How a COVID-19 vaccine can (and cannot) affect menstruation, mammograms and more

As Canada ramps up its rollout of the COVID-19 vaccines, questions continue to arise aboutthe potential side effects reported around theworld.

Following reports of blood clots from theAstraZeneca-Oxfordand Johnson & Johnson vaccines, many women have wondered whether they are at higher riskespecially if they take hormonal birth control, which is also associated with clotting.

Experts saymore evidence is neededand that it's unclear whether women are at higher risk of developing blood clots than men.But four health experts told CBC News there arekey findingswomen cankeep in mind when getting the vaccine particularly ifthey are pregnant, booking a mammogram or a fertility treatment, or wondering whether it can disrupttheir menstrual cycle.

Here is what the experts said about how the COVID-19 vaccines can and cannot impact women'shealth.

Can the vaccine affect my period?

The question of whether a COVID-19 vaccinecould impact the menstrualcycle was prompted after an American professor of anthropology tweeted thatshe'd experienced an unusually heavy period after being immunized.

Her tweet prompted hundreds of other women to report that they too hadexperienced disruptions to their cycles from missed periodsto spottingto lighter or heavier bleeding than usual.

Neuroscientist Liisa Galea, a professor of psychology at the University of British Columbiaand ascientific adviser at the Women's Health Research Institute, said that while it's possible a vaccine could impact menstruation, it simply hasn't been studied enough to know for sure.

"One of the receptors through which SARS-CoV-2 enters our bodies is in the uterine lining.I'm wondering if maybe if you get the vaccine at the certain time in your cycle, you might notice some differences," she said.

Galeahas also heard anecdotal reports about women noticing changes in their period, but saidit's much more likely that the general stress of living through a global pandemic might be responsible for variations in menstruation that women are reporting.

"The important thing is it's not going to be long lasting. You might see a disruption or some spotting, a little hiccup, but as far as I can tell, there's no evidence that your cycle is going to change past that."

Jerilynn Prior, a professor of endocrinology at the University of British Columbia, agreedthat while the research is scarce, it'sunlikely that the vaccine would have such an immediate and tangible effect on the menstrual cycle.

"The variability of the menstrual cycle, even within one woman, is quite large in general," she said. Prior added that people who menstruate tend to be "hypervigilant" about their physiology after undergoing any medical procedure including receiving a vaccine.

Prior recommended that women track their periods and ovulation for a month before and after receiving the vaccine if they are interested in noting any changes.

Can the vaccine affect my mammogram results?

Experts say it's possible, but not a cause for concern.

Monika Naus, a medical director of the Communicable Diseases andImmunization Service at the BC Centre for Disease Control, said vaccinesof all kinds can cause swelling inthe lymph nodes located in the armpit on the side of the body where the injection takes place.

Because of their proximity to breast tissue, Naus saidswollen lymph nodes can sometimes appear as white blobs on a mammogram.

"There can be a false positive, and some concern that there's an abnormality there," she said.

Naus recommended that women wait four to six weeks after they've been vaccinated to go in for a routine mammogram though if they detect a breast lump or have concerns about their breast health, they should get screened immediately.

Prior said an experienced mammographer would likely be able to distinguish between a swollen lymph node and an abnormality in breast tissue, especially if they are warned ahead of time that a patient was recently vaccinated against COVID-19.

The CanadianAssociation of Radiologists and Canadian Society of Breast Imaging said a radiologist would also book a follow up to ensure any abnormalities can be attributed to the vaccine.

Can I get vaccinated if I'm pregnant or undergoing fertility treatments?

Although pregnant women were initially excluded from clinical trials, theCanadian Society of Obstetrics and Gynecology and the National Advisory Committee on Immunizationhave said the vaccine is considered safe for them.

Dr. Kathleen Ross, a family physician practising obstetrics at Royal Columbian Hospital in New Westminster, B.C., said it's especially important that pregnant women get the vaccine given that they are at higher risk of developing serious illness from COVID-19 should they fall ill.

"The vaccines are completely safe, they're not going to change your DNA,they're not going to cause any changes to the fetus. When a vaccine is offered to you, please, step up and get vaccinated," she said.

The COVID-19 vaccines have also been deemed safe for women undergoing fertility treatments. But theAmerican Society for Reproductive Medicine has recommended thatpatients scheduled for procedures like egg retrievalor intrauterine insemination avoid getting a COVID-19 vaccine within three days of a procedure.

The society says the recommendation is not because the vaccine is unsafe, but because the vaccine could induce side effects likefever, chills,and fatigue,which may be difficult to distinguish from a post-surgery infection.

The Canadian Fertility andAndrology Society recommends the same, writing the benefits of the vaccine far outweigh any known risks.

It suggests women discuss a treatment timeline with their doctors, given that Canadian provinces have extended the time framebetween the first and second doses of the vaccine.