Research Update 3: Fertility, Menstruation, COVID-19 and Vaccination

Below is the transcript of the video and audio research update I recorded on 20th Sept 2021 on the topic of fertility, menstrual changes, COVID-19 and vaccination against COVID-19. This information is information only, and does not take the place of individualised advice and consultation with your medical team. I hope you find this useful, and please feel free to share this resource with anyone you think might be interested.


Hello, my name is Anna Cusack, I am an author, a doula, Certified Motherhood Studies Practitioner, and parent mentor. I have uni post-graduate qualifications in Clinical Exercise Physiology specialising in rehabilitation and I also spent many years working as a health professional in community and hospital settings. This is the third research update I have recorded (the first was on lactation and vaccination against COVID-19, the second was on pregnancy), but in this video I will be discussing the academic, scientific research and researcher perspectives published to date in relation to fertility, menstrual cycles and COVID-19 vaccination.

Obviously there are limitations here – I am one person not a team of professional researchers, and I can only give you information from studies that have been published in English. The reading I have done is comprehensive but I am not trying to position myself as an expert in this area. I am relaying the findings of the people who are actually the experts in words that you can hopefully understand.

The date of this recording is the 20th of September 2021. All sources I mention are referenced in the video or audio notes. As time passes, new information will come to light as more studies are released, so I would encourage you to stay up to date with that. Using the Google Scholar search engine is the easiest way for the majority of people to access the abstracts or summaries of research papers, and in many cases the full text of the articles are freely available as well.

As at the time of this research review being recorded, there is much confusion and hesitation regarding vaccination amongst those who are trying to become pregnant or concerned for their future fertility, both within Australia and abroad. In this video I will only be speaking to Pfizer and Moderna mRNA vaccines and AstraZeneca (also known as Vaxzevria) because those are the 3 types available here in Australia where I am situated.

The advice we’ve been receiving over the last six months in the space of conception, gestation, pregnancy and beyond has been confusing. There has also been much speculation around vaccination and its potential effect on fertility and menstrual cycles, particularly on social media.

As is the theme with these presentations I have put together and medical research in general, it’s important to note that people who were pregnant or actively trying to become pregnant were not purposefully included in clinical trials for the various COVID-19 vaccines available. This is standard practice in drug research.

Some people who conceived just after or just before being vaccinated and also consented to being followed up by researchers, and I will get to those study groups in a moment.

Before that though, it’s worth noting that in terms of drug research itself, medications generally go through what’s called a “developmental and reproductive toxicity study” in animals. In August 2021, Bowman and colleagues released the results of the BNT162b2 vaccine (that’s the Pfizer) developmental and reproductive toxicity study. So in this study they gave female rats the human size dose of Pfizer (on a dose to bodyweight ratio, that is equivalent to a human being given 300 doses of the vaccine instead of one). They also gave them 4 doses of that quantity, at 21 and 14 days before they mated, and gestation days 9 and 20. So on a body size basis, the rats received the equivalent of 1200 doses, when humans would only receive 2. At the end of the gestational period, the authors performed caesarean sections on half of the female rats and dissected the babies. The other half of the rat subjects gave birth to their young as rats generally do, and were monitored to the end of the lactation.

The researchers state, and I quote: “There were no effects of BNT162b2 on female mating performance, fertility, or any ovarian or uterine parameters nor on embryo-fetal or postnatal survival, growth, physical development or neurofunctional development in the offspring through the end of lactation.” These results will allow them to move onto formal clinical trials where humans who are trying to conceive can be included and studied along their whole fertility and gestational journey, rather than us just relying on retrospective data from humans who’ve volunteered to have their doses already. This will obviously take a while though, because human babies take much longer to grow than rat babies do!

So what do we know about COVID-19, vaccination against it and human fertility? The straight up answer is “not heaps”, but I’ll tell you what we do know.

