Missing or Irregular Periods: What the Research Says

By Marta Han, co-founder of The Fertility Class, certified Aviva Method instructor, yoga teacher and health coach, who got her own cycle back after hypothalamic amenorrhea. 

Last updated October 2026.

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In short: A missing or irregular period is a signal, not a diagnosis. The most common causes are low energy availability and stress (hypothalamic amenorrhea), PCOS, thyroid changes and coming off the pill. Eating enough, easing back on intense training and gentle, targeted movement help many cycles return, and anyone who has missed three or more periods should see a doctor to rule out other causes.

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Before I was anything else, I was a competitive ballroom dancer. Years of movement, discipline and training my body. What I did not understand until much later was what that kind of training was doing to my hormones and my fertility.

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My cycle stopped. Not gradually. It simply stopped. Looking back, I was underweight and restricting what I ate, in an industry where looking very thin was normal and expected. My body had quietly decided that reproduction was not the priority. That is what hypothalamic amenorrhea is: a decision the body makes when it concludes, rightly or not, that conditions are not safe for a pregnancy.

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Discovering the Aviva Method changed everything for me. I practiced the exercises consistently, and within a few months my cycle returned and became regular. That experience led me to complete the two-year Aviva Method instructor certification and, eventually, to co-found The Fertility Class. Ten years of teaching later, cycle regulation is still one of the main reasons women come to us.

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Here is what I know about why cycles stop, and what helps bring them back.

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Almost always, the body is responding to something. It is not a malfunction. It is a response.

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The most common drivers are low energy availability, which does not require dramatic restriction, only too little fuel for what you ask of your body; high psychological stress; and too much high-intensity exercise. They can appear alone or together, and the body reads all three as a sign that now is not the right time for a pregnancy.

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When that signal is strong enough, the brain slows the hormonal cascade that leads to ovulation. No ovulation, no period. It is protective by design. The difficulty is that the body cannot tell the difference between a genuine threat to survival and a hard training block combined with a calorie deficit and a demanding job. It simply responds to the signal.

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Hypothalamic amenorrhea is the clinical name for a missing period caused by this kind of stress response, as opposed to other causes such as PCOS, thyroid conditions or early menopause. It is more common than most people realize, and it appears disproportionately in women who are high-achieving, athletic and driven.

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The most important thing to know is that it is reversible. When the signals change, the body can and does restart the cycle. The Endocrine Society’s 2017 clinical practice guideline on functional hypothalamic amenorrhea, published in the Journal of Clinical Endocrinology and Metabolism, identifies energy availability, exercise load and stress as the main drivers, and recommends addressing them as the first line of treatment.

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Yes, for some women. This is the hardest part to hear if you exercise seriously and love it.

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High-intensity, high-volume training, particularly in endurance sports, competitive dance and other aesthetic disciplines, is a well-documented cause of lost cycles. The American College of Sports Medicine’s position stand on the female athlete triad, published in Medicine and Science in Sports and Exercise, describes how low energy availability in active women disrupts the menstrual cycle. The mechanism is straightforward: heavy training raises stress hormones and creates an energy deficit, and both suppress the hormonal signals that drive ovulation.

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For many of the women I work with, the hardest part of recovery is accepting that the answer may be to do less, not more. Restorative movement supports a returning cycle. Intense training works against it.

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Low-impact, deliberate movement that engages the pelvic and deep abdominal muscles can support a returning cycle without the cortisol spike that comes with high-intensity work.

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The goal is to send the body a signal of safety rather than stress. The Fertility Class sequences are designed for exactly this. They are low-impact by intention, and they engage the pelvic and abdominal muscles in a way that supports circulation to the reproductive organs. In a 2023 study in the Journal of Clinical Medicine, Kovács and colleagues used Doppler ultrasound to measure uterine artery blood flow before and after Aviva Method exercise, the foundation of The Fertility Class, and found significant changes, evidence that these sequences affect blood flow to the pelvic organs rather than offering general conditioning alone. Read more in The Importance of Pelvic Blood Flow for Fertility.

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This is the practice I returned to while recovering my own cycle, and it is what we build The Fertility Class around.

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Post-pill amenorrhea is different from hypothalamic amenorrhea, but the two overlap, and the overlap is worth understanding.

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The pill suppresses ovulation by design. When you stop, your body has to re-establish its own hormonal rhythm, and for most women that happens within a few months, though for some it takes longer.

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What the pill often conceals are the patterns that were there before it: irregular cycles, signs of PCOS, or a cycle that was already disrupted. If your cycle was irregular before you started the pill, it is likely to be irregular when you stop. The pill does not reset anything. It pauses it.

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What helps post-pill recovery overlaps with what helps hypothalamic amenorrhea: reduce the physical stressors, support the body as its hormones recalibrate, and choose movement that helps rather than disrupts. If PCOS may be part of your picture, read PCOS, Exercise and Fertility.

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It depends, and I will not give you a timeline that leaves you feeling you are failing.

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The factors that matter most are how far the underlying stressors are reduced, how consistently you practice supportive movement and how suppressed the cycle was to begin with. Women I have worked with have seen their cycles return anywhere from six weeks to several months. One returned period is not yet a regular cycle. Regularity takes longer and depends on consistency. That is not unusual. It is simply how the body works.

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A missing period is what led me to the Aviva Method. It is why I became an instructor and, eventually, co-founded The Fertility Class with Zsofia. Between us, we have 25 years of teaching this method to women facing exactly these challenges, and we built the program because we both wished it had existed when we needed it. Since then, we have helped hundreds of women restore their cycles after six, twelve and even twenty-four months or more without a period.

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The Fertility Class is an on-demand online program practiced at home, designed to sit alongside any medical care you already receive. If your period has been absent for several months, seeing a doctor to rule out other causes is the right first step, and the program is designed to complement that process, never to replace it.

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I want to leave you with genuine reassurance. With changes to how you eat, move and manage stress, getting your cycle back is very much possible, and so is a fertile body and a healthy pregnancy. We have seen it again and again at The Fertility Class, and I would love for you to experience it yourself.

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• Gordon et al., Journal of Clinical Endocrinology and Metabolism, 2017: Endocrine Society clinical practice guideline on functional hypothalamic amenorrhea
• Physical activity, vigorous exercise and fertility
• Stress and reproductive hormone signalling
• Kovács, Hegyi and Szőke, Journal of Clinical Medicine, 2023: Aviva Method exercise and uterine artery blood flow

More research on our Studies page