Miscarriage is defined as the spontaneous loss of a pregnancy before the 20th week of gestation. This experience is common, occurring in approximately 10 to 20 percent of known pregnancies, with the majority happening in the first trimester. The global presence of the SARS-CoV-2 virus, which causes COVID-19, has generated concern among pregnant individuals about potential added risks. Reviewing scientific data is necessary to understand how the virus and vaccines interact with early pregnancy development. This article examines the current evidence concerning COVID-19 infection, the biological context of the virus in the placenta, and vaccination safety during gestation.
COVID-19 Infection and Miscarriage Risk
The question of whether contracting COVID-19 increases the risk of miscarriage has been a focus of maternal-fetal medicine research since the start of the pandemic. Multiple large-scale studies and systematic reviews have analyzed the rate of early pregnancy loss in individuals who tested positive for SARS-CoV-2. A comprehensive systematic review and meta-analysis, including data from over 168,000 pregnant women, found no statistical indication that SARS-CoV-2 infection in the first or second trimester significantly increases the overall baseline risk of miscarriage.
The background rate of miscarriage in the first trimester of a clinically recognized pregnancy is high, typically falling between 10% and 20%. When researchers compared the rate of miscarriage in infected populations to this established baseline, the figures remained consistent. Some cohort studies suggest a potential increase in risk, particularly in cases where the infection leads to moderate or severe maternal illness. Symptomatic infections that cause systemic distress appear to be the primary concern rather than the presence of the virus itself.
One study involving nearly 27,000 pregnancies suggested that moderate-to-severe COVID-19 infection before or during pregnancy was associated with an increased risk of miscarriage. While overall population data is reassuring, individual outcomes are influenced by the severity of the mother’s illness. The consensus is that while severe COVID-19 illness can lead to adverse pregnancy outcomes later in gestation, the risk of miscarriage is not broadly increased by a mild or asymptomatic infection.
Understanding Biological Interactions in Early Pregnancy
Investigation into the biological interactions between SARS-CoV-2 and the earliest stages of pregnancy helps explain why the risk of miscarriage is not uniformly elevated. The virus gains entry into human cells by binding to the angiotensin-converting enzyme 2 (ACE2) receptor, which is expressed in various tissues throughout the body. This receptor is present in the placenta, particularly in the primitive trophoblast cells that form the initial connection between the developing embryo and the uterine wall.
The presence of ACE2 in these early placental structures suggests a pathway for viral interaction at the fetal-maternal interface. Despite this biological susceptibility, direct viral invasion of the fetus is rare, and the placenta appears to serve as a protective barrier in most cases. The threat to the early pregnancy stems primarily from the maternal body’s reaction to the infection rather than the virus itself.
Severe respiratory illness caused by COVID-19 can trigger a systemic inflammatory response, often referred to as a cytokine storm. This uncontrolled inflammation, accompanied by high fever or hypoxia (low oxygen levels) due to severe lung involvement, can disrupt the hormonal and immunological balance required for a successful early pregnancy. High fever, regardless of its cause, is a known risk factor for adverse outcomes in the first trimester. This remains the most plausible mechanism for any observed increase in miscarriage risk following severe COVID-19.
COVID-19 Vaccination and Miscarriage Safety Data
Concerns that COVID-19 vaccines might pose a risk to the developing pregnancy, particularly in the first trimester, have been extensively addressed by global public health organizations and large-scale safety studies. Data from major public health surveillance systems, such as the U.S. Centers for Disease Control and Prevention’s Vaccine Safety Datalink, have been analyzed to compare miscarriage rates in vaccinated versus unvaccinated groups. These analyses consistently demonstrate that the rate of miscarriage following COVID-19 vaccination is consistent with the expected background rate observed in the general population.
Multiple international studies, including one published in The New England Journal of Medicine, have specifically investigated first-trimester vaccination and found no correlation with an increased risk of pregnancy loss. The pooled miscarriage rate among vaccinated women was approximately 9%. This aligns with the historical rates of miscarriage in uninfected populations. This finding applies across different vaccine types, including the mRNA vaccines, and regardless of the timing of the dose.
The mechanism of the mRNA vaccines supports their safety profile, as they introduce genetic instructions to create a spike protein fragment, not the live virus itself. The vaccine components do not cross the placenta to reach the fetus and cannot alter human DNA. The scientific consensus is that the benefits of vaccination—primarily preventing severe maternal illness—far outweigh any theoretical risk, as the vaccine does not increase the risk of miscarriage.
Protective Measures for Pregnant Individuals
Since severe maternal illness is the primary driver of adverse pregnancy outcomes, the most important protective measure is vaccination against SARS-CoV-2. Vaccination is strongly recommended for pregnant individuals to prevent severe COVID-19, which carries an increased risk of complications like intensive care admission. This preventative step mitigates the risk associated with the virus and protects both the birthing person and the fetus.
Standard public health practices remain relevant for pregnant individuals to minimize exposure to the virus. These measures include frequent hand washing, wearing a high-quality mask in crowded indoor settings, and maintaining physical distance from others. Pregnant individuals should discuss their specific risk factors and circumstances with their healthcare provider. This consultation ensures that preventative measures align with the individual’s medical history and current health status.