As I mentioned before, we know that small numbers of people who were in the initial clinical trials of the vaccines either fell pregnant unexpectedly during the trial, or were in the early stages of pregnancy and likely didn’t know they were pregnant yet. A paper from July 2021 by Garg, Shekhar Sheikh and Pal tells us that there were 11 people who received the Pfizer just before or just after getting pregnant, and 6 people who received the Moderna. None of those people experienced miscarriages.

Another study I have spoken about in the previous research update on pregnancy is called “Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons”. It is a 2021 paper by Shimabukuro and colleagues, and it is following people who identified as being in the periconception period or pregnant when they had their first vaccination between 14th December 2020 and 22nd Feb 2021. These were mostly white healthcare workers in the USA.

There are 3958 people involved in that study, and 92 of them (so that’s 2.3%) had at least one, and potentially both, of their Pfizer or Moderna vaccinations in the periconception period, which they define that time period as from 30 days before the start of the last menstrual period until ovulation. Now these are small numbers and we don’t have complete data from those people yet because not enough time has passed, some of them won’t be due until November this year, so all we can really take from that is that some people are still getting pregnant once they’ve had one, if not two, vaccination shots.

There is another paper by Zauche and colleagues from August 2021, and I actually didn’t come across this paper in preparing the pregnancy research update, but it tracked 2456 pregnant persons who received one or both mRNA vaccination doses either in the six weeks prior to conception or up until 20 weeks gestation were included in the study.

So the first thing is that this one by Zauche and colleagues is a pre-print paper, that is it hasn’t undergone peer review by other experts in the field yet. The second is that people did get pregnant after having a vaccination close to conception. The third is that when they followed up their participants at 20 weeks and ran the data, they found a 14.1% raw spontaneous abortion (that means miscarriage) rate. When they used direct age standardization to a reference population (so that’s kind of like an imagined control group from existing data sets), they found the rates of loss between 6 to 20 weeks were actually a bit lower at 12.8%. It sounds weird but researchers generally don’t include pregnancies at less than 6 weeks in their loss calculations, which seems really odd on face value but at least the data is comparable.

So just to clarify, those initial 14.1% miscarriage rate and 12.8% standardized loss rate might sound high but between 11-16% is considered a pretty standard rate of pregnancy loss in the developed world prior to 20 weeks. So this paper tells us that people did get pregnant after having at least their first dose, and being vaccinated pre-conception or in the first trimester does not seem to increase the risk of miscarriage. Obviously more data is needed here but this is a good start.

There are very few papers looking at fertility directly, and that is again because they needed to do those developmental and toxicity studies in rats I described earlier before it got the green light to do human-specific fertility studies. So the paper I am referring to is by Safrai and colleagues and was conducted in Israel, and it’s called “Stopping the misinformation: BNT162b2 COVID-19 vaccine has no negative effect on women’s fertility”. That’s a pretty big title considering it’s a small study, and it has various limitations, but I’ll explain it to you.

First thing here is that this is a pre-print paper, which means it hasn’t had full peer review by other experts in the field yet. This needs to happen before it is officially published in a medical journal.

This study is an odd one because it’s looking at fertility data for couples who were patients at an Israeli hospital’s IVF clinic. So most couples using IVF already have something going on with infertility, but not all because not all couples have compatible body parts to make a baby. 47 of their female clients were involved in the study. These women had IVF cycles before vaccination, and also after they’d had their vaccination, and the study looked for any changes in the number of eggs retrieved, the number of mature eggs, and the fertilization rate of those eggs in the lab as per the IVF process pre and post vaccination. They then looked at the embryos for number and quality before and after vaccination too. In short, there were no changes in any of those measures pre and post vaccination. The authors state “These findings therefore are the first step in showing that the BNT162b2 vaccine [that’s the Pfizer] has no effect on IVF treatment parameters nor on the pregnancy rate” from IVF.

While they were at it, Safrai and colleagues also wrote a paper titled “BNT162b2 mRNA Covid-19 vaccine does not impair sperm parameters”. This one is also a pre-print, so not peer-reviewed yet. They tested samples from 29 men with normal spermogram results pre-vax and 14 men with abnormal spermogram results pre-vax, and compared this to the quality and quantity of sperm produced by each patient post-vax. They found no differences pre- and post-vaccination.

