Why Your Period Could Seem 'Off' After You Get the COVID Vaccine

Published on: Apr 26, 2021fb-roundtwitter-roundemail-round
Let's Talk About...COVID-19 Vaccines and Your PeriodGetty Images
The Story

A few of us at Skimm HQ have noticed that our periods seemed a bit ‘off’ after we got the COVID-19 vaccine. So we phoned fertility physician Dr. Natalie Crawford and asked her why that happens, what to know if you’re getting the COVID-19 vaccine and trying to get pregnant, and what’s actually considered an “irregular period.” Read Dr. Crawford’s answers to our Qs below. 

What information’s available about whether the COVID-19 vaccine changes your period? 

We don't yet have a study specifically looking at COVID-19 vaccines and abnormal bleeding — although we’re currently gathering data. Because the endometrium (Aka, the lining of the uterus) is an immune responsive tissue, it’s possible that when the body has a large immune response (i.e. making COVID-19 antibodies either from a COVID-19 infection or the COVID-19 vaccine), that it may make the endometrium unstable and cause changes in bleeding. We do know that 25% of women who had a COVID-19 infection reported a change in their period pattern (heavier or lighter, longer or shorter). This change lasted for 1-2 cycles and then returned to normal. The hypothetical reason was a stress or immune response (favoring an immune response). 

Does the COVID-19 vaccine impact a woman's ovulation window and ability (or timing) to conceive? 

Studies have shown that in women who’ve had either the COVID-19 infection or received the COVID-19 vaccine, there’s no change to ovarian function (ovulation and hormone production) or ovarian reserve (how many eggs you have). Hypothetically, a change in your bleeding pattern may make it harder to conceive in that particular cycle. However, the majority of people are not experiencing abnormal bleeding after the COVID-19 vaccine. We also have consistently good data showing that a COVID-19 infection during pregnancy can cause severe maternal and neonatal complications. So getting vaccinated before — or when — you’re pregnant is important. All professional societies who care for pregnant people or those trying to conceive recommend vaccination. The CDC now recommends vaccination after a large study (over 35,000 people) showed no increase in adverse events during pregnancy. 

What do women on fertility medication and/or planning an IUI procedure or IVF cycle need to know about how the COVID-19 vaccine may impact them?

If you’re undergoing fertility treatment, please talk to your doctor. We still recommend the vaccine, but not within three days of any fertility procedure (such as intrauterine insemination, egg retrieval, and embryo transfer). It’s common to cancel fertility procedures if you’re sick with any illness — even before the pandemic. The reason: your immune system may have a hard time responding appropriately for implantation (the process of a fertilized egg planting in the uterine lining) when it’s busy creating antibodies to your illness.

Does stress play a part in changing the timing or heaviness of a period?

Stress may play a role. Typically the body's response to a stressful situation is to shut off the brain's production of the hormones that allow you to ovulate (FSH and LH). This is called hypothalamic amenorrhea. When this happens, we see absence of periods for a prolonged period of time. This may explain why there are some reports of amenorrhea after a severe COVID-19 infection, but it’s unlikely after the COVID-19 vaccine because any reaction is very temporary and short-lived.

When should someone be concerned about an irregular period?

We define an “irregular period” as one that does not come at a regular and predictable interval. If you have a change in your period pattern for more than two cycles, you should see a doctor for an evaluation. Irregular periods can be caused by thyroid disease, pituitary dysfunction, PCOS, hypothalamic amenorrhea, chronic illness, and many other causes that require medical attention. Remember that your period is a "vital sign" and gives you information about your body.


There isn’t a completed study that addresses COVID-19 vaccines and abnormal bleeding yet. But here’s what we know: the endometrium (the lining of the uterus) is an immune responsive tissue. So it’s possible that when your body has a large immune response (i.e. making COVID-19 antibodies from the COVID-19 vaccine), that may make the endometrium unstable and cause temporary bleeding changes. Contact your doctor if your period doesn’t return to normal after two cycles.

This content is for informational and educational purposes only. It does not constitute a medical opinion, medical advice, or diagnosis or treatment of any particular condition. 

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Skimm'd by Carly Mallenbaum and Becky Murray

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