Gemma C Sharp , ^1,2 Abigail Fraser , ^1,2,3 Gemma Sawyer,¹ Gabriella Kountourides,⁴ Kayleigh E Easey , ^1,2 Gemma Ford,⁵ Zuzanna Olszewska,⁴ Laura D Howe,^1,2 Deborah A Lawlor,^1,2,3 Alexandra Alvergne^4,6 and Jacqueline A Maybin ⁷

• ¹ Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK,
• ² MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK,
• ³ NIHR Bristol Biomedical Research Centre, Bristol, UK,
• ⁴ School of Anthropology, University of Oxford, Oxford, UK,
• ⁵ Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK,
• ⁶ Institut des Sciences de l’E´volution, Universite´ de Montpellier, Montpellier, France and
• ⁷ MRC Centre for Reproductive Health, University of Edinburgh, Edinburgh, UK

Menstrual cycle features and the COVID-19 pandemic

Over 50% of the global population will experience menstruation, and menstrual disorders are extremely common and debilitating. 1 Problematic menstruation may cause anaemia, 2 has a significant negative impact on quality of life and is a huge socioeconomic burden for women, their families, health services and society. 3–7 Standardized parameters for typical menstruation have been defined by the International Federation of Gynecology and Obstetrics (FIGO) regarding menstrual frequency, duration, regularity and volume, and deviation from these may constitute abnormal uterine bleeding. 8 Features of the menstrual cycle are also increasingly being recognized as ‘vital signs’— acting as both indicators and possible determinants of broader health and well-being.9 For example: irregular and long menstrual cycles have been associated with a greater risk of premature mortality,10 and infrequent or absent menstruation can be an indicator of reduced fertility,3 which itself can be associated with a number of chronic conditions. 11 Since the beginning of the COVID-19 pandemic, there have been accumulating discussions on social media and blogs indicating that women have experienced menstrual changes, including altered menstrual duration, frequency, regularity, and volume (heavier bleeding and clotting), increased dysmenorrhoea and worsened premenstrual syndrome (PMS) (e.g. Morgan 202112). More recent anecdotal reports of menstrual changes after vaccination for COVID-19 have fuelled vaccine hesitancy or refusal. There is an important public health imperative for accurate scientific investigation of these phenomena.

Unfortunately, questions about menstruation have been excluded from most large-scale COVID-19 studies (including vaccine trials), so it is currently unclear how many women have experienced menstrual cycle changes, how long these changes persisted, whether menstrual changes reflect common and expected fluctuation in menstrual features over time or the impact of an exposure (e.g. pandemic restrictions, infection/illness, treatment, vaccine) and what exactly this exposure is. Given this complexity, the impact of any menstrual changes since the start of the pandemic is also unclear. Even outside the context of COVID-19, studying menstrual cycle features is challenging. Normal variation exists within women over the lifespan and between women in relation to characteristics such as history of infertility, parity, body mass index (BMI) and exercise. 13 In addition, menstrual cycle features such as volume, pain and PMS symptoms are subjective and data are necessarily collected, in health care as well as research, by self-report.

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