Moderna COVID-19 Vaccine and Placental Blood Clots in Pregnancy
There is no evidence that the Moderna COVID-19 vaccine increases the risk of placental blood clots in pregnant women. In fact, COVID-19 infection itself poses a greater risk of thrombotic complications during pregnancy than vaccination.
COVID-19 Infection and Thrombotic Risk in Pregnancy
- Pregnancy is inherently a hypercoagulable state with a 4-6 fold increased risk of venous thromboembolism (VTE) compared to non-pregnant women 1
- COVID-19 infection during pregnancy can exacerbate this hypercoagulable state, potentially leading to:
- Case reports have documented severe placental thromboembolism in COVID-19 infected pregnant women, associated with fetal death 5
COVID-19 mRNA Vaccines and Thrombotic Risk
- Analysis of the US Vaccine Adverse Event Reporting System (VAERS) found only 61 cases of thromboembolic events among 13.6 million women aged ≤50 years who received Pfizer-BioNTech or Moderna COVID-19 vaccines (1 case per 222,951 vaccinated) 6
- No disproportional reporting of thromboembolic events was found for mRNA COVID-19 vaccines compared to baseline rates 6
- The CDC recommends COVID-19 vaccination for all people aged 12 years and older, including pregnant women 4
- Real-world data from 90,000 pregnant women collected through the V-safe COVID-19 vaccine pregnancy registry did not identify any safety signals related to thrombotic events 4
Benefits of COVID-19 Vaccination During Pregnancy
- COVID-19 vaccination during pregnancy has been shown to:
- Reduce risk of SARS-CoV-2 infection by 60% 7
- Reduce risk of COVID-19 hospitalization during pregnancy by 53% 7
- Reduce risk of COVID-19 ICU admission by 82% 7
- Reduce risk of stillbirth by 45% 7
- Reduce risk of preterm birth by 15-33% depending on gestational age 7
- Reduce risk of neonatal ICU admission by 20% 7
Thromboprophylaxis Recommendations for Pregnant Women
- For pregnant women with COVID-19 infection requiring hospitalization, weight-adjusted VTE prophylaxis with low molecular weight heparin (LMWH) is recommended in the absence of active bleeding 1
- Thromboprophylaxis should be considered for pregnant women with COVID-19 managed at home if they have risk factors such as immobility, high fever, dehydration, or additional maternal risk factors for VTE 1
- The duration of thromboprophylaxis should be individualized based on disease severity, D-dimer levels, and trimester of pregnancy 1
Key Considerations for Clinical Practice
- The risk of thrombotic complications is significantly higher with COVID-19 infection than with COVID-19 vaccination 4, 7
- Pregnant women are at increased risk for severe COVID-19 disease compared to non-pregnant women of reproductive age 4
- The International Society on Thrombosis and Haemostasis (ISTH) has established an international registry to gather more data on coagulopathies in COVID-19-affected pregnancies 1
In conclusion, current evidence strongly supports that the Moderna COVID-19 vaccine does not increase the risk of placental blood clots, while COVID-19 infection itself poses significant thrombotic risks during pregnancy.