March 18, 2005 -- Subtle changes in menstrual cycle length are among the first signs that a woman in her late reproductive years has begun the transition to menopause, a newly reported study shows.
Researchers found that even slight changes in bleeding patterns were often associated with major changes in fertility-related hormone levels. The observation could help women and their physicians identify the transition to menopause earlier than ever, they say.
"I think it is fair to say that this very early stage of transition has not gotten much attention and has been difficult to characterize," says study co-author Ellen W. Freeman, PhD, of the School of Medicine at the University of Pennsylvania.
"This study suggests that these hormonal changes can be detected and measured earlier than has generally been assumed. And changes in cycle length can predict these hormonal changes."
Age Is Poor Predictor
A woman is said to have reached menopause when she has not had a period for a year. The average age when this occurs is 51. But because some women reach menopause in their early 40s and others in their late 50s, age is a poor predictor of menopausal status.
The period of transition to menopause, when women often experience hot flashes and other hormonally driven symptoms, is widely accepted to last around four years. But the new study shows that hormonal changes may often occur much earlier than this, Freeman says.
"This is important for women to know if they are having hot flashes or other symptoms," she tells WebMD. "Physicians may not associate these symptoms with the transition to menopause in younger women."
The study involved 427 women between the ages of 35 and 47 who were followed for five years. Researchers checked fertility-related hormone levels periodically, and the women also provided detailed information about the timing of their monthly cycles.
Writing in the March/April issue of the journal Menopause, researcher Clarisa Gracia, MD, and colleagues found that even small changes in cycle length were associated with changes in two important fertility hormones -- FSH and inhibin B.
While many women experience shorter-than-normal menstrual cycle length early in the transition to menopause, others have cycle lengths that are longer than they normally would be, Freeman says. Cycle length is from the first day of your period to the first day of your period in the next cycle.
As the transition progresses, cycle length tends to get longer and periods are missed.
Some women have heavier periods early in the transition to menopause and others have lighter-than-normal flows.
"Because the transition is gradual over years and does not depend on age alone, it is important to be aware of early bleeding changes to identify women beginning this phase of their lives," Gracia and colleagues wrote.
Renown menopause expert Isaac Schiff, MD, noted that the researchers found large variations in hormone levels among the women in the study, suggesting that hormonal status alone is a poor predictor of menopause status. Schiff is chief of obstetrics and gynecology at Massachusetts General Hospital, and a professor of gynecology at Harvard Medical School in Boston.
"This study verifies that menstrual cycle changes can be used to determine a woman's menopause transition stage," he noted.