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Abstract
Objectives To identify whether covid-19 vaccines are associated with menstrual changes in order to address concerns about menstrual cycle disruptions after covid-19 vaccination.
Design Global, retrospective cohort study of prospectively collected data.
Setting International users of the menstrual cycle tracking application, Natural Cycles.
Participants 19 622 individuals aged 18-45 years with cycle lengths of 24-38 days and consecutive data for at least three cycles before and one cycle after covid (vaccinated group; n=14 936), and those with at least four consecutive cycles over a similar time period (unvaccinated group; n=4686).
Main outcome measures The mean change within individuals was assessed by vaccination group for cycle and menses length (mean of three cycles before vaccination to the cycles after first and second dose of vaccine and the subsequent cycle). Mixed effects models were used to estimate the adjusted difference in change in cycle and menses length between the vaccinated and unvaccinated.
Results Most people (n=15 713; 80.08%) were younger than 35 years, from the UK (n=6222; 31.71%), US and Canada (28.59%), or Europe (33.55%). Two thirds (9929 (66.48%) of 14 936) of the vaccinated cohort received the Pfizer-BioNTech (BNT162b2) covid-19 vaccine, 17.46% (n=2608) received Moderna (mRNA-1273), 9.06% (n=1353) received Oxford-AstraZeneca (ChAdOx1 nCoV-19), and 1.89% (n=283) received Johnson & Johnson (Ad26.COV2.S). Individuals who were vaccinated had a less than one day adjusted increase in the length of their first and second vaccine cycles, compared with individuals who were not vaccinated (0.71 day increase (99.3% confidence interval 0.47 to 0.96) for first dose; 0.56 day increase (0.28 to 0.84) for second dose). The adjusted difference was larger in people who received two doses in a cycle (3.70 days increase (2.98 to 4.42)). One cycle after vaccination, cycle length was similar to before the vaccine in individuals who received one dose per cycle (0.02 day change (99.3% confidence interval −0.10 to 0.14), but not yet for individuals who received two doses per cycle (0.85 day change (99.3% confidence interval 0.24 to 1.46)) compared with unvaccinated individuals. Changes in cycle length did not differ by the vaccine’s mechanism of action (mRNA, adenovirus vector, or inactivated virus). Menses length was unaffected by vaccination.
Conclusions Covid-19 vaccination is associated with a small and likely to be temporary change in menstrual cycle length but no change in menses length.
- COVID-19
Data availability statement
No data are available. Data were accessed under a data use agreement with Natural Cycles USA Corp, New York and are not available to third parties.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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Data availability statement
No data are available. Data were accessed under a data use agreement with Natural Cycles USA Corp, New York and are not available to third parties.
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Footnotes
Contributors AE, BGD, and ERB report substantial contributions to the design, dataset preparation and readiness, analysis, interpretation of the results, drafting the work, and approval of the version to be published. EB, JTP, and AVL report substantial contributions to the design, acquisition and interpretation of the data, revising it critically for important intellectual content, and final approval of the version to be published. KAM, VM, and STC report substantial contributions to the design or the work, interpretation of results, revising the work critically for important intellectual content, and final approval of the version to be published. All authors are accountable for all aspects of the work; AE serves as the guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted. Transparency: The lead author (the guarantor) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.
Funding Research reported in this publication was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the NIH Office of Research on Women's Health. NIH NICHD089957 Supplement. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The funders had no role in considering the study design or in the collection, analysis, interpretation of data, writing of the report, or decision to submit the article for publication.
Competing interests AE reports honoraria and travel reimbursement from the American College of Obstetricians and Gynecologists, World Health Organization, and Gynuity for committee activities and honorariums for peer review from the Karolinska Institute. AE receives royalties from UptoDate. Oregon Health and Science University (OHSU) receives research funding from OHSU Foundation, Merck, HRA Pharma, and the National Institutes of Health for which Alison Edelman is the principal investigator. BGD reports honorariums and travel reimbursement from the American College of Obstetricians and Society of Family Planning for board, committee, and mentorship activities. OHSU receives research funding from Merck/Organon and Office of Population Affairs/Department of Health and Human Services for which BGD is the principal investigator. OHSU receives research funding from OHSU foundation, the Bill & Melinda Gates Foundation, American Board of Obstetrics and Gynecology, American Society for Reproductive Medicine, and the National Institutes of Health for which Leo Han is the principal investigator. EB, AVL, and JTP are employees of Natural Cycles. Natural Cycles received cost reimbursement from grant funds for data processing and secure transfer. KAM reports honorariums and travel reimbursement from the American Board of Obstetrics and Gynecology and travel reimbursement from American College of Obstetricians and Gynecologists. Women and Infants Hospital received funding from Myovant for consulting work done by KAM on outcomes measures for heavy menstrual bleeding. VM reports research funding from Borne, payment for acting as an external examiner for the Universities of Cambridge, Leeds and Swansea, and royalties received for contribution to Immunology 9th edition (Elsevier). STC is the editor-in-chief of BMJ Sexual and Reproductive Health and reports an honorarium from Gedeon Richter Nordics for a lecture on contraception. ERB declares no competing interests.
Provenance and peer review Not commissioned; externally peer reviewed.
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