COVID Paper Database
Study Summaries
Spontaneous Abortion Follow in COVID-19 Vaccination During Pregnancy
Reviewed by Charles Li, MD
April 21, 2023
Summary
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Question- Does COVID-19 vaccination cause spontaneous abortion?
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Method - 105,446 pregnancies were analyzed in a case-control study.
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Result - No link was found between spontaneous abortion & vaccination.
Researchers ran a case-control study to see whether COVID-19 vaccination is associated with spontaneous abortion. They studied 105,446 pregnancies, including 13,160 cases of spontaneous abortion. They found that there was no significant difference between the exposure group and the control group. They concluded that COVID-19 vaccination is not associated with a higher rate of spontaneous abortion.
Background
There are currently two vaccines authorized for pregnant women in the United States. Before this study, data on COVID-19 vaccine safety in pregnant women has come mostly from passive observation. Passive observation studies can be useful but they are not as powerful as controlled studies.
This study compared women who experienced spontaneous abortion and women who had ongoing pregnancies to look for any link between vaccination and pregnancy outcomes.
Study Quote
COVID-19 infection during pregnancy can be associated with severe maternal morbidity. In the United States, 1 COVID-19 vaccine has been approved and 2 have been authorized for use for pregnant women. To date, data on maternal COVID-19 vaccine safety come primarily from passive surveillan...
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Methods
To look for links in the data, researchers grouped women into two groups: those who experienced a spontaneous abortion and women who had healthy ongoing pregnancies.
They then looked at vaccination data to see if women who experienced spontaneous abortion were more likely to have had a COVID-19 vaccination within 28 days than similar women with ongoing pregnancies.
The study covered 105,446 pregnancies and 13,160 cases of spontaneous abortion.
Study Quote
We analyzed the odds of receiving a COVID-19 vaccine in the 28 days prior to spontaneous abortion compared with the odds of receiving a COVID-19 vaccine in the 28 days prior to index dates for ongoing pregnancies. ... Of 105 446 unique pregnancies, 13 160 spontaneous abortions and 92 286 ongoing pregnancies were identified...
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Results
Study Quote
Spontaneous abortions did not have an increased odds of exposure to a COVID-19 vaccination in the prior 28 days compared with ongoing pregnancies (adjusted odds ratio, 1.02; 95% CI, 0.96-1.08).
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Researchers found that vaccination rates between the groups were essentially the same.
There was no statistical difference between the control and exposure groups. Women who had experienced spontaneous abortion were just as likely to have been vaccinated as women with ongoing pregnancies.
Of note, the 0.6% difference shown below is well within the margin-of-error of the study.
A case-control study found that women who experienced spontaneous abortion were not more likely to have been vaccinated compared to similarly matched women who had ongoing pregnancies.
Key Figure: Table 2
COVID-19 Pregnancy Safety Data
Rates of spontaneous abortion were equivalent among the Pfizer and Moderna vaccines. Rates were also approximately equal between different weeks of pregnancy.
When broken down by gestational week (aka pregnancy week), researchers found no significant differences between groups. Later pregnancies had a higher rate of spontaneous abortion, but this difference was statistically insignificant (e.g. within the margin of error).
Discussion
Study Quote
Among women with spontaneous abortions, the odds of COVID-19 vaccine exposure were not increased in the prior 28 days compared with women with ongoing pregnancies. ..
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Based on these data, researchers concluded that there was no significant link between COVID-19 vaccination and spontaneous abortion. Women who get vaccinated during pregnancy are not more likely to experience spontaneous abortion.
The study's strengths include its size and diversity. A study that covers more locations may be more applicable to the general population than a study that's performed in a single hospital.
However, the authors did note that they may have missed certain vaccination events, or may have collected inaccurate vaccination statuses since this study was conducted during vaccine rollout.
The authors do however believe that this data is reliable for future vaccination recommendations and for discussing vaccinations for pregnant women.