Tamara Thomas

Urban Health Today

A new study published in Human Reproduction revealed that the menstrual cycle luteal phase is not &#8220;fixed&#8221; at 13-14 days as previously believed but is highly variable. 
The duration of the luteal phase, the interval between ovulation and the onset of menstruation, is commonly thought to be approximately 14 days. This phase is believed to constitute half of a typical menstrual cycle during ovulation. 
Researchers at the University of British Columbia, led by Dr. Sarah Henry, investigated the variation in luteal phase length relative to the follicular phase in women with typical menstrual cycles.
The researchers analyzed the data of 53 women with complete data for 8 or more cycles. The women in the study were between the ages of  21 and 41, had normal body mass index, and had normal cycle lengths (21-36 days). Overall, Dr. Henry and the team analyzed about 694 cycles.
The findings reveal that the one-year averages for the menstrual cycle, follicular phase, and luteal phase durations were 10.3, 11.2, and 4.3 days, respectively. Furthermore, the researchers found that the median variability for cycle length, follicular phase, and luteal phase within an individual woman was 3.1, 5.2, and 3.0 days, respectively.
Researchers observed that over half of women with regular cycles (55%) will have at least one short luteal phase, defined as less than 10 days, despite 98% of these women having regular cycle lengths overall. They also found that 17% experienced an anovulatory cycle (when the ovaries don’t release an egg).
&#8220;An amazing thing is that, despite rigorous screening, only 6 of 53 women (11%) had normal ovulatory cycles the whole year,&#8221; said Dr. Azta Goshtaseb, co-author and family physician. &#8220;Fifty-five percent of women across the study year had more than one short luteal phase in an ovulatory cycle.&#8221;      
The researchers also observed that the differences in follicular phase length within the same woman were significantly greater than in luteal phase length. However, they found that women who experienced any anovulatory cycles (n = 8) had significantly greater variability in the length of their follicular and luteal phases than women with completely normal ovulatory cycles (n = 6).
Dr. Henry added, &#8220;Although the luteal phase was not predictable in length, it was usually less variable than the follicular phase.&#8221;
According to senior author Dr. Jerilynn Prior, &#8220;It is important to know about our own ovulation and luteal phase lengths. Because increasing evidence says that estrogen, a powerful growth stimulator, needs to be counterbalanced. Progesterone decreases proliferation while encouraging cells to become more well-developed and specialized.&#8221; 
Dr. Henry and the team concluded that it is important not to assume month-apart menstrual cycles mean ovulation or normal-length luteal phases.
Source:<a href="https://www.sciencedaily.com/releases/2024/10/241007134019.htm"> Science Daily</a>
Journal:<a href="https://academic.oup.com/humrep/article/39/11/2565/7775370"> Human Reproduction</a>

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Study Finds Variations in Menstrual Cycle Luteal Phase Duration, Even Among Healthy Women

Reproductive Health

A new study revealed that the menstrual cycle luteal phase is not "fixed" at 13-14 days as previously believed, but is highly variable.