COVID-19 vaccinations appear to have no impact on a couple’s ability to conceive a child, a new study says. 

The study, published Thursday in the American Journal of Epidemiology, found no major difference in conception rates between unvaccinated couples and vaccinated couples in which at least one partner had received at least one vaccine dose.

The researchers, however, did observe that couples with male partners who tested positive for COVID-19 within 60 days of a given menstrual cycle were 18% less likely to conceive.

The study was conducted by Amelia Wesselink, a reproductive and environmental epidemiologist at the Boston University School of Public Health, and her colleagues, and it was funded by the National Institutes of Health.

"This adds to the evidence from animal studies, studies of humans undergoing fertility treatment, and the COVID-19 vaccine trials, none of which found an association between COVID-19 vaccination and lower fertility," the scientists wrote in their paper. "Similarly, several studies have documented no appreciable association between COVID-19 vaccination and miscarriage risk."

Researchers analyzed data from a study of more than 2,100 American and Canadian couples who were trying to get pregnant without fertility treatment. Their findings were consistent even when taking into account factors such as whether participants had received one vaccine dose or two and the brand of vaccine they were given.

The scientists said a reason COVID-19 infection in men within 60 days of a cycle may have a short-term impact on conception is that fever, a common symptom of the virus, is known to reduce sperm count and motility. It could also be attributed to COVID-related inflammation in the testes and nearby tissue or erectile dysfunction. 

The study found no connection to COVID-19 infection in men and conception rates outside of the 60-day window. 

Surveys have found that reproductive-aged adults have cited concerns about potential effects of COVID-19 vaccines on fertility and pregnancies for not getting immunized.

The Boston University research follows another study published last week, out of Scotland, that found the rates of baby deaths and premature births were higher among mothers who were infected with the coronavirus 28 or fewer days before their delivery date. The researchers noted that the vaccination rate among pregnant women in Scotland is significantly lower than in the general population of women of similar age. Just 11% of pregnant women in the study who were infected with COVID-19 were fully vaccinated.