“COVID vaccination during or before pregnancy did not increase miscarriage risk above expected background rates.”

• Magnus et al., NEJM (2021) — Norwegian registry study of ~18,000 pregnant women found no increased risk of first-trimester miscarriage after COVID-19 vaccination (adjusted OR ~0.9–1.0 for both mRNA vaccines).
• Kharbanda et al., JAMA (2021) — Vaccine Safety Datalink case-control surveillance across 8 US health systems found COVID-19 vaccination in the prior 28 days was not associated with spontaneous abortion (aOR ~0.8).
• Zauche et al., NEJM (2021) — CDC analysis of v-safe pregnancy registry participants vaccinated preconception or before 20 weeks found cumulative spontaneous abortion risk (~13%) within the expected background range of 11–22%.
• Shimabukuro et al., NEJM (2021) — preliminary v-safe/VAERS safety data in >35,000 pregnant people showed adverse pregnancy outcomes, including spontaneous abortion, at rates similar to pre-pandemic historical baselines.
• Prasad et al., Nature Communications (2022) — systematic review/meta-analysis of COVID-19 vaccination in pregnancy found no increase in miscarriage or other adverse perinatal outcomes, plus benefits against severe maternal COVID-19.
• Background miscarriage rates are high (roughly 11–22% of recognized pregnancies), and large denominators in the above studies were adequate to detect a meaningful excess; multiple independent datasets in different countries converged on null findings.
• Major agencies and professional bodies (CDC, ACOG, SMFM, WHO, UK MHRA/JCVI) reviewed this evidence and concluded vaccination does not increase miscarriage risk.

• The initial NEJM v-safe paper (Shimabukuro 2021) had a denominator problem — many enrollees vaccinated in the third trimester had not yet completed pregnancy — which was later corrected; critics correctly noted the first published version could not properly estimate first-trimester miscarriage risk (the corrected and follow-up analyses still showed no excess).
• Pivotal randomized trials excluded pregnant participants, so all reassurance rests on observational data, which can be affected by confounding, exposure misclassification, and 'healthy vaccinee' selection bias.
• Very early pregnancy losses (pre-clinical/chemical pregnancies) are poorly captured in registry and EHR data, so an effect on the earliest losses is harder to exclude, though studies of conception cohorts also found no effect.
• Some subgroup or small-sample estimates have wide confidence intervals, meaning small relative risk changes (e.g., <10–20%) in specific windows cannot be excluded with absolute certainty.
• The claim's phrase 'before pregnancy' is supported by fewer dedicated studies (preconception cohorts such as PRESTO and the v-safe preconception subgroup) than the in-pregnancy evidence base.

93/100 — the lab’s own confidence in the score above, not a second reading of the claim.

New England Journal of Medicine (Magnus et al., Norwegian Institute of Public Health)journal · 96 · JAMA (Kharbanda et al., Vaccine Safety Datalink)journal · 95 · New England Journal of Medicine (Zauche et al., CDC v-safe)journal · 94 · New England Journal of Medicine (Shimabukuro et al.; note published correction)journal · 90 · Nature Communications (Prasad et al., systematic review/meta-analysis)journal · 92 · FactCheck.org (SciCheck)factcheck · 88 · CDC MMWRgov · 90

• Large U.S. Vaccine Safety Datalink case-control study in JAMA found no association between COVID-19 vaccination in the prior 28 days and spontaneous abortion: adjusted odds ratio 1.02, essentially null, across 105,446 pregnancies.
• CDC v-safe pregnancy registry analysis in NEJM estimated miscarriage risk after mRNA vaccination before 20 weeks at about 12.8% age-standardized, within expected background ranges for recognized pregnancies.
• Norwegian registry case-control study in NEJM found no increased odds of first-trimester miscarriage after COVID-19 vaccination, including vaccination in the prior 3 or 5 weeks.
• CDC and NHS guidance summarize surveillance and epidemiologic evidence as showing no safety signal that COVID-19 vaccination before or during pregnancy increases miscarriage risk.
• The expected background miscarriage rate is substantial, so miscarriages occurring after vaccination are expected by chance; controlled studies comparing vaccinated and unvaccinated pregnancies do not show excess risk.

• No strong, well-controlled evidence was found that COVID-19 vaccination before or during pregnancy increases miscarriage risk above background rates.
• Caveat: early safety reports had limited completed first-trimester pregnancy outcomes, and evidence is strongest for mRNA vaccines and studied populations; very small risks in narrow subgroups or for less-used vaccine platforms cannot be ruled out with absolute certainty.
• Passive surveillance systems such as VAERS contain reports of miscarriage after vaccination, but VAERS reports alone cannot establish causation or an elevated rate, and controlled studies have not confirmed an excess risk.

92/100 — the lab’s own confidence in the score above, not a second reading of the claim.

JAMAjournal · 95 · New England Journal of Medicinejournal · 95 · New England Journal of Medicinejournal · 95 · New England Journal of Medicinejournal · 92 · Centers for Disease Control and Preventiongov · 92 · U.S. Department of Health and Human Services / VAERSgov · 85

• Extensive real-world data and peer-reviewed studies have consistently shown that COVID-19 vaccination does not increase the risk of spontaneous abortion (miscarriage).
• A comprehensive study published in the New England Journal of Medicine (Zauche et al., 2021) analyzed data from the CDC's v-safe pregnancy registry and found the cumulative risk of spontaneous abortion after mRNA COVID-19 vaccination was 14.1%, which is well within the expected background rate of 11% to 22%.
• A large case-control study published in JAMA (Kharbanda et al., 2021) analyzing over 105,000 pregnancies found that receiving an mRNA COVID-19 vaccine during pregnancy was not associated with an increased risk of miscarriage within the subsequent 28 days.
• Major medical organizations, including the American College of Obstetricians and Gynecologists (ACOG) and the Centers for Disease Control and Prevention (CDC), strongly recommend COVID-19 vaccination before and during pregnancy based on definitive safety data.

