The length of perimenopausal menstrual cycles increases later and to a greater degree than previously reported.
OBJECTIVE
To demonstrate that the perimenopausal increase in menstrual cycle length presented by Treloar et al. was biased by misidentified menopause dates, mean values classified by calendar year, and exclusion of menstrual cycles straddling two calendar years; and to use the revised data to investigate women's experiences of longer perimenopausal cycles.


METHODS
Secondary analysis of prospectively collected menstrual cycle data.


METHODS
Center for Population and Health, Georgetown University.


METHODS
One hundred twenty white, college-educated, US women in the Tremin Research Program on Women's Health.


METHODS
None.


METHODS
Mean cycle length and time spent in >40-day cycles, by year before menopause.


RESULTS
Mean estimates for each of the 4 years before menopause were 30.48, 35.02, 45.15, and 80.22 days, respectively, compared with the original analysis: 33.60, 43.91, 55.87, and 54.58 days. In the year before menopause, the majority of women spent >or=75% of their time in cycles >40 days long.


CONCLUSIONS
Treloar's estimates of mean cycle length were biased. Long cycles occurred throughout perimenopause, but the largest increase in mean cycle length did not occur until the final year before menopause. New estimates of the time spent in cycles >40 days may be useful clinically as well as epidemiologically for assessing menopausal onset and symptomatology.
Ferrell
Rebecca J
RJ
Center for Population and Health, Georgetown University, Washington, DC 20057-1197, USA. rebeccajferrell@gmail.com
Simon
James A
JA
Pincus
Steven M
SM
Rodríguez
Germán
G
O'Connor
Kathleen A
KA
Holman
Darryl J
DJ
Weinstein
Maxine
M
D000328:Adult; D017677:Age Distribution; D002986:Clinical Trials as Topic; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008597:Menstrual Cycle; D008875:Middle Aged; D047648:Perimenopause; D010507:Periodicity; D012189:Retrospective Studies; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D016387:Women's Health