Covid-19 Vaccines and Miscarriage: What the Evidence Really Shows

False claims about Covid-19 vaccines and miscarriage are circulating online again, fueled by renewed debate over data collected during the early stages of the pandemic. One of the most widely repeated claims suggests that Covid-19 vaccination was associated with an 82% miscarriage rate. However, that figure comes from a flawed interpretation of an early vaccine safety study and does not represent the actual miscarriage risk among vaccinated pregnant women.

The issue has resurfaced following the release of text messages from Dr. Anthony Fauci's former government phone. Republican Sens. Ron Johnson of Wisconsin and Rand Paul of Kentucky released messages as part of their investigation into the federal government's handling of the Covid-19 pandemic. Some of the messages discussed theoretical questions about vaccine safety during pregnancy.

Those messages have since been used online to support claims that Covid-19 vaccines cause miscarriages. Medical experts say the interpretation is not supported by the broader body of scientific evidence.

Where the 82% Figure Came From

The controversy centers on a study published in the New England Journal of Medicine in April 2021. Researchers examined information from a vaccine safety monitoring system involving almost 4,000 women who received Covid-19 vaccines during the early months of the vaccine rollout.

Among those participants, researchers identified 827 pregnancies with known outcomes at the time of the initial analysis. There were 712 live births, 104 spontaneous abortions, commonly referred to as miscarriages, and 11 other outcomes.

Simply dividing 104 miscarriages by 827 completed pregnancies produces a figure of approximately 12.6%. Even that calculation required considerable caution because the study population and follow-up period had limitations.

A correction published later in 2021 made the situation clearer. Researchers explained that the available information did not allow them to calculate a reliable miscarriage rate from those numbers. Many participants had not been followed long enough for their pregnancy outcomes to be known, meaning the 827 completed pregnancies could not appropriately serve as the denominator for the entire group.

The researchers also pointed out an important statistical issue. About 700 of the completed pregnancies were already in their third trimester when vaccination occurred. Since most miscarriages happen earlier in pregnancy, those pregnancies could not simply be included or excluded without taking the timing of vaccination and pregnancy into account.

How the Data Became Distorted

Critics of Covid-19 vaccination have used the study's numbers in a different way. They exclude the approximately 700 third-trimester pregnancies and then calculate 104 miscarriages among the remaining 127 pregnancies.

That calculation produces a figure close to 82%.

The problem is that this number does not represent a miscarriage rate caused by vaccination. It uses a denominator that the researchers specifically said could not be used to calculate miscarriage risk.

This is a crucial distinction when interpreting medical research. A percentage can look alarming while still being statistically meaningless if the underlying population is selected incorrectly.

In this case, the 82% figure is not a finding from the study. It is the result of applying an inappropriate calculation to incomplete data.

What Larger Studies Have Found

The early study was never the final word on Covid-19 vaccination during pregnancy. Since 2021, researchers have accumulated substantially more information involving pregnant women who received Covid-19 vaccines.

According to the US Centers for Disease Control and Prevention, numerous studies have found no increased health risks for pregnant women or their babies associated with Covid-19 vaccination. The agency also says research indicates that vaccination during pregnancy can provide protection to both the mother and baby.

Medical organizations specializing in pregnancy and infectious diseases have similarly continued to support vaccination during pregnancy based on the available evidence.

Dr. Kevin Ault, an obstetrician and gynecologist, told CNN that the subject has been extensively studied and that a major increase in miscarriage risk would be extremely difficult to overlook after years of additional research.

Dr. Brenna Hughes of the Society for Maternal-Fetal Medicine has also emphasized that the benefits of vaccination outweigh the potential risks based on the accumulated scientific literature.

Covid-19 Infection Can Be Dangerous During Pregnancy

Another important part of the discussion is the risk posed by Covid-19 infection itself.

Pregnancy can increase the risk of serious complications from respiratory infections, and Covid-19 has been associated with severe illness, intensive care admissions and other adverse pregnancy outcomes.

Experts therefore stress that evaluating a vaccine during pregnancy requires comparing its potential risks with the risks of remaining unprotected against the disease.

According to specialists quoted by CNN, vaccination can reduce the risk of severe Covid-19 complications during pregnancy. The available evidence therefore does not support treating the vaccine as a greater threat to pregnancy than the infection itself.

Why Medical Data Need Context

The controversy illustrates how easily scientific statistics can be misunderstood or deliberately presented without context.

A study may contain a number that appears straightforward, but understanding what that number means requires examining how participants were selected, how long they were followed and whether the comparison group or denominator is appropriate.

That is especially important with pregnancy research. The probability of miscarriage changes throughout pregnancy, so researchers must consider the gestational age at vaccination and other factors when calculating risk.

Removing participants from a calculation simply because their pregnancies had progressed further can produce a dramatically different percentage without demonstrating that the underlying medical risk has changed.

For people trying to make decisions about vaccination during pregnancy, isolated statistics shared on social media can therefore be particularly misleading.

Where to Find Reliable Information

Pregnant people with questions about Covid-19 vaccination should discuss their individual circumstances with a qualified health professional. Medical societies and public health agencies can also provide information based on reviews of the broader scientific literature rather than a single disputed calculation.

The central point is straightforward: the claim that Covid-19 vaccines cause an 82% miscarriage rate is not an accurate interpretation of the evidence. The figure comes from manipulating the denominator of an early study in a way that the researchers themselves said was inappropriate for estimating miscarriage risk.

Years of additional research have provided a much larger evidence base. That broader literature has not shown that Covid-19 vaccination increases the risk of miscarriage.

Sources

• CNN, reporting on the disputed miscarriage claim and the interpretation of the 2021 vaccine safety study.
• New England Journal of Medicine, early safety monitoring study of Covid-19 vaccination during pregnancy.
• US Centers for Disease Control and Prevention, information and research on Covid-19 vaccination during pregnancy.
• Mayo Clinic, general information about miscarriage and its frequency.

Disclaimer

This article is for general informational and educational purposes only. It is a written summary based on the supplied source material and should not be considered medical advice, a diagnosis, or a recommendation for any individual. Health guidance can change as new evidence becomes available. Pregnant people should consult their doctor, midwife or other qualified healthcare professional for advice about vaccination and their personal circumstances.