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Ovulation and menstrual cycles

Overview

It was commonly believed that we always ovulated whenever we were having regular menstrual flow with normal-length menstrual cycles of 21-35 days apart. CeMCOR and other groups of scientists have now shown that variability in ovulation and huge variation in the amount of progesterone that each menstrual cycle makes are very common. This frequent but not obvious cycle variation is called an "ovulatory disturbance" that includes not releasing an egg (anovulation) as well as releasing an egg with too short a time from egg-release to the next flow (short luteal phase). Ovulatory disturbances are silent within regular and normal menstrual cycles. It is still true, however, that irregular or far apart cycles are even more likely to have ovulatory disturbances.

Who's at increased risk for silent, ovulatory disturbances? We don't know for sure because few studies have tracked women's cycles for ovulation over extended periods. Adolescent and young women (in the first 10 years after first period or menarche) are more likely to have ovulatory disturbances; irregular flow is also common in the first year. Also, women in perimenopause have increasing ovulatory disturbances; luteal lengths can be normal but progesterone production too low during this life phase. Obesity is associated with ovulatory disturbances, as is cigarette smoking. But probably the most common reason for having a regular cycle with too little or no progesterone production is being under stress: the "threat" can be physical (illness, over-exercise), emotional (break-up with a partner, grief, depression), nutritional (not being able to afford or get to, enough nutritious food or not eating enough for body needs), social (bullying, sexual abuse, social isolation) or spiritual (not feeling life has fundamental meaning). Thus CeMCOR investigators have come to see a normally ovulatory, regular menstrual cycle as a sign of health and well-being.

Do ovulatory disturbances matter? Yes. We all know that normal ovulation is needed for fertility. But CeMCOR scientists recently showed that half of about 430 women had over a third of cycles with ovulatory disturbances per year in a review of all published scientific articles about changes in ovulation and in spinal bone in young women. Thus women with less than a third of cycles having ovulatory disturbances each year kept their peak bone mass but the rest, with more frequent ovulatory disturbances, were losing almost one percent of spinal bone density a year. So for premenopausal women's bone health, normal ovulation as well as menstruation matters. Normal premenopausal ovulatory menstrual cycles likely also matters for the later risk of heart disease and breast cancer.

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Enrolment complete: Perimenopausal Hot Flush Study

Enrolment is now complete. Thank you for your interest.
CeMCOR is now recruiting Canadian women for this CIHR-funded randomized controlled trial to test whether oral micronized progesterone is more effective than placebo as therapy for hot flushes and night sweats in perimenopausal women.

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