NEW YORK (Reuters Health) - A shorter-than-normal time between menstrual periods may be the first sign of menopause for many women, while heavy bleeding may have other causes, a new study shows.
Researchers found that among women between the ages of 42 and 52, those in the early stage of menopause commonly had shortened intervals between periods -- fewer than 21 days.
Often, these periods were "anovulatory," meaning the women had bleeding but did not ovulate.
In contrast, longer intervals between periods -- more than 36 days -- were more common later in menopause, the study found, the researchers report in the journal Obstetrics & Gynecology.
On the other hand, heavy bleeding appeared to be unrelated to ovulation, according to the investigators, led by Dr. Bradley J. Van Voorhis, of the University of Iowa College of Medicine in Iowa City.
Instead, heavy bleeding was more often seen in women who were obese or had uterine fibroids -- non-cancerous growths that can cause pain as well as heavy menstrual bleeding.
The findings are based on 804 U.S. women who were followed for three years. During that time, they periodically gave urine samples so the researchers could determine whether they were ovulating; they also recorded their monthly menstrual patterns on calendars.
At the outset, the women were separated into groups based on their current menstrual patterns. Those who'd had unpredictable periods for the past three months were considered to be in the early phases of menopause; those who'd skipped two periods or more were considered to be in the late phases.
In general, the researchers found, short intervals between periods were common among women in early menopause, and 44 percent of their periods were anovulatory. Longer intervals were more common in late menopause, and two-thirds of those periods were anovulatory.
Women who had short or long periods -- fewer than four days and more than seven days of bleeding, respectively -- also commonly had anovulatory cycles.
In contrast, the study found, women with heavy periods had relatively few ovulation-free cycles -- suggesting heavy bleeding is not typically related to hormonal changes.
The findings, according to the researchers, suggest that if a woman in early menopause starts to have abnormal timing in her periods -- short or long intervals, or a short or long duration of bleeding -- anovulation should be suspected as the cause.
"In contrast," they write, "if the complaint is only heavy bleeding, anovulation is less likely and careful evaluation for structural lesions including polyps and fibroids is warranted."
SOURCE: Obstetrics & Gynecology, July 2008.