Interestingly in this study they refer to another paper by Gacci et al. from March 2021 called “Semen impairment and occurrence of SARS-CoV-2 virus in semen after recovery from COVID-19”. They reviewed samples from 43 sexually active men who’d recovered from COVID-19. They found a quarter of these, so 11 men who’d recovered had problems in their sample. 8 of them had no sperm in the seminal fluid, and 3 had low sperm counts. Unfortunately they don’t provide a control group or any follow up data to see how long it took for the sperm counts recover, or if they did at all, they just mention that these rates of abnormal samples are well above the general population expected ranges. They also found worse semen sample results were associated with worse bouts of COVID-19 symptoms. So I realise most of you came here to listen about female fertility and vaccination, but sperm is also required to make a baby so I think this paper on male fertility and the effect of disease itself is worth mentioning, particularly if those worse symptoms are likely avoidable through vaccination.

I’m going to look at two prominent claims regarding vaccine dangers to fertility, and then I’m going to look at menstrual changes, so if that’s what you’re waiting to hear, bear with me.

One thing that has been circulating is that the mRNA vaccines target a protein called syncytin-1, which is needed for formation of the placenta and continued pregnancy. The rumour says that there is no mechanism to stop the destruction of syncytin-1 once it has commenced by way of vaccination.

Ok, so let’s look at the info around this. First of all, all proteins are made up of smaller building blocks called amino acids. There are 20 amino acids, and every protein we come across is made up of those 20 put together in all different orders and combinations.

The mRNA vaccines work by inserting mRNA into the cells. That mRNA is like a recipe, that tells the body how to make the “spike protein” made by the SARS-CoV-2 virus that causes the COVID-19 disease. So your body makes a small amount of spike protein in response, your immune system then attacks it by making new antibodies against it, so that if you get coronavirus, you have some of those antibodies ready to go to fight it.

So back to Syncytin-1, the protein needed for the placenta. It is made up of 538 amino acids. The protein targeted by the Pfizer vaccine only shares a sequence of 4 of those 538. Lu-Culligan and Iwasaki from Yale School of Medicine wrote in the New York Times in January 2021 that “Our team compared the coronavirus’s spike protein to placental syncytin-1, and we found no notable similarity between their amino acid sequences”. They also say they analysed blood serum from women with COVID-19 and didn’t detect any reaction between the patient’s naturally-derived antibodies and the syncytin-1 protein. Unfortunately I can’t find if that data was formally published in a medical journal, but I will leave the link to their editorial in the reference list for you to view if you choose.

Another claim is that the lipid nanoparticles (which is basically like the shuttle to get the fragile mRNA into the cells to do their recipe delivery work) accumulate in the ovary, and the second part of that claim is that this accumulation could affect their function. Before we begin this section, the word lipid means fat, and nanoparticle just means tiny particle, so lipid nanoparticle equals tiny fat particle. This claim has arisen from a couple of theoretical reasons, one being there is concern in general about nanoparticle exposure and potential accumulation in the ovary because they are present in many other things we are exposed to every day like makeup, processed food, and other health and personal care products including other medications. This is my very basic version interpretation, and I am not a biochemist, but lipid nanoparticles are made of fats like I said, and these are considered to be biodegradable. Your body is made up of around 25% fat, so it’s generally thought that your body knows what to do with the tiny fat particles that are in the mRNA vaccines.

So in the documentation provided to Japan’s medicinal regulation authorities, Pfizer outlines the process they went through to determine what happened to the nanoparticles and where they went. The way they did this was by injecting rats with lipid nanoparticles that had radioactive dye essentially mixed into them, then they could see how much of the dye was at different body parts and organs at 15 minutes after, 1 hour after, 2 hours, 4 hours, 8 hours, 24 hours and 48 hours and from that figure out the quantity of nanoparticles in each spot. So each rat was injected with 50micrograms of lipid nanoparticles like the ones that are used in the actual Pfizer vaccine. 50 micrograms is only one tenth of the dose given to humans, but the average Australian woman weighs 355x the weight of the average rat used in experiments, so the by-weight dosage human receive is significantly less.

