A spike in foetal loss after Covid-19 vaccination in early pregnancy

A new analysis has raised serious concerns about the safety of Covid-19 vaccination in early pregnancy.

Women who received an mRNA vaccine between 8 and 13 weeks gestation experienced a significantly higher rate of foetal loss—around 13 losses per 100 pregnancies—compared to an expected rate of just 9.

Published as a preprint by Guetzkow et al., the study analysed more than 220,000 pregnancies between 2016 and 2022 in Israel.

Among the authors are Retsef Levi, newly appointed to the CDC’s vaccine advisory panel, and Tracy Beth Høeg, now a senior advisor for clinical sciences at the FDA’s vaccine division.

The findings stand in sharp contrast to earlier studies, which found no increased risk—but most of those studies enrolled women who were vaccinated later in pregnancy, beyond the first trimester.

No safety data—yet still recommended

From the outset of the pandemic, pregnant women were urged to get vaccinated despite being excluded from the original clinical trials.

When Pfizer eventually conducted a trial in pregnant women, it included only 173 vaccinated participants, who were vaccinated at 24 to 34 weeks—well past the first trimester.

In the absence of clinical trials, health authorities relied on observational studies—despite well-known limitations like the “healthy vaccinee effect,” where women who opt for vaccination tend to be healthier overall, skewing results.

To overcome these pitfalls, Guetzkow and colleagues adopted a different approach.

Using Israel’s extensive Maccabi Healthcare Services database, they estimated each woman’s risk of foetal loss based on pre-pandemic data (2016–2018), factoring in age, health status, current gestational week, and socio-economic background.

The model was then used to calculate the expected number of foetal losses among vaccinated women by summing the individual risk scores.

Finally, they compared the expected number of losses to the actual number observed.

The danger window: weeks 8 to 13

The strongest signal appeared in women who received their first Covid vaccine dose between 8 and 13 weeks. In this group, there were 3.85 additional losses per 100 pregnancies above the expected rate.

Also, a smaller increase was seen among women who received a booster dose during the same period, with 1.9 additional losses per 100 pregnancies.

“Out of the 3.85 additional foetal losses per 100 pregnancies above expected for dose 1, over 3 occurred from week 14 onward, and slightly under half… occurred from gestational week 25 onward,” the authors reported.

These late-term losses—comprising stillbirths and medically indicated terminations—are unlikely to be explained by behavioural or reporting differences, according to the researchers.

In contrast, women vaccinated during gestational weeks 14 to 27 experienced fewer foetal losses than expected—a pattern the authors attributed to healthy vaccinee bias rather than any protective effect of the vaccine.

The findings were supported by a comparison with pregnancies in which women received the influenza vaccine during the same gestational windows.

In every case, the influenza-vaccinated groups showed lower-than-expected number of foetal losses, reinforcing the notion that women who vaccinate during pregnancy are generally healthier.

Signs the vaccine may interfere biologically

The authors hypothesised several plausible biological explanations for the “higher-than-expected observed number” of foetal losses, including:

• mRNA material crossing the placenta, as shown in recent studies detecting vaccine material in placental and cord blood;

• in vitro evidence that the Pfizer vaccine can suppress genes involved in foetal blood formation;

• and the vaccine’s known risk of triggering blood clots, which are a cause of miscarriage.

A potential dose-response effect was also observed: women who received both Dose 1 and Dose 2 during weeks 8–13 had more losses than those who received only a booster in that window.

A signal hiding in the noise

So why wasn’t this signal detected earlier?

One reason is that only a small fraction—just 9%—of pregnant women in the dataset received their first vaccine dose during this critical window.

The total number of excess foetal losses in this group was just 71 across the cohort—less than 0.4% overall—easily lost in the background noise of seasonal variation and year-to-year trends.

Yet that’s exactly the problem, the authors argue.

“This highlights the importance of developing robust pharmacovigilance methods… to detect weak safety signals in sub-groups of the population,” they wrote.

A policy failure in plain sight

Health officials told pregnant women the vaccines were safe—when no one had studied that claim in the first trimester. This new analysis suggests that serious harms may have been missed.

Commenting on the findings, Levi didn’t hold back.

“The fact that pregnant women were recommended and even pushed to vaccinate during pregnancy without appropriate clinical trials was gross negligence,” he said.

“Public health agencies then tried to retrospectively justify this negligence with observational studies that are known to have fundamental biases. This is bad public health policy. We must do better than that.”

It remains to be seen whether the findings will spark genuine reform. But with Høeg now advising the FDA, and Levi advising the CDC, two of the study’s authors are now working within the very agencies that failed to ask the hard questions.

Could that finally be about to change?

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