In a recent study published on the medRxiv * prepress server, researchers in the United States (USA) estimated the association between coronavirus 2 (SARS-CoV-2) vaccination of severe acute respiratory syndrome and menstrual cycle duration in a large cohort of participants. across the US. They focused their assessments on menstrual variations due to the type of coronavirus disease vaccine 2019 (COVID-19) and the timing of its administration.
Study: Covid-19 vaccination and menstrual cycle duration in the Apple Women’s Health study. Image credit: VonaUA / Shutterstock
Fund
In April 2022, more than 11,000 women reported a menstrual-related problem in the U.S. Vaccine Adverse Event Information System (VAERS). Adverse outcomes included alterations in menstrual features, including cycle length, increased bleeding, and menstrual irregularities. This anecdotal evidence prompted researchers to improve their understanding of these associations and inform physicians to advise women on COVID-19 vaccination.
About the study
In the present study, the researchers used data from the Apple Women’s Health Study (AWHS) to assess the temporal evolution of the relationship between COVID-19 vaccination and menstrual cycle length. They compared the length of the menstrual cycle before vaccination, the cycles in which a vaccine dose was administered, and the cycles after vaccination against COVID-19. All study participants were women over the age of 18 living in the United States who had menstruated at least once, could communicate in English, and owned an iPhone with a compatible version of iOS.
These women provided the initial menstrual status along with their demographic details at the time of enrollment. After enrollment, the researchers conducted a monthly survey about their menstrual health. The team from the National Institute of Environmental Health Sciences, Health, Apple Inc. and the Harvard TH Chan School of Public Health asked about the date of the first and second dose of vaccine, the type of vaccine and symptoms within 48 hours of vaccination. participants who received a vaccine against COVID-19 after September 2021. Participants used the Apple Health app or a third-party app to track their menstrual cycle with the associated dates.
The team limited the analysis of the study to four cycles after vaccination. In addition, they classified vaccination as having occurred during the follicular or luteal phase of a menstrual cycle to assess the impact of dose timing within a menstrual cycle. Because previous studies have suggested a nonlinear relationship between age and the length of the menstrual cycle, the team categorized each participant based on age for this analysis. In addition, they stratified participants as low weight, normal, overweight, or obese based on their self-reported body mass index (BMI). The study included months and years of the cycle to control for the effect of seasonality and pandemic stressors.
In addition, the researchers included participant identification as a fixed matter-level effect in conditional linear regression models to estimate the difference between the covariate-adjusted woman and the 95% (95% CI) confidence intervals in the average duration of the cycle. Finally, the model compared the vaccinated and post-vaccination cycles of each participating woman with their pre-vaccination cycles (control cycles).
According to the International Federation of Gynecology and Obstetrics, a menstrual cycle that lasts more than 38 days is a long cycle. The team used generalized estimation equations (GEEs) to fit a logistic regression model that calculated the probability ratio (OR) and the 95% CI for the association between COVID vaccination. -19 and the probability of a long cycle in vaccinated participants compared to unvaccinated participants. Finally, the team used two sensitivity analyzes to assess the robustness of their primary analysis.
Study results
The current analysis of the study covered 128,094 menstrual cycles of 9,652 participants, who recorded an average of 13 cycles. In addition, the mean standard deviation in cycle duration for any individual woman was 4.2 days. Of all vaccinated women, 55%, 37%, and 7% had received the Pfizer-BioNTech, Moderna, and Johnson & Johnson / Janssen (J&J) vaccine, respectively.
All vaccinated women only had slightly longer menstrual cycles than their pre-vaccination cycles. On average, the single dose of the J&J vaccine increased the duration of the cycle by 1.26 days. In addition, the observed increase in mean menstrual cycle duration was negligible and non-persistent depending on the number of vaccine doses (0.50 vs. 0.39 days after the first and second vaccine doses). In addition, the length of the menstrual cycle returned to pre-vaccination mean values between 0.14 days and -0.25 days between the first and fourth menstrual cycles after vaccination.
However, the authors observed an association between vaccination and the phases of the menstrual cycle. Subsequently, vaccine doses received in the follicular phase increased the mean cycle time observed in the results of the preliminary study. In addition, when a woman received the second dose of vaccine in the luteal phase, the subsequent menstrual cycle, on average, was shorter. The covariate-adjusted mixed-effects model and GEE results did not vary much between vaccinated and unvaccinated participants. The mean duration of the menstrual cycle was 0.24 days for the former, and the ORs for GEE were 1.20.
Conclusions
Current work showed that vaccination against COVID-19 was safe for menstruating women, with no adverse effects on fertility. Although vaccination slightly increased the length of the menstrual cycle; however, it remained within the natural variability observed in the study population. The alteration in cycle length after vaccination was probably due to vaccine doses received in the follicular phase of the menstrual cycle. However, these changes gradually decreased with each cycle, and none persisted over time. In conclusion, since the changes observed in the menstrual cycle were only minor and transient, women should not be deterred from COVID-19 vaccination.
* Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guided by clinical practice or health-related behavior, or treated as established information.
Magazine reference:
- Elizabeth A Gibson, Huichu Li, Victoria Fruh, Malaika P Gabra, Gowtham Asokan, Anne Marie Z Jukic, Donna D Baird, Christine L Curry, Tyler Fischer-Colbrie, Jukka-Pekka Onnela, Michelle A Williams, Russ Hauser, Brent A Coull , Shruthi Mahalingaiah, medRxiv prepress,