This article presents a detailed analysis of a study published in the journal *Environmental Health Perspectives* 2005;113:602-606. The study aims to estimate the relationship between air pollution levels commonly observed in four counties in Pennsylvania and the number of preterm births. The method relies on time-series analysis to quantify the average and acute effects of pollution on the risk of preterm births. The study period spans from 1997 to 2001, and the pollutants considered are particulate matter with an aerodynamic diameter of less than 10 μm (PM10) and sulfur dioxide (SO2). The health effects of pollutant levels observed during the six weeks preceding birth, as well as the health effects of levels observed a few days before birth, were analyzed. This study appears to be novel due to the method employed and the large amount of data used. To make it more original, the authors could have tested other scenarios of increased air pollution levels and other time windows instead of adhering to those in the existing literature. Conducting further studies based on time-series analyses should help validate the results obtained and deepen our understanding of the subject.