Evidence mRNA COVID-19 Vaccines are Safe During Pregnancy

A Northwestern University Medicine study of placentas from women who received a COVID-19 vaccine during pregnancy found no evidence of injury.

Most women in this limited study received either Moderna or Pfizer-BioNTech mRNA vaccines during their third trimester.

The study was published May 11, 2021, in the journal Obstetrics & Gynecology. To the authors’ knowledge, it is the first study to examine the impact of the COVID vaccines on the placenta.

The study authors collected placentas from 84 vaccinated patients and 116 unvaccinated patients who delivered at Prentice Women’s Hospital in Chicago, Illinois, and pathologically examined the whole of the placenta and microscopically following the birth.

The placenta is the first organ that forms during pregnancy. It performs duties for most of the fetus’ organs while they’re still forming, such as providing oxygen while the lungs develop and nutrition while the gut is forming. 

Additionally, the placenta manages hormones and the immune system and tells the mother’s body to welcome and nurture the fetus rather than reject it as a foreign intruder. 

The scientists also looked for abnormal blood flow between the mother and fetus and problems with fetal blood flow – both of which have been reported in pregnant patients who have tested positive for COVID.  

The rate of these injuries was the same in the vaccinated patients as for control patients.

The Northwestern scientists also examined the placentas for chronic histiocytic intervillositis, a complication that can happen if the placenta is infected, in this case, by SARS-CoV-2. 

Although this study did not find any cases in vaccinated patients, it's a rare condition requiring a larger sample size (1,000 patients) to differentiate between vaccinated and unvaccinated patients.

The study was funded by The Friends of Prentice, the Stanley Manne Children’s Research Institute, the National Institute of Biomedical Imaging and Bioengineering, and the National Institute of Allergy and Infectious Diseases.