The periodicity of menstrual cycle averages ... days.

Appeared in: MNS 2015

Explanation

The universally accepted average length of a menstrual cycle is 28 days, which serves as a standard benchmark in clinical practice.
While the average is 28 days, a normal cycle in adults can range from 21 to 35 days.
This 28-day model is a standard baseline for clinical calculations and for teaching the different phases of the cycle.
Variations in the total cycle length are most often due to changes in the duration of the follicular phase, as the luteal phase is relatively constant at about 14 days.

Why Other Options Were Wrong

Option A: A 27-day cycle is within the normal physiological range (21-35 days) but is not the established average.
Option C: A 29-day cycle is within the normal physiological range (21-35 days) but is not the established average.
Option D: A 30-day cycle is within the normal physiological range (21-35 days) but is not the established average.

Related Visual

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Average length of the menstrual cycle as background academic context rather than a clinical decision trigger.
Understanding the 28-day average is fundamental for nurses in obstetrics and gynecology, especially for calculating the estimated date of delivery (EDD) using Naegele's rule.
Nurses educate patients that while 28 days is the average, variations are normal. However, consistently irregular, very short (less than 21 days), or very long (greater than 35 days) cycles may warrant a medical evaluation.
What if? If a patient consistently has a 40-day cycle, it falls outside the normal 21-35 day range. This could indicate an underlying issue like Polycystic Ovary Syndrome (PCOS) or thyroid dysfunction, and the nurse should advise the patient to consult a healthcare provider.

How to Approach the Question

Identify the core of the question: it asks for the 'average' periodicity of the menstrual cycle.
Recall foundational knowledge from reproductive physiology.
Recognize that while individual cycles vary, there is a standard 'textbook' average used for clinical reference and calculations.
Evaluate the options. 28 is the standard average. The other numbers (27, 29, 30) are close and represent normal variations but are not the average.
Select the option that represents the standard clinical average.

Concept Tested & Keywords

Concept Tested: Average length of the menstrual cycle
Stem keywords: periodicity, menstrual cycle, averages
Lead-in keywords: averages

Question ID

QdcHKg94e-kf8Y9SFYCzm_

Reference Book

E6 Gynecology Williams p. 365-431

E6 Medicine Harrison 22e Part 2 p. 1034-1036

E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) p. 8369-8371

Practise the full MNS 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.

Attempt this paper Attempt in the NPrep app