You may be yearning for some
actual scientific data after months of cycling through anecdotal claims that
Covid-19 vaccines may affect menstrual cycles and calls for more studies.
Finally, a serious scientific study has been published in Obstetrics & Gynecology,
an actual medical journal. And, yes, the research reveals that Covid-19
vaccination may cause specific changes in your menstrual cycle. However, before
you put a period at the end of that sentence and jump to conclusions, keep in
mind that the changes are likely to be minor and temporary based on the
report's results.
The menstrual cycles of 3,959 study participants were tracked for
six processes using "Natural Cycles." Now, "Natural Cycles"
may sound like a bicycle made of leaves, but it's a female fertility app
approved by the US Food and Drug Administration. Each study participant was
assigned to two groups: vaccinated or unvaccinated for comparison purposes.
For the 2,403 participants in the vaccinated group, the six
consecutive cycles consisted of the three successive cycles right before their
getting Covid-19 vaccine doses and then the three consecutive cycles
immediately after vaccination. Fifty-five percent of those vaccinated got the
Pfizer-BioNTech vaccine, percent the Moderna vaccine, and 7% the Johnson &
Johnson/Janssen vaccine. The study followed the remaining 1,556 people in the
unvaccinated group through six cycles. Alison Edelman, MD, MPH directed the
research; Emily R. Boniface, MPH; Eleonora Benhar, Ph.D.; Leo Han, MD, MPH; Kristen
A. Matteson, MD, MPH, Carlotta Favaro, Ph.D.; Jack T. Pearson, Ph.D.; Blair G.
Darney, Ph.D., MPH From Oregon Health & Science University in Portland,
Oregon.
The demographics of the two study groups were pretty similar. In
the Northeast, 20% of the vaccinated versus 13% of the unvaccinated lived, and
in the Western United States, 37% of the vaccinated versus 34% of the
unvaccinated lived. Around 54% of vaccinated folks identified as White,
compared to about 47% unvaccinated. The participants were between the ages of
18 and 45. Those who received vaccinations were slightly older, with 34% being
between 30 and 34, compared to 24% of those who did not receive vaccines. More
significant percentages of the vaccinated versus unvaccinated hadn't had babies
previously (79% vs. 69%) and were college-educated (77% vs. 60%). Of note, all
had prior histories of fairly regular cycle lengths.
So what did the study find? Those who got their first dose of the
Covid-19 vaccine had to wait, wait, wait for their next period for an average
of 0.71 days longer than they did before vaccination. In other words, the
length of their menstrual cycle, or the time between bleeding episodes, tended
to increase slightly, with most increases falling between 0.47 and 0.94 days.
The average increase for those who got their second dose was 0.91 days, with
most increases ranging from 0.63 to 1.19 days.
Your menstrual cycle isn't an atomic clock, of course. It's not
even like a game show clock. If you use your menstrual cycle or any other bodily
function alone to keep track of time, you're probably going to miss a whole lot
of meetings. Your menstrual cycle will not always be the same length and will
vary in size from month to month to different degrees. As a result, it's not
surprising that those not vaccinated in the study had some fluctuations.
Between the first three measured weeks and the second three measured weeks, the
unvaccinated group's cycle length rose by 0.07 days on average. The majority of
the changes ranged from a 0.22-day decrease to a 0.35-day increase.
When the study's vaccinated and unvaccinated participants were
compared, vaccination was still linked to lengthening the menstrual cycle.
After the first dose, those vaccinated had a 0.64-day increase in cycle length,
with most increases ranging from 0.27 to 1.01 days, and a 0.79-day increase
after the second dose, with most increases ranging from 0.40 to 1.18 days. The
average differences were less than the time it would take to watch all three
Lord of the Rings movies.
Such changes were still well within the range of natural
variation. Doctors usually don't consider changes of less than a week to be
clinically significant. Although 5.2 percent of the vaccinated group and 4.3
percent of the unvaccinated group had cycle length changes of eight days or
greater, the vast majority of the vaccinated did not experience such clinically
significant changes in cycle length. However, there was no statistically
significant difference between the vaccinated and the unvaccinated.
Even when such cycle lengthening was seen, such increases appeared
to be only temporary. The bulk of the observed increases in the vaccinated
occurred in the cycle immediately following vaccination (i.e., the fourth
cycle). By the sixth menstrual cycle, only two cycles later, cycle lengths for
the vaccinated group, for the most part, reverted to where they had been before
vaccination.
All of the following changes were made to the length of the
menstrual cycle or the time between bleeding episodes. The researchers didn't find
any consistent changes after vaccination in menses length, which is the number
of days that study participants experienced bleeding.
So, what does all of this mean? It's not surprising that some
changes in menstrual cycle length happened in the weeks that followed
vaccination. After all, your menstrual cycle depends on chatter among different
parts of your body, such as your hypothalamus, pituitary glands, ovaries, and
the lining of your uterus. These body parts communicate with each other using
hormones such as estrogen, progesterone, gonadotropin-releasing hormone (GnRH),
follicle-stimulating hormone (FSH), and luteinizing hormone instead of text
messages, emojis, and TikTok videos (LH). Changing levels of these different
hormones lead to the other steps in your menstrual. And lots of various
physical, emotional, and environmental stresses around you can affect these
hormone levels.
Think of vaccination as a wrong date for your immune system when
stressed. Vaccines introduce spike proteins to your immune system by providing
tiny little blueprints to your body's cells, allowing them to create them.
These are the spike proteins that stud the surface of the severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2), making it look like the end of
a BDSM mace, not that you would know anything about such a thing. Once your
immune system meets these spike proteins, it then effectively says, "oh,
no, you didn't," and mounts a response against the spike protein. This is
analogous to what happens when your Tinder date shows up with a lint roller and
an anvil to your first meeting in a restaurant. Your immune system then is
better prepared to deal with any further encounters with the spike protein,
just like you'll be better prepared the next time a Tinder profile says,
"really like lint rollers and anvils."
Such experiences can bring some momentary stress to your body.
This, in turn, could have a short-term impact on your hormone levels as well as
the lining of your uterus. Time is crucial when it comes to body changes and
watching The Bachelor or The Bachelorette. Short-term changes happen all the
time, like when you "accidentally" change the channel on your TV to
The Bachelor or The Bachelorette. Longer-term, consistent adjustments may be
more critical. Receiving one, two, or even three doses of the Covid-19
vaccination is not the same as daily taking a prescription or supplement. A
vaccine's contents should leave your body relatively fast.
Does this study once and for all rule out the possibility that
Covid-19 vaccines can have any other effects on your menstrual cycle? No, a
single scientific study is never sufficient to establish anything. And this
study had its limitations. Although 3,959 may seem like a large number when it
comes to the number of people in front of you in the restroom line, it's a
reasonable but not an enormous sample size. The study's participants were not
as diverse as the general population, and those with more variable menstrual
cycles were excluded. Other aspects of menstruation and processes, such as
related symptoms and bleeding characteristics, were not studied before and
after vaccination by the researchers. More research is needed to confirm the
study's findings and shed more light on possible links between immunization and
your menstrual cycle.
Nonetheless, results from this study did provide even more reassurance that the Covid-19 vaccines won't substantially affect your menstrual cycle or fertility. There's no indication that such small temporary changes in your menstrual cycle should affect your fertility in any way. All of this suggests that going with the flow when getting vaccinated against Covid-19 has no real risk.