Menstrual Disorders - Introduction

(Page 4)

Length of Monthly Cycle. The menstrual cycle can be very irregular during the first 1 - 2 years, ranging from 21 - 45 days. The length then generally stabilizes to an average of 28 days, although the cycle length may range from 21 - 35 days and still be considered normal. The cycle lengthens when a woman is in her 40s, reaching an average of 31 days by age 49. A number of factors can affect cycle length at any age.

---

---

Length of Periods. Periods average 6.6 days in adolescent girls. By the age of 21, menstrual bleeding averages 6 days until women approach menopause. However, about 5% of healthy women menstruate fewer than 4 days and 5% menstruate more than 8 days.

Normal Absence of Menstruation. Normal absence of periods can occur in any woman under the following circumstances:

• Menstruation stops during pregnancy. Some women continue to have irregular bleeding during the first trimester. This bleeding may indicate a threatened miscarriage and requires immediate attention by the doctor.
• When women breast-feed they are unlikely to ovulate. After that time, menstruation usually resumes, and they are fertile again.
• Perimenopause starts when the intervals between periods begin to lengthen, and it ends with menopause itself (the complete cessation of menstruation). Menopause usually occurs at about age 51, although smokers often go through menopause earlier.

Review Date: 07/26/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).