A recent study from the Czech Republic has made headlines by asking a bold (but recurring) question: Are women who get the COVID-19 vaccine less likely to become pregnant? The researchers behind the study analyzed data from over a million women between the ages of 18 and 39. They compared the rates of successful conceptions (pregnancies that resulted in live births) among those who had been vaccinated before conceiving.
The results showed something unexpected. Starting in mid-2021, conception rates were lower among women who had received a COVID-19 vaccine before getting pregnant. This was true even though approximately 70 percent of women in this age group had been vaccinated. When researchers compared birth rates between vaccinated and unvaccinated women, the difference stood out.
Now, that might sound alarming. However, before jumping to conclusions (like some anti-vaccine activists have), it’s essential to examine the study’s methodology and its limitations.
The researchers utilized national data, a significant strength. Instead of relying on small groups of volunteers, they had access to information from nearly every woman in the country within the age range. That makes the results more reliable in terms of population trends. Another strong point is that they measured a clear and simple outcome: live births. That’s not something people are likely to forget or misreport, so the data is likely accurate.
But here’s the catch: the study didn’t track individual women or ask them personal questions about their health, their efforts to get pregnant, or their medical history. It looked at groups of people based on their vaccination status and birth outcomes. This is what scientists call an “ecological” study, and while it can show big-picture patterns, it cannot prove cause and effect.
To help understand the limits of this approach, think of it like looking at a neighborhood where houses with blue doors have fewer holiday decorations than houses with red doors. You might guess that blue door owners don’t celebrate as much, but perhaps they’re just more likely to decorate their homes inside, or maybe they travel during the holidays, or the color scheme for holiday decorations doesn’t go well with blue doors. You can’t know why without asking them directly. Similarly, this Czech study can reveal an association, but not the underlying reasons.
There are several possible explanations for why vaccinated women had lower conception rates. For example, women who planned to get pregnant might have chosen to delay vaccination or skip it entirely out of caution. On the other hand, some women may have gotten vaccinated and then decided to wait before trying to conceive. The study didn’t collect this kind of personal information, so we don’t know what individual decisions or health situations looked like.
Another factor is that COVID-19 and the stress of the pandemic disrupted many people’s lives. Some may have put off having children due to job insecurity, health concerns, or loss of childcare. If vaccinated women were more likely to work in healthcare or education, they might have delayed pregnancy more than others, not because of the vaccine, but due to life circumstances.
The researchers themselves are careful to point out that their findings do not prove harm. They describe the results as “hypothesis-generating,” which means they raise questions for future research but do not provide solid answers. And this is where public health comes in.
Other studies, especially those that follow individuals over time, have not shown a link between COVID-19 vaccines and reduced fertility. In fact, many professional organizations, like the CDC and the American College of Obstetricians and Gynecologists, continue to support vaccination during reproductive years and even during pregnancy. These recommendations are based on a growing body of evidence from high-quality studies that account for personal health factors and the timing of conception.
So, what does this study really tell us? It suggests that we require more detailed research. It indicates that tracking national trends is useful, but not sufficient. And it reminds us how important it is to ask the right kinds of questions when it comes to health, especially with something as sensitive and personal as fertility.
If you’re someone thinking about starting a family, and you're unsure about getting vaccinated, the best step is to talk to your doctor. They can explain what the latest science says, help you think through your options, and support your choices. It may seem quick and easy to ask strangers on the internet, but it may lead you to believe that an ecological study is the definitive word on a subject.
Public health recommendations aim to protect individuals and communities, but they should always be grounded in transparent, high-quality evidence. This study adds an interesting piece to the puzzle, but it doesn’t solve it.
In the end, science is a conversation. This study from the Czech Republic has given us something to talk about, and now it’s up to researchers, healthcare providers, and the public to keep that conversation going with care, curiosity, and respect.
Here is the full study citation for you to read the paper yourself:
Manniche, V., Fürst, T., Schmeling, M., Gilthorpe, J. D., & Hansen, P. R. (2025). Rates of successful conceptions according to COVID-19 vaccination status: Data from the Czech Republic. International Journal of Risk & Safety in Medicine.