Miscarriage is defined as the spontaneous loss of a pregnancy before the 20th week of gestation. This early pregnancy loss is common, and the COVID-19 pandemic introduced new concerns for expectant parents regarding pregnancy safety. The rapid spread of SARS-CoV-2, coupled with limited initial data, created significant anxiety. Understanding the true risks associated with this viral infection is necessary for accurate risk assessment and informed decision-making.
The Current Scientific Consensus on Early Pregnancy Loss
Large-scale epidemiological studies generally agree that a mild or asymptomatic SARS-CoV-2 infection does not significantly increase the risk of miscarriage beyond the established background rate. Systematic reviews have found no statistically significant association between COVID-19 infection during the first or second trimester and a higher rate of spontaneous abortion. The rates observed in women with mild COVID-19 infection typically fall within the expected range for the general population.
However, the data are not entirely uniform, as some large cohort studies have suggested a potential increase in risk. For example, one analysis indicated that women infected with COVID-19 faced a two to three times greater risk of miscarriage compared to uninfected controls. Another study reported a higher rate of spontaneous miscarriage in COVID-19 positive patients, finding no direct correlation between miscarriage risk and the severity of the mother’s symptoms.
This complexity suggests that while severe illness is a clear risk factor for later complications, the direct link between a typical, non-hospitalized COVID-19 case and miscarriage is not strongly established. The miscarriage rate among infected individuals remains close to the expected rate for the general pregnant population. Differences in study findings may reflect variations in cohort populations, circulating viral variants, and how infection was diagnosed. The majority of robust analyses indicate that mild or asymptomatic infection does not pose an additional threat for early pregnancy loss.
Potential Biological Causes of Fetal Harm
While the statistical link between COVID-19 and miscarriage is debated, potential harm centers on the mother’s systemic reaction rather than direct fetal infection. SARS-CoV-2 rarely crosses the placenta in early pregnancy, but the mother’s body mounts a powerful inflammatory response. This systemic inflammation, sometimes called a “cytokine storm” in severe cases, involves signaling molecules that can disrupt the delicate processes of early gestation.
The inflammatory environment created by the infection can interfere with the complex immunology of the maternal-fetal interface, which is required for successful implantation and development. Elevated levels of inflammatory cytokines in the maternal bloodstream can cross the placenta and induce an inflammatory response in the developing fetus. This indirect effect can potentially compromise the function of the early placenta.
Maternal fever, or hyperthermia, is another potential mechanism of fetal harm and is a common symptom of severe infection. Elevated core body temperature, particularly early in the first trimester, is a recognized teratogen that can disrupt embryonic development and increase the risk of adverse outcomes, including miscarriage. Furthermore, placental pathology has been observed in some cases of maternal COVID-19, which can impair the placenta’s ability to provide oxygen and nutrients to the fetus.
The Protective Role of Vaccination During Pregnancy
Given the documented risks associated with severe maternal COVID-19, vaccination during pregnancy is an important consideration for prevention. Extensive data from large-scale studies have consistently shown that COVID-19 vaccination is not associated with an increased risk of miscarriage, congenital anomalies, or other adverse pregnancy outcomes. Major health organizations worldwide recommend vaccination for pregnant individuals at any stage of gestation.
Vaccination works by reducing the likelihood of a severe maternal infection, which is the primary driver of complications during pregnancy. By preventing the severe systemic inflammation and high fevers that accompany serious illness, the vaccine indirectly protects the pregnancy from biological harm. Studies show that vaccinated pregnant individuals face a much lower risk of being admitted to an intensive care unit or requiring mechanical ventilation due to COVID-19.
The protection extends to the fetus and newborn through the transfer of maternal antibodies across the placenta. This passive immunity provides the infant with a defense against SARS-CoV-2 in the first months of life. The evidence demonstrates that the vaccine is safe and provides a significant protective benefit for both the pregnant person and the baby. The benefits of vaccination far outweigh any theoretical risks.
Clarifying Miscarriage Versus Later Adverse Outcomes
It is important to distinguish between the timing of pregnancy loss when evaluating the impact of COVID-19 infection. Miscarriage refers specifically to a pregnancy loss occurring before the 20th week of gestation. Fetal loss after this point is medically defined as a stillbirth.
While the epidemiological link between SARS-CoV-2 infection and miscarriage is generally weak, the association between severe COVID-19 and later adverse outcomes is much clearer. Severe infection, particularly in the second or third trimester, has been associated with an increased risk of complications such as preterm birth and preeclampsia. Unvaccinated pregnant individuals with COVID-19 have a substantially higher risk of stillbirth compared to uninfected mothers, sometimes up to four times greater during periods when virulent variants circulated.
This distinction highlights that the greatest risk to a pregnancy from COVID-19 lies in the potential for severe maternal disease later in gestation. The resulting systemic stress, inflammation, and placental damage contribute to poor outcomes like stillbirth and preterm delivery. Understanding these differences is essential for accurate risk assessment and appropriate medical management throughout pregnancy.