Updated April 28, 2014.
The so-called menopausal transition in a woman refers to the years leading up to full menopause, when menstruation ceases altogether. This transition is also commonly called perimenopause.
The menopausal transition can last anywhere from 2-10 years, during which time many women have very unpredictable and variable periods, along with other symptoms such as hot flashes, mood swings and sleep disturbances.
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According to a longitudinal study published in the BJOG: An International Journal of Obstetrics and Gynaecology, a woman's periods can be much heavier or prolonged compared with those in earlier years, during this time. In fact, 91% of the 1320 older women studied for more than a decade had at least one period lasting 10 days or more. Three-quarters of the subjects had at least three of these lengthy periods as they approached full menopause.
As lead author and epidemiology professor at the University of Michigan's School of Public Health Siobhan Harlow tells me, menstrual cycles can change quite dramatically over the course of a woman's reproductive life.
"Patterns change from girlhood to adulthood, with periods becoming most predictable for women in their 30s," she explains. Then they tend to change most dramatically in the 5-8 years as you approach the menopausal transition; shifting from periods you can predict quite easily to those which are perhaps prolonged and heavy, and very different from what you're accustomed to."
Periods can also stop for months and then start again during the menopausal transition. You can still get pregnant until you have gone completely through menopause, without a period for one full year.
Sources:
Menopause. US National Institute on Aging Public Information Sheet. Accessed April 25, 2014.
http://www.nia.nih.gov/health/publication/menopause
Paramsothy P, Harlow SD, Greendale GA, Gold EB, Crawford SL, Elliott MR, Lisabeth LD, and Randolph JF Jr. "Bleeding Patterns During the Menopausal Transition in the Multi-Ethnic Study of Women’s Health Across the Nation (SWAN): a Prospective Cohort Study." BJOG Article first published online: April 16, 2014. doi: 10.1111/1471-0528.12768.
Sioban Harlow, Professor of Epidemiology and Director, Center for Integrated Approaches to Complex Diseases (CIACD). University of Michigan School of Public Health. Interview conducted by phone April 17, 2014.