COVID-19 mRNA vaccination during pregnancy does not harm syncytiotrophoblast development

OBJECTIVES: The safety of COVID-19 messenger RNA (mRNA) vaccination during pregnancy remains a topic of concern. Its effect on placenta development has been poorly studied, even though this is essential for healthy pregnancy outcomes. We investigated the effect of the maternal immune response to COVID-19 mRNA vaccination on the development of syncytiotrophoblast (STB), a functional cell layer of the placenta where the maternal-fetal exchange takes place.

METHODS: We collected sera from pregnant women before vaccination and after the second vaccination with the Pfizer-BioNTech mRNA vaccine (n=12 paired samples). Human trophoblast stem cells were subjected to in vitro STB differentiation in the presence of the serum samples. Cell morphology, proliferation, and marker gene expression were assessed to determine STB differentiation.

RESULTS: All cells obtained an STB-like morphology, upregulated STB markers, and downregulated trophoblast stem cell markers. We did not find any significant differences in the extent of differentiation between STBs treated with pre- and post-vaccination serum samples.

CONCLUSION: This in vitro study suggests that the maternal inflammatory response and the presence of SARS-CoV-2 antibodies in the maternal blood are not harmful to STB development of the placenta. These findings support the growing body of evidence that COVID-19 mRNA vaccination during pregnancy is safe.