Outdoor air pollution continues to be a challenging health issue, even as countries experience economic growth. By exploiting a unique transboundary setting in East Asia, we study the impact of an increase in particulate matter (PM) concentrations on fetal deaths. Due to the westerlies in the mid-latitudes, residents in South Korea at times experience intermittent exposure to high levels of air pollution. Using such atmospheric setting, we estimate a reduced-form impact of high PM events on fetal deaths, which captures in utero exposure to pollution. Controlling for local weather and pollution trends, regression results indicate that high PM events in Beijing lead to a significant increase in daily fetal mortality rates in Korea, by approximately 7.4 per cent. This research finding provides lower-bound estimates of not only negative spillovers manifested in fetal health but also the impact of pollution on the health of the Chinese population and calls for a need to tackle transboundary air pollution via international cooperation.