key: cord-0790553-waxa9p68
authors: TROSTLE, Megan E.; PENFIELD, Christina A.; ROMAN, Ashley S.
title: Adjustment of the spontaneous abortion rate following COVID-19 vaccination
date: 2021-10-14
journal: Am J Obstet Gynecol MFM
DOI: 10.1016/j.ajogmf.2021.100511
sha: 195827ef930ecbab4f2552e12ed155bc8551426a
doc_id: 790553
cord_uid: waxa9p68

nan

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. We thank Dr. Sun for his comments regarding our calculation of the rate of spontaneous abortion in women who received an mRNA COVID-19 vaccine during pregnancy. In our study, eight of the 124 women vaccinated in the first trimester had a spontaneous abortion yielding a rate of 6.5%.

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.

While statistical modeling can be used to approximate the true population estimate, its utility is limited in studies such as ours with a small sample size and low absolute number of spontaneous abortions. To reduce selection bias, we could limit our calculation of the spontaneous abortion rate to women who were vaccinated at early gestational ages. 1 Another strategy would be to limit the analysis to women who were vaccinated <8 weeks gestation (when spontaneous abortion risk is highest). In that case, our rate becomes 7/74 or 9.5%, which is similar to the rates reported by other studies on COVID-19 vaccination in pregnancy. 2 We agree the spontaneous abortion rate is dependent on the population and additional larger, multicenter studies that include a control group of unvaccinated women would better evaluate this risk. The recent study by Kharbanda et al 3 is better designed to assess the association between COVID-19 vaccination and spontaneous abortion. We recognize the limitations of our study in determining and reporting the risk of spontaneous abortion. We look forward to future studies which will provide further information on the impact of COVID-19 vaccination on pregnancy outcomes.

Selection Bias in Estimates of Early Pregnancy Loss

Receipt of mRNA COVID-19 vaccines preconception and during pregnancy and risk of self-reported spontaneous abortions, CDC v-safe COVID-19 Vaccine Pregnancy Registry 2020-21. Preprint. Res Sq. 2021;rs.3.rs-798175

Spontaneous Abortion Following COVID-19 Vaccination During Pregnancy