So what did they find? They found that at 48hrs post injection, 24.6% of the radioactive dye and therefore the lipid nanoparticles were still at the injection site and 16.2% were at the liver. In males 0.074% of the dye was in the testes, and in females 0.095% was in the ovaries. I don’t have a measure as to what “toxic” levels are in each body part and 48hrs is as long as they monitored for. I’m thinking that’s how long the dye stays radioactive for, but I can’t give you any more information beyond what I’ve just stated, that a tiny amount did end up in the ovaries, but it’s far less than the 7% which is what I saw one online post claim.

And that’s pretty much all there is looking directly at fertility. As you can tell we need a LOT more research in this area, but early signs are promising that the short-term impact isn’t much. Obviously it’ll be a long time until we have long-term data on the effect of either COVID-19 or vaccination against it in relation to fertility.

It wouldn’t surprise me if there’s someone come up with stats around birth rates falling in countries with high vaccination rates soon, we’re getting to 9 months now since Israel did their roll out, so I’m kind of waiting for it. It’s unlikely we’ll be able to tease much info out from that because most developed nations have been experiencing a gradually declining birth rate for some time, and we generally see a dip in birth rates when there’s an economic downturn and job losses, which you are probably aware is right now. So I’ll be waiting for health research data rather than looking at vaccination rates and birth rates and trying to make any connection between those, but that’s just my thoughts. I digress.

We can’t talk about COVID-19, vaccination and fertility without talking about menstrual changes. Menstruation so important and so often overlooked in the world of research that still focuses largely on cis-gender men and expects people with female sex organs to just slot right in with their modeling.

There is a study from Wuhan itself, in China, published by Li and colleagues in September 2020. This study looked at the menstrual info of 177 women who had COVID-19. 25% of them reported menstrual volume changes (so heavier or lighter periods), 28% had menstrual cycle changes of some kind and 19% had a prolonged cycle duration. The average sex hormone profile in blood tests and AMH levels (which is kind of a proxy measure of how many follicles or eggs you have in your ovaries) were similar to age-matched controls. The authors conclude that “The menstruation changes of these patients might be the consequence of transient sex hormone changes caused by suppression of ovarian function that quickly resume after recovery.”

So it seems like menstrual changes are happening in a percentage of women who get COVID-19. Likewise, there are changes being reported by some women in the US and the UK regarding what seem to be temporary cycle changes after vaccination, and also in a minority of post-menopausal women and trans men who don’t usually bleed.

In the US, 1.67 million dollars has been granted across five universities to study the rate of menstrual changes and vaccination, and also tease out why it’s happening.

In the UK, 30 000 menstrual-change related reports have been made to their Medicines and Healthcare Products Regulatory Agency as well. Dr Victoria Male is a lecturer in reproductive immunology in the UK, and she wrote a piece for the British Medical Journal published on the 16th September 2021 about this. I’ll read a couple of paragraphs for you with translations as we go:

“Menstrual changes have been reported after both mRNA [so that’s Pfizer and Moderna] and adenovirus vectored covid-19 vaccines [like AstraZeneca is], suggesting that, if there is a connection, it is likely to be a result of the immune response to vaccination rather than a specific vaccine component. Vaccination against human papillomavirus (HPV) [so that’s the cervical cancer vaccine] has also been associated with menstrual changes. Indeed, the menstrual cycle can be affected by immune activation in response to various stimuli, including viral infection: in one study of menstruating women, around a quarter of those infected with SARS-CoV-2 experienced menstrual disruption [that’s the study from China I just mentioned before].

Biologically plausible mechanisms linking immune stimulation with menstrual changes include immunological influences on the hormones driving the menstrual cycle or effects mediated by immune cells in the lining of the uterus, which are involved in the cyclical build-up and breakdown of this tissue [side note that the lining of the uterus is maintained through other hormonal pathways in pregnancy, so this is unlikely to have any bearing on miscarriage rate, as I spoke about in the last video. I think she’s more suggesting that changes in bleeding symptoms might relate to when in the cycle the vaccination is administered.]. 

