(CNN) -- A new study adds to growing evidence that there is no connection between Covid-19 vaccinations and a reduced chance of conceiving.
Rather, couples in the study had slightly lower chances of conception if the male partner had been infected with the coronavirus within 60 days -- which offers even more reason to get vaccinated against Covid-19, since the illness could affect male fertility in the short term, according to the study, published Thursday in the American Journal of Epidemiology.
"These findings indicate that male SARS-CoV-2 infection may be associated with a short-term decline in fertility and that COVID-19 vaccination does not impair fertility in either partner," Amelia Wesselink and her fellow researchers -- from the Boston University School of Public Health and other institutions across the United States -- wrote in the study. SARS-CoV-2 is the name of the virus that causes Covid-19.
"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 researchers wrote. "Similarly, several studies have documented no appreciable association between COVID-19 vaccination and miscarriage risk."
The study included data on 2,126 women, ages 21 to 45, in the United States and Canada. The women enrolled in the study from December 2020 through September 2021, and the researchers followed up with them through November 2021.
During the study, the women completed questionnaires online every eight weeks about their reproductive and medical histories, among other factors, and they were given the option to invite their male partners to complete questionnaires. Among the participants, 73% of the women and 74% of their male partners had received at least one dose of Covid-19 vaccine.
The researchers analyzed the questionnaire responses and found no association between having been vaccinated against Covid-19 and the probability of conceiving a child within one menstrual cycle. Yet the data showed that although a previous Covid-19 infection was not strongly associated with the probability of conceiving among the women, the men who had Covid-19 were associated with a "transient reduction" in the probability of conceiving.
The National Institutes of Health announced the study findings in a news release Thursday and noted that couples in which the male partner had tested positive within 60 days were 18% less likely to conceive in that menstrual cycle, but there was no difference in conception rates for couples in which the male partner had tested positive more than 60 days before a cycle, compared with couples in which the male partner had not tested positive.
More research is needed to determine what might be driving these findings, but fever is known to reduce sperm count and is a symptom of Covid-19, according to the NIH.
"The findings provide reassurance that vaccination for couples seeking pregnancy does not appear to impair fertility," Dr. Diana Bianchi, director of the NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, which funded the study, said in the announcement. "They also provide information for physicians who counsel patients hoping to conceive."
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