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The important details about the menstrual cycle and what it means to be irregular

When trying to figure out what’s “normal,” twenty-eight days is the magic number that you may have heard before – but this describes the length of the average cycle, and it’s the number that most estimates use as a baseline for figuring out when menstruation and ovulation will happen. And there’s a difference between an average cycle and a regular one – for some people, a 23-day cycle can be as regular as clockwork every month.

What having a “regular” menstrual cycle really looks like

It helps to know what, technically, qualifies as an irregular cycle to understand what “regular” really means. The definition of an irregular cycle is one that lasts less than 21 days or more than 35 days, and has more than 7 days of variation between its shortest and longest lengths. However, even menstrual cycles that are, technically, regular can be unpredictable. And on the other hand, for someone with irregular cycles, that exact 28-day cycle may come up once or twice every three to nine months.

Variations in different phases of the menstrual cycle

In either case, when there’s a variation in the menstrual cycle, it’s worth noting that it most commonly happens in the proliferative phase. A quick refresher: The menstrual cycle follows a series of phases, from menstruation, to the proliferative phase when the new egg follicles develop, to ovulation when that egg is mature and ready to be fertilized, to the luteal phase when an unfertilized egg is broken down, and all the way back to menstruation, when the broken-down components of the unfertilized egg are released as menstrual blood. The proliferative phase is the one which most commonly causes changes and irregularities in the menstrual cycle because it is the phase that is most influenced by outside factors.

In a cycle that is a different-from-average length – whether that means shorter, at 24 or 25 days, or longer, at 29, 30, or even up to 6 weeks – the proliferative phase may be a different length from the average for reasons that remain steady, like an individual’s personal hormonal makeup, or environmental or lifestyle factors. The proliferative phase, and the menstrual cycle in general, can be influenced by any number of factors – from stress to physical activity to diet.

This is also true of the proliferative phase in women with irregular cycles. Irregular cycles are common –  in fact, in one study, more than 40% of females saw a variation from cycle to cycle of 7 days or more. And many of the factors that can impact the proliferative phase, and the menstrual cycle in general, can vary from day to day, month to month, and year to year. Irregular cycles are also more common in those whose periods have just begun or in those who are approaching menopause.

On the other hand, the luteal phase, which happens after ovulation, is much more stable. The factor which influences the luteal phase the most is whether the egg is successfully fertilized. If the egg isn’t fertilized, the luteal phase leads to menstruation on a much more regular timeline.

Figuring out what’s normal for you

So when it comes to what’s regular, really, there’s a range. And what’s normal for you may be totally different from what’s normal for other people – what’s normal for some people may even, technically, be irregular! There’s obviously a lot of variation, and tracking your cycle with Ovia can help you figure out what’s going on with your own unique cycle.

  • Kathryn Clancy. “I don’t have a 28-day menstrual cycle and neither should you.” Scientific American. Scientific American, a division of Nature America Inc. 23 December 2010. Retrieved March 21 2018. https://blogs.scientificamerican.com/guest-blog/i-dont-have-a-28-day-menstrual-cycle-and-neither-should-you/.
  • Richard Fehring, Mary Schneider, Kathleen Raviele. “Variability in the phases of the menstrual cycle.” Journal of Obstetric, Gynecologic, & Neonatal Nursing. 35(3): 376-384. May/June 2006. Retrieved March 21 2018. https://pdfs.semanticscholar.org/f0c4/af7e04d1fd2c1926a18468410c1865d92046.pdf.
  • Yan Liu, et al. “Factors affecting menstrual cycle characteristics.” American Journal of Epidemiology. 160(2): 131-140. July 2004. Retrieved March 21 2018. https://academic.oup.com/aje/article/160/2/131/76508.
  • Anne Marie J. Zukic, et al. “Life-style and reproductive factors associated with follicular phase length.” Journal of Women’s Health. 16(9): 1340-1347. March 2010. Retrieved March 21 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2834565/.

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