Factors associated with menstrual-related disturbances following SARS-CoV-2 vaccination: a Spanish retrospective observational study in formerly menstruating women

Background: A growing body of evidence suggests a potential link between the SARS-CoV-2 vaccine and menstrual changes in women who were menstruating at the time of vaccination. Nevertheless, the prevalence of this event in those with secondary amenorrhea for different causes, i.e. formerly menstruating women, remains unclear. It is plausible that, analogous to those observed in currently menstruating women, they experienced some degree of alteration in their reproductive health, defined here as menstrual-related disturbances.

Objective: The aim was to analyze this phenomenon and identify the factors associated with the occurrence of menstrual-related disturbances in this subpopulation. Study design: A retrospective observational cross-sectional study was conducted among adult Spanish in December 2021 using an online survey (N = 17,512). The present analysis includes a subpopulation of vaccinated and formerly menstruating women (N = 548). General characteristics, medical history, and adverse events following COVID-19 vaccination were recorded. Chi-square, Mann-Whitney U and McNemar mid-P tests were performed. Bivariate logistic regression was then used to identify the key factors influencing this unexpected event.

Results: In comparison with the first dose, significantly higher percentages of respondents experienced menstrual-related disturbances (dose 1: 38.5 percent vs. dose 2: 44.8 percent) after receiving the second one. Among them, those related to the length and flow stand out, being of long-term nature in about 17-20 percent of cases. Interindividual factors influencing this unexpected event after receiving the dose 1 may include weight, perimenopause, preexisting diagnoses of non-autoimmune rheumatic/articular conditions, use of hormonal contraceptives, suffering from other vaccine side effects - such as arm pain and the number of previous pregnancies; for dose 2, these factors may include suffering from menstrual-related alterations after receiving dose 1, as well as the use of hormonal contraceptives and perimenopause.

Conclusion: Formerly menstruating women might experience long-term menstrual-related disturbances following COVID-19 vaccination. Potential influencing factors include weight, perimenopause, rheumatic/articular conditions, hormonal contraceptives, vaccine side effects and previous pregnancies.