During the study period, there were approximately 1,300,000 women aged 18–39 years in the Czech Republic, and the proportion of COVID-19-vaccinated women increased from January 2021 until reaching a steady state of around 70% by the end of 2021.

At least from June 2021, successful conceptions per 1000 women were considerably lower for women who were vaccinated, compared to those that were unvaccinated, before SC.

Furthermore, successful conception rates for the vaccinated group were much lower than expected based on their proportion of the total population.

In the Czech Republic, successful conception rates were substantially lower for women vaccinated against COVID-19 before successful conception than for those who were not vaccinated. These hypothesis-generating and preliminary results call for further studies of the potential influence of COVID-19 vaccination on human fecundability and fertility.