Adjustment of the spontaneous abortion rate following COVID-19 vaccination

Published:October 14, 2021DOI:https://doi.org/10.1016/j.ajogmf.2021.100511
      Our study included women who received at least one dose of an mRNA COVID-19 vaccine at any point during pregnancy, beginning at conception. We agree that selection bias is introduced by not accounting for the spontaneous abortion risk in the interim between conception and vaccination and by excluding those who had an early pregnancy loss in this time period. By excluding those who had an early pregnancy loss prior to vaccination, the spontaneous abortion rate was inherently lowered. To eliminate this bias, a cohort of pregnant women would need to be enrolled at conception and followed to determine the spontaneous abortion rate in those who elected to receive the vaccine compared to those who remained unvaccinated. This study design was not feasible at our center.
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