• Because pregnant individuals were routinely excluded from the initial Phase 3 clinical trials of the COVID-19 vaccines, there was a temporary gap in randomized controlled trial data regarding pregnancy outcomes at the very beginning of the vaccine rollout.
• There are raw, unverified anecdotal reports of miscarriage following vaccination submitted to the Vaccine Adverse Event Reporting System (VAERS). However, epidemiologists note that because miscarriages are naturally common, background rates guarantee thousands will coincidentally occur shortly after vaccination without the vaccine being the cause.

99/100 — the lab’s own confidence in the score above, not a second reading of the claim.

New England Journal of Medicinejournal · 98 · JAMAjournal · 98

• A CDC v-safe registry analysis published in the New England Journal of Medicine estimated spontaneous-abortion risk after mRNA vaccination before conception or during pregnancy at 14.1% unadjusted and 12.8% after maternal-age standardization, concluding that the risk was consistent with expected background risk. Reliability: 98/100.
• A large prospective cohort study published in Human Reproduction found no increased miscarriage rate when either partner received a COVID-19 vaccine before conception; miscarriage risk was 23.9% among vaccinated female participants versus 26.6% among unvaccinated participants. Reliability: 96/100.
• A 2023 systematic review and meta-analysis in Human Reproduction found a pooled miscarriage rate of 9% among 123,185 vaccinated women and concluded that the evidence did not indicate increased miscarriage risk compared with expected rates. Reliability: 94/100.
• The CDC states that studies involving more than one million pregnant women found no increased health risks from COVID-19 vaccination before or during pregnancy. Reliability: 97/100.
• FactCheck.org, PolitiFact, and AFP Fact Check reviewed recurring claims that vaccination increases miscarriage and found them unsupported by large-scale epidemiologic evidence. Reliability: 88/100.

• Early surveillance evidence had important limitations: the initial NEJM v-safe report included only 827 completed pregnancies, lacked a concurrent unvaccinated comparison group, and relied partly on passive or self-reported reporting. These limitations reduced certainty at the time, although later comparative studies addressed them. Reliability: 90/100.
• The initial v-safe analysis reported 104 spontaneous abortions among 827 completed pregnancies, or 12.6%. That raw figure could be misinterpreted because pregnancies ending early were less likely to have been completed and reported; the authors therefore used gestational-age and maternal-age-adjusted analyses. This is a limitation of the early evidence, not evidence that vaccination caused excess miscarriages. Reliability: 98/100.
• Some observational studies report miscarriage proportions within vaccinated cohorts, such as 10.9% in a 2025 cohort study, but they do not establish increased risk without an appropriate comparison group. The available study itself reported that its findings were consistent with no excess risk. Reliability: 88/100.
• The claim is broad because vaccine products, schedules, variants, populations, and timing differ, and evidence is strongest for mRNA vaccines and for vaccination before or during early pregnancy. Therefore, the statement should not be read as proving zero risk or as covering every possible vaccine formulation equally well. Reliability: 92/100.

96/100 — the lab’s own confidence in the score above, not a second reading of the claim.

New England Journal of Medicinejournal · 98 · New England Journal of Medicinejournal · 98 · Human Reproduction / Oxford Academicjournal · 96 · Human Reproduction / Oxford Academicjournal · 94 · Centers for Disease Control and Preventiongov · 97 · FactCheck.orgfactcheck · 88 · FactCheck.orgfactcheck · 88 · PolitiFactfactcheck · 87 · AFP Fact Checkfactcheck · 87 · Scientific Reportsjournal · 89

• Large U.S. and international observational studies and pregnancy registries (including CDC v-safe/VSD analyses) reported first-trimester miscarriage rates of roughly 12–15% after COVID-19 vaccination, matching the well-established background rate of 10–20% for clinically recognized pregnancies.
• A Norwegian national registry analysis found no increased risk of first-trimester miscarriage associated with COVID-19 vaccination during pregnancy.
• CDC, ACOG, SMFM and WHO have consistently stated that COVID-19 vaccines do not raise miscarriage risk and recommend vaccination before or during pregnancy; multiple systematic reviews and meta-analyses of observational data reach the same conclusion.
• Studies of vaccination before conception (including IVF cohorts) likewise show no elevation in subsequent miscarriage rates above background.

• VAERS and similar passive-report systems contain miscarriage reports after vaccination, which some commentators treat as evidence of risk; these systems lack denominators, suffer from stimulated reporting, and cannot measure incidence or causation.
• A minority of commentaries and lower-quality analyses (often using incomplete follow-up or incorrect denominators that mix ongoing pregnancies with completed ones) have claimed elevated rates; these have been contradicted by subsequent complete-data studies.
• Very early (pre-clinical) losses are difficult to capture in any observational design, leaving a residual uncertainty that critics sometimes emphasize even though available data show no signal above background.

86/100 — the lab’s own confidence in the score above, not a second reading of the claim.

New England Journal of Medicinejournal · 96 · New England Journal of Medicinejournal · 96 · American College of Obstetricians and Gynecologistsother · 90