OHSU study finds COVID vaccines can impact menstrual cycle length
PORTLAND, Ore. (KOIN) – A new Oregon Health & Science University study found that slight, temporary changes in menstrual cycles are associated with the timing of COVID-19 vaccinations.
The study, published Wednesday in the Obstetric & Gynecology journal, found that people who received a COVID shot in the first half of their menstrual cycle are more likely to experience cycle length changes than people who received a vaccine in the second half of their cycle.
The study builds on work from the same research team that found an association between COVID-19 vaccines and cycle length. However, researchers said this study furthers understanding of how vaccination timing impacts cycle changes.
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“Understanding these changes on a population level allows us to more effectively counsel patients about what to expect with a COVID-19 vaccine,” said Dr. Alison Edelman, the study’s lead author and professor of obstetrics and gynecology and division director of Complex Family Planning in the OHSU School of Medicine. “We hope this work helps validate the public’s experiences and ease fears and anxiety around vaccination.”
Researchers used data from nearly 20,000 users of the FDA-cleared birth control app Natural Cycles to determine whether vaccine timing is associated with cycle length. OHSU notes researchers received permission to use the de-identified data from the app’s users.
Researchers compared three groups including people vaccinated in the follicular phase – the first menstrual cycle phase when the body collects follicles that have the potential to release an egg during ovulation—along with people vaccinated in the luteal phase – the second phase starting after ovulation – and an unvaccinated control group.
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Researchers found that people who were vaccinated in the follicular phase experienced a one-day increase in cycle length, on average, compared with their pre-vaccinate cycle average. The changes usually resolved in the following cycle after vaccination.
Despite evidence showing that the vaccine is associated with temporary cycle changes, the exact “biological mechanism” for the change is still unknown, OHSU says.
“We are constantly learning about how our bodies work together, but we do know the immune and reproductive systems interact closely with one another,” Edelman explained. “Based on this relationship, it is certainly plausible that individuals may see temporary changes in their menstrual cycle due to the immune response that vaccines are designed to produce.”
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The experts emphasized that these findings should not be a cause for concern and should provide reassurance that if people experience changes in cycle length, they are likely to be small and temporary.
People who experience prolonged changes in menstruation should seek guidance from their doctor, OHSU said.
Because the data was gathered from people with regular menstrual cycles before the vaccine, OHSU says more research is needed to establish any differences for people who have irregular cycles.
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Researchers also hope to better understand how vaccination impacts menstrual-related symptoms and flow.
“Historically, menstruation has not been prioritized in scientific and medical research, which leaves individuals who menstruate with a lot of unanswered questions, especially when they are experiencing something that’s not ‘normal’ for their body,” Edelman said. “Menstruation is a key indicator of fertility and overall health, so understanding these changes is very important to us as reproductive health researchers and to our patients.”
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