Typical length of a menstrual cycle?

• A. 21 days
• B. 30 days
• C. 40 days
• D. 28 days

Answer: (D)

The length of a menstrual cycle is determined by the timing of ovulation plus the following luteal phase. The luteal phase—the time from ovulation to the start of the next period—is fairly constant, about 14 days. The pre-ovulation “follicular” phase, however, varies from person to person and cycle to cycle, depending on hormonal signals, stress, health, and other factors. When you add a variable follicular phase to a roughly constant luteal phase, many cycles fall near four weeks, or about 28 days. That’s why 28 days is the classic expectation for a typical cycle, even though normal cycles can range from roughly 21 to 35 days. A 21-day cycle is shorter than average and may reflect a shorter follicular phase; a 30-day cycle is within the normal range but less specifically typical; a 40-day cycle is longer than normal and can indicate irregular ovulation or hormonal issues.