The Centers for Disease Control and Prevention (CDC) researchers, who conducted the study, noticed that there was a large number of women who miscarried within 28 days of getting a flu shot with protection from swine flu, but only if they had also received the flu shot in the previous season as well.
However, the authors think it's too early to change the government recommendation that all pregnant women be vaccinated against the flu.
"This study does not and cannot establish a causal relationship between repeated influenza vaccination and SAB (spontaneous abortion), but further research is warranted," wrote the authors of the article.
Possible limitations of the study include that the sample size was too small and that women with increased risk of miscarriage were the ones receiving vaccinations in the first place.
"I want the CDC and researchers to continue to investigate this," Dr. Laura Riley, a Boston-based obstetrician, said. "But as an advocate for pregnant women, what I hope doesn't happen is that people panic and stop getting vaccinated."
The CDC has already proactively reached out to a doctor's group, the American Congress of Obstetricians and Gynecologists, to let them know that they can expect to gets lots of appointments from worried moms-to-be.
On the CDC website, the organization has already stated that there is a "potential safety signal associated with flu vaccination of pregnant women."
According to the CDC website, "This study does not quantify the risk of miscarriage and does not prove that flu vaccine was the cause of the miscarriage. Earlier studies have not found a link between flu vaccination and miscarriage. There is an ongoing investigation to study this issue further."
The website goes on to say, "CDC and its Advisory Committee on Immunization Practices (ACIP) are aware of these data, which were first presented to ACIP at a public meeting in June 2015. At this time, CDC and ACIP have not changed the recommendation for influenza vaccination of pregnant women."
The CDC still recommends that pregnant women get a flu vaccine at any point during a pregnancy because influenza always poses a danger to pregnant women and the vaccine can still prevent the illness effectively.