key: cord-1038213-alpj0ts7
authors: Sun, Hong
title: Approximation and evaluation of the spontaneous abortion rate with COVID-19 vaccination in pregnancy
date: 2021-10-14
journal: Am J Obstet Gynecol MFM
DOI: 10.1016/j.ajogmf.2021.100510
sha: 671aa23015fab53ec086831355c6c0d6956fc49a
doc_id: 1038213
cord_uid: alpj0ts7

nan

In the commented paper, the spontaneous abortion rate in the first trimester (6.4%) is calculated by dividing the eight spontaneous abortions by the 124 pregnant women who received vaccination in their first trimester 1 . When a pregnant woman received the COVID-19 vaccine, the risk of spontaneous abortion during the period of the start of pregnancy and the week of gestation that the vaccine was received is excluded. If an abortion happened during this period, the pregnant woman was automatically excluded in this study, which brings a selection bias. Adjustment is therefore required to faithfully reflect the actual risk of spontaneous abortion with the COVID-19

vaccine in pregnancy 2 . Based on the details of the available data, different levels of approximation can be made.

When the week of gestation that the vaccine is received is unknown, a rough estimation can be made by assuming the week of gestation at the vaccination were equally distributed. Based on the spontaneous rate of each week of gestation reported in the literature, it is possible to make a very rough estimation for adjustment 2 . When the week of gestation that the vaccine is received is available, it is then possible to make a more accurate approximation by calculating the risk of spontaneous abortion for each gestational week and generating a cumulative risk 3 . In the reported study 3 , the unadjusted risk of spontaneous abortion in the first trimester is 11%, the cumulative risk of spontaneous abortion in the first trimester is calculated as 13.61%.

The spontaneous abortion rate is highly dependent on the population group under investigation, it is therefore hard to evaluate the impact of the COVID-19 vaccine on the risk of spontaneous abortion in a single institution. More reliable evaluation can be performed by constructing a reference group that contains pregnant women who did not receive the COVID-19 vaccine, by recruiting them to the reference group at the same gestation week as their counterpart in the case group. It would be possible to evaluate the impact of COVID-19 vaccine on spontaneous abortion, as well as other relevant outcomes, by comparing these two groups 4 .

COVID-19 vaccination in pregnancy: early experience from a single institution

Adjustment is Required to Calculate the Risk of Early Pregnancy Loss with Covid-19 Infection or Vaccination

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

Association between BNT162b2 vaccination and incidence of SARS-CoV-2 infection in pregnant women