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730 E 38th Street
Minneapolis, MN, 55407

A revolutionary approach to fertility. Through our flagship programs Fertility Pilates™ and Movement For Fertility™ we teach and instruct women about all the ways that aligned exercise & movement naturally foster the process of trying to conceive. We are also proud to offer Merciér Therapy to women seeking to get pregnant.


Is a 28-day cycle really a good sign of women's health?

Marie Wittman

A woman’s health is often defined by two questions: “Is your cycle regular?” meaning does it occur every 28 days; and: “How many days does your period last?” In many doctor visits, there is not any further inquiry. While cycle and menses length can give a basic sense of the health of the female reproductive system, they do not always provide the most accurate picture of your health.

First of all, there is a possibility that you may be unknowingly providing your medical practitioner with imprecise information. A study has shown that many women report their cycles to be regular (happening every 28 days), when in fact their cycles vary appreciably. In the study, of the women who told the researchers that their cycles adhered to the 28-day model:

  • 50% had cycles that actually ranged 6 days in length
  • 25% had cycles that actually ranged greater than 2 weeks in length

If a practitioner does not explore the topic with you any further, she/he may be missing important insights into your overall health.

On the other hand, some women know their cycles do not fall within that 28-day model and sharing with the doctor that they have a 25-day cycle or a 32-day cycle, for example, may trigger a host of tests or interventions to control the body in an effort to get back to the ideal of 28 days, however, cross-cultural studies show that there is substantial variation in cycle length temporally (from one cycle to the next in one woman), among women, and among populations. From an evolutionary perspective variation (25 days one cycle and 33 the next, for example) is more natural than the ideal of a regular pattern (28 days like “clockwork”).[1]

In fact, the notion that a healthy woman should have a 28-day ovulatory menstrual cycle rests more upon Thomas Malthus’s “Essay on the Principle of Population” (1798) than biological reality. His view that reproduction would act with machine-like regularity persists today even though scientists have been challenging the Malthusian model since the 1980s.

That said a consistently shorter or longer cycle could be an indication of a health issue. For example, a shorter cycle, say 25 days, can be a sign of a short luteal phase, which may reflect a potential problem within the reproductive system; whereas a longer cycle can be the consequence of postponed ovulation, which suggests factors outside the reproductive system are impinging on a woman’s cycle. How do you know if the follicular phase is long or the ovulatory phase is short? To have any idea of the length of each phase we would have to look beyond cycle and menses length.

Since the reproductive system is so dynamically responsive to the other systems within the body, it is extremely valuable for all women, not just women trying to conceive, to know the nuances of each and every cycle. Shifts in your follicular or luteal phase can alert you to health issues long before common medically-defined symptoms prompt you to think about seeing a health professional. In addition, by starting to chart your cycles you may also observe changes in any of the three fertile signs (cervical fluid, cervical position, and basal body temperature) that can also provide insight into the health of other systems, such as digestive health. {For great programs to learn all the ins and outs of charting visit here}

I highly recommend making a simple Excel spreadsheet and keeping a printout by your bed. You can then include any factors you feel are relevant to your health personally. For example, I have tailored my chart to track my energy levels and sugar intake each day. While you can make notes in charting apps, you cannot get a sense of the trends unless you are looking at the chart as a whole.

If you prefer to use a charting app, I recommend Kindara or the online Justisse program. If you are you charting for pregnancy or contraceptive purposes, be cautious about any predictive features in apps as these apps fundamentally rest upon the notion of 28-day model and regularity that, as I have said, research has shown is not the biological reality. Your cycle will shift according to your whole body health and lifestyle each and every cycle, so a prediction of your fertile days can be inaccurate.

As an aside, in addition to the potential for inaccurate predictions, technology that forecasts undermines our body awareness and our attention to subtle shifts that are more natural than periodic patterns. Stepping away from the technology here will allow you to increase your awareness of your natural signals as well as decrease some of your screen-time — another bonus!

I want to reiterate that the important fact is that current research shows that the fluctuations in cycle and menses length are just as natural, if not more natural, than the 28-day model. By taking the time to be present and increase your sensitivity to the signals that are constantly happening, you will have a wealth of knowledge about your health. You and your health professional might refer to commonly held ideas about norms (i.e. the length of one’s cycle, menses, follicular phase, or luteal phase), but the more significant data will come from your notations on your own personal patterns. Might a short cycle or luteal phase be due to a hormonal imbalance? It is possible. But being out of alignment with the 28-day model does not necessarily mean you are unhealthy.

If your charting alerts you to some potential problems, for example, you are trying to conceive and observe that you have a short luteal phase, then you will be best served by working with a health professional who will look at your whole body health.

In upcoming posts I will expand upon this topic of ovarian function to delve deeper into what is currently believed to define fecundity. Some factors you will already be familiar with (eating healthily or limiting stressors) but I will go beyond the common conversations to explore why we see very healthy, relaxed women not conceiving and women struggling through poor nutritional and environmental situations yet becoming pregnant with no apparent problem. There will also be some factors that you will not likely have heard before. 

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[1] Amy Harris and Virginia Vitzthum, “Darwin’s Legacy: An Evolutionary View of Women’s Reproductive and sexual Functioning” Journal of Sex Research, 50 (2013), 207-246 (p. 208).

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