The possibility that COVID-19 vaccines increase the risk of miscarriage has been a significant public concern since their availability. Miscarriage, medically termed spontaneous abortion, is the most common complication of early pregnancy. It is estimated that between 10% and 20% of all known pregnancies naturally end in miscarriage, with the majority occurring in the first trimester. Major health organizations worldwide have consistently reviewed the evidence and concluded that there is no link between receiving a COVID-19 vaccine and an increased risk of pregnancy loss.
Large-Scale Data on Vaccine Safety and Miscarriage Rates
The safety profile of the COVID-19 vaccines during pregnancy has been closely monitored by multiple large-scale surveillance systems and epidemiological studies. These investigations compared the rate of pregnancy loss in vaccinated individuals to historical background rates and the rates seen in unvaccinated control groups. Data from the V-safe Pregnancy Registry, a voluntary monitoring system in the United States, provided some of the earliest and largest datasets.
Analysis of this extensive data showed that the rate of miscarriage among vaccinated people was consistent with the expected background rate in the general population. For example, a study published in the New England Journal of Medicine using Norwegian registry data examined nearly 18,500 pregnancies. The results demonstrated no elevated risk for early pregnancy loss after COVID-19 vaccination, even when administered within the first trimester.
This period is relevant because the vast majority of miscarriages occur before the 13th week of gestation. Detailed analyses confirmed that the observed spontaneous abortion rate in vaccinated people was approximately 12.6% to 13%. This rate falls squarely within the established range of 11% to 22% for known pregnancies. These findings provide strong statistical reassurance, indicating that the vaccines do not introduce an additional risk factor for early pregnancy loss.
Biological Explanation of Vaccine Action and Fetal Safety
The scientific understanding of how the vaccines work provides a clear biological explanation for their safety during pregnancy. The most common COVID-19 vaccines are messenger RNA (mRNA) vaccines, which do not contain live virus particles that could cause infection in the mother or the developing fetus. Instead, the mRNA acts as temporary instructions, directing the body’s cells to produce a harmless piece of the SARS-CoV-2 spike protein.
Once these instructions are delivered, the immune system recognizes the protein and creates protective antibodies. The mRNA molecules are fragile and are quickly broken down by the body’s normal cellular processes, typically within a few days. The vaccine components, including the mRNA and the resulting spike protein, largely remain localized to the injection site in the muscle and nearby lymph nodes.
The placenta serves as an effective biological barrier. Studies using human placental tissue have detected minimal to no intact vaccine mRNA crossing this barrier to reach the fetus. Instead of vaccine components, the beneficial maternal antibodies generated by the immune response are actively transferred across the placenta to the fetus. This process provides the newborn with passive immunity, offering protection from the virus after birth.
Documented Risks of COVID-19 Infection During Pregnancy
While the vaccines have been proven safe, the risks associated with contracting SARS-CoV-2 during pregnancy are substantial and well-documented. Pregnant individuals are at an elevated risk of experiencing severe illness from COVID-19 compared to their non-pregnant peers. Infection can lead to a higher likelihood of requiring intensive care unit admission, mechanical ventilation, and other forms of severe maternal morbidity.
The infection also poses direct threats to the pregnancy itself, significantly increasing the risk of adverse outcomes. Studies have shown that maternal COVID-19 infection is associated with an increased chance of pre-term birth, which occurs before 37 weeks of gestation. The virus can also raise the risk of preeclampsia, a serious condition characterized by high blood pressure and signs of damage to other organ systems.
The risk of stillbirth, defined as fetal death after 20 weeks of pregnancy, is higher in individuals infected with SARS-CoV-2. The inflammatory response and vascular changes caused by the viral infection contribute to these negative outcomes. This established pathology highlights that vaccination mitigates the proven dangers posed by the natural infection.
Current Public Health Recommendations
Based on extensive safety data and documented risks of infection, leading medical and public health organizations strongly recommend COVID-19 vaccination for all eligible individuals who are pregnant, breastfeeding, or planning pregnancy. The American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO) have been unwavering in this guidance. This recommendation emphasizes the protective benefits for both the pregnant person and the developing baby.
The vaccine can be administered at any point during pregnancy, and there is no preferred trimester for vaccination. Receiving a vaccine dose at the earliest opportunity is encouraged to maximize protection against the virus throughout the pregnancy. Updated booster shots are also recommended to ensure the highest level of antibody protection, especially as immunity wanes over time and new viral variants emerge. Clinicians are advised to counsel their patients on the safety and efficacy data, reinforcing that vaccination is a safe and important step toward a healthy pregnancy.