A recent large-scale study conducted by researchers at Massachusetts General Hospital has found that babies born to mothers who contracted COVID-19 during pregnancy show a slightly increased likelihood of receiving neurodevelopmental diagnoses by the age of three. These conditions mainly include speech and motor delays. The association was most pronounced when infection occurred late in pregnancy, particularly in the third trimester, and was more evident in male children. While the increase in risk for any individual child was small, because millions of women were pregnant during the pandemic, even a modest rise in such risks could have significant public health implications.
The study reviewed medical records of over 18,000 mother-child pairs who gave birth between March 2020 and May 2021, a period before COVID-19 vaccines were widely available. During this time, universal testing for COVID-19 was implemented for all women giving birth, allowing researchers to clearly identify which pregnancies were exposed to the virus. Approximately 5% of these mothers tested positive for COVID-19 during pregnancy. After adjusting for various factors such as maternal age, race, insurance status, and preterm birth, children born to mothers infected with COVID-19 were found to be modestly more likely to be diagnosed with neurodevelopmental disorders by age three compared to children whose mothers were not infected.
Dr. Andrea Edlow, a maternal-fetal medicine specialist and one of the study’s authors, emphasized the strength of the study due to the universal testing early in the pandemic. “This was a very clean group to follow,” she said, underscoring the clarity of exposure data. The study’s findings align with existing knowledge about infections during pregnancy: maternal infections and the resulting inflammation can influence fetal brain development. This is not unique to COVID-19; similar patterns have been observed with other infections.
Dr. Alan Brown, a psychiatry and epidemiology expert at Columbia University who studies maternal infections and their impact on brain development, noted that COVID-19 is a strong candidate for causing neurodevelopmental effects because it often triggers a powerful inflammatory response. Inflammation during pregnancy can affect the developing brain by disrupting processes critical to brain growth, such as synaptic pruning — a natural process where immune cells in the brain remove unnecessary neural connections to shape proper brain circuitry.
Animal studies support these observations. Experiments in pregnant mice that simulate inflammation show offspring with altered brain cell growth and connectivity, leading to changes in learning and behavior. In humans, the fetal brain undergoes rapid growth and neural connection formation especially during the third trimester, which may explain why infections late in pregnancy have a stronger association with developmental delays. Dr. Roy Perlis, vice chair for research in psychiatry at Massachusetts General Hospital and co-author of the study, explained that while organ development generally occurs earlier in pregnancy, brain development continues robustly into the third trimester and beyond, making this period particularly vulnerable.
However, some experts caution against overinterpreting the timing of infection. Dr. Brian Lee, a professor of epidemiology at Drexel University, pointed out that most COVID-19 tests in the study were conducted at delivery, which means the data is weighted toward identifying late-pregnancy infections. This might have given the study more power to detect effects in the third trimester, but it does not conclusively rule out risks from earlier infections.
The study also revealed a stronger impact on male children, a finding consistent with broader research indicating that boys are generally more susceptible than girls to neurodevelopmental issues such as speech delays, motor delays, and autism. Though the exact biological mechanisms are not fully understood, it is suspected that male fetuses may be more sensitive to prenatal stress and inflammation.
Despite these findings, the authors and other experts emphasize that the study shows an association rather than definitive causation. Many confounding factors could contribute to the observed relationship. For example, mothers who become ill with COVID-19 may also have other health challenges such as obesity, diabetes, or mental health conditions, all of which could independently increase the risk of developmental delays in their children. Dr. Lee highlighted that women with mental disorders are more likely both to contract COVID-19 and to have children with neurodevelopmental problems, suggesting that genetics or environmental factors might also play a role.
Further complicating the picture, Dr. Lee’s own research has found links between infections occurring outside pregnancy and autism risk, implying that shared familial or environmental factors, rather than the infection itself, might explain some associations. Because of these complexities, experts agree that much larger and longer-term