documenting period dates, cycle length variance, and bleeding intensity provides essential clinical data for diagnosing ovulatory dysfunction, uterine fibroids, or adenomyosis.
Worked example: US cycle evaluation
With an LMP of August 1st and a 27-day cycle:
Next cycle start dates are August 28th, September 24th, and October 21st.
The cycle parameters fall well within ACOG normal reference ranges.
US period inputs
Cycle Duration
Days between period onset dates.
CALCULATOR QUESTIONS
ACOG menstrual cycle predictor questions
When should I see an OB-GYN about my period?
ACOG recommends seeing a doctor if your period stops for more than 90 days, if cycles occur more frequently than every 21 days, if bleeding lasts longer than 8 days, or if you experience severe pelvic pain.
How does perimenopause affect period predictability?
During perimenopause (typically beginning in the mid-forties), declining ovarian follicle count causes estrogen fluctuations, frequently resulting in cycles that vary by 7 or more days.