The mRNA Covid-19 vaccines made by Pfizer/BioNTech and Moderna do not appear to pose any serious risk during pregnancy, according to new data published Wednesday in the New England Journal of Medicine.
Pregnant women with Covid-19 are at increased risk for severe illness and may be at increased risk for adverse outcomes, such as preterm birth, according to the US Centers for Disease Control and Prevention. The study, along with existing research showing mRNA vaccines are effective in pregnant and lactating women, suggests that the benefits of the vaccines outweigh the risks.
The new study reviewed data on 35,691 pregnant people between December 14, 2020 to February 28, 2021 from the CDC's V-safe smartphone-based surveillance system, as well as data from the CDC's Vaccine Adverse Event Reporting System (VAERS). All participants were pregnant and 16 to 54 years old.
The researchers followed a group within the V-safe system to gather more data on pregnancy outcomes and complications. This registry included 3,958 pregnant participants (out of the 35,691) who had received an mRNA vaccine. They found 827 completed pregnancies, and 115 (13.9%) experienced a pregnancy loss, while 712 (86.1%) resulted in a live birth. Preterm births occurred in 9.4% of participants and only 3.2% of these births were small gestational age. There were no neonatal deaths reported.
There were 221 pregnancy-related adverse events reported to the CDC's VAERS registry, and 46 of them were miscarriages.
"Although not directly comparable, calculated proportions of adverse pregnancy and neonatal outcomes in persons vaccinated against Covid-19 who had a completed pregnancy were similar to incidences reported in studies involving pregnant women that were conducted before the Covid-19 pandemic."
The study also looked at vaccine side effects during pregnancy. Researchers found the most common side effect from the vaccine was pain at the injection site, which appeared to occur more frequently in vaccine recipients who were pregnant. However, headache, muscle aches, chills and fever were reported less frequently by pregnant people.
The researchers say more long-term studies are needed to assess the safety of the Covid-19 vaccine during pregnancy, and that this research should include follow up with a large population who are vaccinated early in pregnancy.
"Continued monitoring is needed to further assess maternal, pregnancy, neonatal, and childhood outcomes associated with maternal Covid-19 vaccination, including in earlier stages of pregnancy and during the preconception period," the researchers wrote. "Meanwhile, the present data can help inform decision making about vaccination by pregnant persons and their health care providers."