Research exploring a possible association between COVID-19 vaccines and menstrual changes may also help understand the mechanism.

Although reported changes to the menstrual cycle after vaccination are short lived, robust research into this possible adverse reaction remains critical to the overall success of the vaccination programme. Vaccine hesitancy among young women is largely driven by false claims that covid-19 vaccines could harm their chances of future pregnancy. Failing to thoroughly investigate reports of menstrual changes after vaccination is likely to fuel these fears. If a link between vaccination and menstrual changes is confirmed, this information will allow people to plan for potentially altered cycles. Clear and trusted information is particularly important for those who rely on being able to predict their menstrual cycles to either achieve or avoid pregnancy.” End quote.

So then comes the question: what should I do if I’m trying to conceive now, or I want to soon? And the annoying answer is, it’s totally up to you.

Talk with your doctors, talk with your partner, take the info around fertility, pregnancy and lactation research to date into account, keep abreast of more research as it comes to hand. I’d encourage you to think about your personal exposure risks, to tune out from everyone else’s emotional charge around this issue for a little while and do what you feel is best for you and your current and future little family.

I hope this was useful for you, again this is not instructive advice of any kind. I appreciate your interest in this topic and thank you for tuning in.





Articles cited:

Bowman, C. J., Bouressam, M., Campion, S. N., Cappon, G. D., Catlin, N. R., Cutler, M. W. et al. (2021). Lack of effects on female fertility and prenatal and postnatal offspring development in rats with BNT162b2, a mRNA-based COVID-19 vaccine. Reproductive Toxicology, 103, 28-35.

Gacci, M., Coppi, M., Baldi, E., Sebastianelli, A., Zaccaro, C., Morselli, S. (2021). Semen impairment and occurrence of SARS-CoV-2 virus in semen after recovery from COVID-19. Human Reproduction, 36(6), 1520-1529. 

Garg, I., Shekhar, R., Sheikh, A., & Pal, S. (2021). COVID-19 Vaccine in Pregnant and Lactating Women: A Review of Existing Evidence and Practice Guidelines. Infectious Disease Reports, 13(685-699). doi:10.3390/idr13030064

 Li, K., Chen, G., Hou, H., Liao, Q., Chen, J., Bai, H., et al. (2020). Analysis of sex hormones and menstruation in COVID-19 women of child-bearing age. Reproductive BioMedicine Online, 42(1), 260267.

Lu-Culligan, A., & Iwasaki, (2021, January 26). The False Rumors About Vaccines That Are Scaring Women. New York Times.

Male, V. (2021). Menstrual changes after covid-19 vaccination. British Medical Journal, 374:n2211. doi: 

Pfizer documents regarding rat nanoparticle study (page 16 and 17 of the pdf:

Safrai, M., Reubinoff, B., & Ben-Meir, A. (2021). BNT162b2 mRNA Covid-19 vaccine does not impair sperm parameters. MedRxiv. Advance Online Publication. doi:

 Safrai, M., Rottenstreich, A., Herzberg, S., Imbar, T., Reubinoff, B., & Ben-Meir, A. (2021). Stopping the misinformation: BNT162b2 COVID-19 vaccine has no negative effect on women’s fertility. MedRxiv. Advance Online Publication. doi:

Shimabukuro, T. T., Kim, S. Y., Myers, T. R., Moro, P. L., Oduvebo, T., Panagiotakopoulos, L. et. al. (2021). Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons. New England Journal of Medicine, 384, 2273-2282. DOI: 10.1056/NEJMoa2104983

 Zauche, L. H., Wallace, B., Smoots, A., Olson, C., Oduyebo, T., Kim, S. et al. (2021). Receipt of mRNA COVID-19 vaccines preconception and during pregnancy and risk of self-reported spontaneous abortions, CDC v-safe COVID-19 Vaccine Pregnancy Registry 2020-21. ResearchSquare. Advance Online Publication. Doi:12.21203/


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