Scientists study vaccine effects on fertility, pregnancy

Many women of child-bearing age who received a COVID-19 vaccine in recent months have reported menstrual changes, including irregular cycles and heavy bleeding. That unexpected side effect has fueled concerns about fertility and pregnancy: Could the COVID-19 shot harm an unborn child or affect a couple’s ability to conceive?

Several recent studies have suggested the vaccine does not endanger fertility or pregnancy. On the contrary, while COVID-19 infection does pose serious risks for pregnant women and the unborn, vaccination appears to protect them.

According to a population-wide study of pregnant women in Scotland published this month, vaccinated women who contracted COVID-19 while pregnant faced fewer risks of birth complications compared with the unvaccinated. Tracking every known pregnancy in Scotland between March 2020 and October 2021 (144,548 pregnancies in 130,875 women), researchers from the University of Edinburgh and Scotland’s public health agency found significant differences in birth outcomes for unvaccinated versus vaccinated women. Remarkably, all baby deaths associated with COVID-19 infection (including stillbirths and newborn deaths) occurred in unvaccinated women. Such women were four times more likely to deliver a stillborn baby than the general population. Vaccinated women had similar preterm birth rates (8.6) to the general population (8.0 percent), but the rate was almost twice as high in unvaccinated pregnant women (16.6 percent), according to the study, published in Nature.

“The conclusion is that, unfortunately, COVID has significant impacts on maternal health and pregnancy outcomes,” said Jennifer Hadlock, an assistant professor at the Institute for Systems Biology (ISB) in Seattle. She pointed out that the Scotland study was the first showing that vaccination is associated with reduced risks for mothers and babies.

Hadlock’s organization performed its own study of maternal COVID-19 and pregnancy risk, a retrospective analysis using electronic health records from nearly 74,000 unvaccinated pregnant women. Her team’s study, published this month in The Lancet Digital Health, examined pregnant women with mild or moderate cases of COVID-19 and showed similarly poor birth outcomes for unvaccinated pregnant women, including increased risk for preterm delivery and stillbirth.

The Scotland study’s authors noted they did not control for confounding variables that could explain the findings. The ISB study did control for factors associated with poor birth outcomes, including maternal age, ethnicity, comorbidities, and socioeconomic factors. Surprisingly, preterm birth and stillbirth in the ISB study didn’t correlate with COVID-19 infection severity. “Even mild COVID infections resulted in increased risk for adverse outcomes,” said Hadlock. (Previous studies have shown that pregnant women are not more susceptible to getting COVID-19 but are more likely to have a severe infection.)

Another study, published in the American Journal of Epidemiology, addresses concerns about COVID-19 vaccination’s effect on fertility. Researchers analyzed data from over 2,000 U.S. and Canadian couples enrolled in the Pregnancy Study Online (PRESTO), a questionnaire-based survey designed to track how clinical and lifestyle factors affect fertility and pregnancy. The study authors, led by Amelia Wesselink at Boston University, found no significant difference in the chances of conception between couples who reported vaccination of one or both partners compared to unvaccinated participants. Testing positive for COVID-19 was not associated with a decreased likelihood of conception overall, but for couples in which the male partner tested positive within 60 days of a given menstrual cycle, chances of conception dropped by 18 percent. “[COVID-19 virus] infection among male partners was associated with a short-term decline in fertility that may be avoidable by vaccination,” noted the study authors.

A study published in Obstetrics & Gynecology examined vaccines and the menstruation problem. It found that COVID-19 vaccination was associated with a slightly longer cycle (less than one day longer on average, but up to eight days longer in some cases), but no change in menses length. The increased cycle length was temporary. “On a population level, the changes we are finding indicate no cause for concern for long-term physical or reproductive health,” lead author Alison Edelman of Oregon Health and Science University said in a statement.

In the United States, Pfizer and Moderna excluded pregnant women from their initial COVID-19 vaccine trials because the vaccines’ effect on unborn children was unknown. Some bioethicists argue pregnant women should have been included.

Dr. Jeffrey Barrows, a retired OB-GYN and senior vice president of bioethics and public policy at the Christian Medical and Dental Associations, recommends a nuanced approach. He agrees with Pfizer and Moderna’s decision to exclude pregnant women from initial trials, but given COVID-19’s known harm for pregnant women, he said, “Not only is it ethical, at some point in time, it becomes imperative to study the safety of a proven vaccine in pregnant women.”