New research reveals that the durations of menstrual cycles, follicular phases (the period before egg release), and luteal phases (the time after ovulation) can all differ significantly. Notably, the luteal phase shows greater variability than previously thought.
Traditionally, it is believed that every menstrual cycle in which ovulation occurs will have a luteal phase lasting around 14 days. This aligns with the classic understanding of a 28-day menstrual cycle, where ovulation occupies about half of that timeframe. This also supports the statement “All regular menstrual cycles spaced a month apart are ovulatory.”
“We found a broad range of luteal phase lengths in our study, even among healthy premenopausal women who needed to have two consecutive normal-length ovulatory cycles to participate,” explained Sarah Henry, BSc (Hons), MD, the lead author of the study, now completing her family practice residency at the University of British Columbia. She conducted this research during her medical studies. “While the luteal phase length was unpredictable, it was generally more stable than the follicular phase.”
The research, published in Human Reproduction, illustrates that luteal phase lengths can vary considerably. This was measured using the validated Quantitative Basal Temperature© (QBT©) method. According to QBT©, a normal luteal phase lasts 10 days or longer, while short luteal phases are defined as being less than 10 days.
“This year-long investigation is unique as it focuses on within-woman variabilities in follicular and luteal lengths,” said Sonia Shirin MD, MHSc, a CeMCOR research associate and co-author who collaborated with Dr. Henry on data analysis. “We monitored the menstrual cycles of 53 healthy women over the course of approximately a year; most women had at least eight cycles, with an average of 13.”
“What’s surprising is that, after thorough screening, only 6 out of the 53 women (about 11%) maintained normally ovulatory cycles throughout the year,” noted Azita Goshtasebi, MD, MPH, PhD, a co-author and family physician specializing in women’s reproductive health. “Over half (55%) of the women experienced multiple short luteal phases during ovulatory cycles throughout the study period.”
Is a short luteal phase a concern?
Absolutely. A meta-analysis published by CeMCOR in 2014 (Li D, Epidemiol Rev) indicated that women with short luteal phases—both in ovulatory and anovulatory cycles—experienced bone loss when compared to those with more typical ovulatory cycles over a year, even if their cycles were consistently one month apart. Additionally, short luteal phases and cycles lacking ovulation may be linked to difficulties in conceiving.
“I wish I had realized that my regular, month-apart menstrual cycles might be hiding silent ovulatory irregularities that could impact my fertility,” expressed Sophia Park, MD, FRCPC, MBA, an associate clinical professor in Pathology and Laboratory Medicine at the University of British Columbia, who has firsthand experience with infertility.
“Understanding our own ovulation and luteal phase lengths is crucial. Why is that? Because growing evidence suggests that while estrogen, a strong growth stimulant, is important, it must be balanced by progesterone, which decreases proliferation and promotes cell development and specialization,” stated Jerilynn C. Prior, BA, MD, FRCPC, the senior author and a professor of endocrinology at the University of British Columbia.
The researchers emphasize that this new understanding of luteal phase variability is significant for two main reasons:
- We cannot assume that menstrual cycles spaced a month apart indicate ovulation or normal-length luteal phases.
- Women should be informed about their ovulation for both health and fertility reasons.
