Withdrawn paper related to the risk of miscarriage in pregnancy after covid-19 vaccination

Simon Thornley, Aleisha R. Brock.


Re: Brock AR and S Thornley. 2021. Rapid Communication Spontaneous Abortions and Policies on COVID-19 mRNA Vaccine Use During Pregnancy. Science, Public Health Policy & the Law 4:130-143.


As the authors of the above paper, we have asked the publisher to withdraw it. This is because it has the alarming statistic “Our re-analysis indicates a cumulative incidence of spontaneous abortion 7 to 8 times higher than the original authors’ results (p < 0.001) and the typical average for pregnancy loss during this time period”. This calculation is not justified and does not represent the true risk of miscarriage given exposure to the vaccine in early pregnancy.

In our re-analysis, a calculation was made from an ambiguous description of the methods of the original article1 and as such the true incidence of spontaneous abortions in those exposed to mRNA vaccines prior to 20 weeks’ gestation could not be accurately estimated. This occurred due to a short study duration (11-weeks) and no active follow-up in these groups by the conclusion of the study. This resulted in an overestimated calculation of 82-91% or 7-8 fold increase in spontaneous abortions. This overlooked the 1,132 women exposed in the first trimester, who would not have registered a completed pregnancy by the end of the study. Of the 104 miscarriages, 96 occurred in the first trimester and 8 in the second trimester. This means the miscarriage cumulative incidence was 104/1,132 or 9.2%.

A follow-up publication based on the same cohort quotes a cumulative incidence of miscarriage of 14.1%.2 This is considerably lower than the 7 to 8 fold increase that we calculated. There are a range of background miscarriage rates quoted in comparable studies before the covid-19 era which range from 5.4%3 to 21.3%.4 Of note, another case-control study from Norway shows no increased risk in exposure to covid-19 vaccination, comparing women with a first trimester miscarriage to those with a first trimester pregnancy.5

From this evidence, we withdraw the recommendation that covid mRNA injections be considered ‘category X’, but rather suggest caution with their use, in consideration of the overall risks of covid-19 infection in pregnancy.6 We unreservedly apologise for any alarm caused by the publication of the paper.


1. Shimabukuro TT, Kim SY, Myers TR, et al. Preliminary findings of mRNA Covid-19 vaccine safety in pregnant persons. New England Journal of Medicine 2021;384(24):2273-82.

2. Zauche LH, Wallace B, Smoots AN, et al. Receipt of mRNA Covid-19 vaccines and risk of spontaneous abortion. New England Journal of Medicine 2021;385(16):1533-35.

3. Naert MN, Khadraoui H, Muniz Rodriguez A, et al. Stratified risk of pregnancy loss for women with a viable singleton pregnancy in the first trimester. The Journal of Maternal-Fetal & Neonatal Medicine 2020:1-7.

4. Mukherjee S, Velez Edwards DR, Baird DD, et al. Risk of miscarriage among black women and white women in a US Prospective Cohort Study. American Journal of Epidemiology 2013;177(11):1271-78.

5. Kharbanda EO, Haapala J, DeSilva M, et al. Spontaneous Abortion Following COVID-19 Vaccination During Pregnancy. Journal of the American Medical Association 2021;326(16):1629-31. doi: 10.1001/jama.2021.15494

6. Son M, Gallagher K, Lo JY, et al. Coronavirus Disease 2019 (COVID-19) Pandemic and Pregnancy Outcomes in a U.S. Population. Obstetrics and Gynecology 2021;138(4):542-51. doi: 10.1097/AOG.0000000000004547