Results of this prospective cohort study fits with other evidence showing no association between COVID-19 vaccination and miscarriage.
COVID-19 vaccination before conception, whether received by a male or female partner, does not lead to a higher miscarriage rate, according to a study published late last month in Human Reproduction. The analysis was conducted among 1,815 female participants who conceived between December 2020 and November 2022, including 1,570 couples who provided data on male partner vaccination.
Illness from COVID-19 poses a greater risk to pregnant individuals, but COVID-19 vaccines have been shown to effectively reduce the severity of the virus. There is no clear evidence that COVID-19 vaccines cause miscarriage, yet vaccine-hesitant individuals of reproductive age continue to report concerns about safety related to pregnancy and fertility.
Several observational studies have shown that there is no increased risk of miscarriage following COVID-19 vaccination. However, none of these studies have specifically focused on the effects of male partner vaccination on miscarriage.
A group of researchers, including first author Jennifer J. Yland, Ph.D., then at the Boston University School of Public Health, have conducted a prospective cohort study to examine the association between preconception COVID-19 vaccination and miscarriage.
The Pregnancy Study Online (PRESTO) is a research study that began in 2013 and is still ongoing. It involves couples in the USA and Canada who are trying to conceive without fertility treatment. Participants complete questionnaires at various intervals and are given home pregnancy tests.
In the new cohort study, participants reported information on pregnancy outcomes, including miscarriages, and provided details on their pregnancies. Miscarriages were categorized as early (before week 8 of gestation) or late (weeks 8–19 of gestation). Information on COVID-19 vaccination and infection was also collected. Vaccines received during pregnancy were not included in the exposure definition.
The study found that almost one-quarter of pregnancies resulted in miscarriage, with 75% of those miscarriages occurring before 8 weeks gestation. Additionally, 75% of eligible female participants had received at least one dose of a COVID-19 vaccine before the time of conception.
Statistical analysis showed an incidence rate ratio (IRR) comparing female participants who received at least one dose of the vaccine before conception versus those who had not been vaccinated was 0.85 (95% CI: 0.63, 1.14). This suggests that there was no significant difference in the risk of miscarriage between vaccinated and unvaccinated women.
Furthermore, the analysis found no indication of an increased risk of either early miscarriage or late miscarriage associated with COVID-19 vaccination. The IRR for male partner vaccination, comparing the risk of miscarriage between those with vaccinated partners and those without, was 0.90 (95% CI: 0.56, 1.44). This suggests that there was no significant association between male partner vaccination and the risk of miscarriage.
Overall, these results suggest that COVID-19 vaccination, whether received by the female participant or their male partner, was not associated with an increased risk of miscarriage.
A limitation of the study is the self-reported information on vaccination and infection history that may be inaccurate. However, the study design and use of home pregnancy testing helped minimize the chances of missing any miscarriages. Also,as with any observational study, there is a possibility of unaccounted factors influencing the results.
But this is among the first, it not the first, prospective study that involving enrolling volunteers before conception and the following up regularly to examine the connection between COVID-19 vaccination before pregnancy and miscarriage. The study included a wide range of gestational ages at loss (4-19 weeks) and a high percentage of early losses (less than 8 weeks: 75%).
The results showed that vaccination did not have any harmful effects on miscarriage. In fact, the rate of miscarriage among vaccinated individuals was similar to that of participants who conceived before the COVID-19 pandemic.
The study was supported by several funding sources, including the National Institute of Child Health and Human Development, the National Institute of Health, the National Institute of Allergy and Infectious Diseases, and the National Science Foundation.