Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons.
Level 3 - non-randomized controlled study
Prospective observational surveillance and registry cohort study without a concurrent unvaccinated control group
PubMed 33882218 · doi:10.1056/NEJMoa2104983
What was done
Data from three US CDC surveillance systems (the v-safe smartphone surveillance system, the v-safe pregnancy registry, and the Vaccine Adverse Event Reporting System [VAERS]) were analyzed between December 14, 2020, and February 28, 2021, to assess early safety outcomes of mRNA Covid-19 vaccines in pregnant individuals aged 16 to 54 years.
What was found
Among 35,691 pregnant v-safe participants, injection-site pain was reported more frequently than in nonpregnant individuals, while headache, myalgia, chills, and fever occurred less frequently. Among 3,958 participants enrolled in the pregnancy registry, 827 had completed pregnancies: 712 (86.1%) resulted in live births (primarily vaccinated in the third trimester) and 115 (13.9%) resulted in pregnancy loss. Neonatal outcomes included preterm birth in 9.4% and small size for gestational age in 3.2%, with zero neonatal deaths. These rates were comparable to pre-pandemic baseline estimates. In VAERS, 221 pregnancy-related adverse events were reported, the most frequent being spontaneous abortion (46 cases).
Why it matters
These initial surveillance data provided early reassurance regarding the safety profile of mRNA Covid-19 vaccines during pregnancy, showing no overt signals of increased pregnancy or neonatal complications.
Limits
The findings are preliminary and rely on voluntary reporting systems and registries without concurrent, randomized unvaccinated controls. The completed pregnancy cohort primarily reflected third-trimester vaccination, leaving outcomes following first- and early second-trimester vaccination largely unassessed at the time of analysis.
Cited by
- supports A New England Journal of Medicine study using v-safe registry data found no statistically significant difference in rates of adverse pregnancy outcomes—including pregnancy loss, preterm birth, and congenital abnormalities—between vaccinated pregnant persons and published baseline population rates.