When Does Air Quality Affect Preterm Delivery?

October 29, 2014

Exposure to air pollution during a specific period in a pregnancy is associated with a significant risk of preterm delivery before 37 weeks.

Preterm delivery is a complication that affects as many as 12% of pregnancies. Air pollution is one of the many factors that could be important in the risk for premature labor. In the first weeks of pregnancy, women might not even know that they are indeed pregnant and are, therefore, not able to identify and avoid environmental conditions that could negatively affect the fetus. Air pollution might be difficult to avoid, but there are measures that pregnant women can take to protect their pregnancy, especially if they know the most critical time that pollution affects a growing fetus. A study published in the September 2014 issue of Fertility and Sterility and presented at ASRM 2014 looks at the specific risks of air pollution in very early pregnancy.

A large retrospective cohort study was done to determine the affect pollution might have during 4 separate windows in pregnancy: between weeks 1 and 7, 8 and 14, 15 and 21, and 22 and 28. Information from 223,194 singleton deliveries between 2002 and 2008 from the U.S. Consortium on Safe Labor were analyzed to find those births that occurred before 37 weeks' gestation. Researchers then correlated the 11.7% of deliveries that were defined as preterm with Community Multiscale Air Quality models.

The air quality was found to be similar during the course of the study period and across the defined gestational windows. However, women who were exposed to a peak of a 10 unit change in air pollution during the first gestational window (between 1 and 7 weeks) were more likely to deliver their babies early than those who were not. The air pollutants that researchers concluded had the most effect on this higher risk included small particulate matter (2.5 microns or smaller), big particulate matter (10 microns or smaller), and nitric oxides. No difference was found in the preterm delivery rate between women who had received assisted reproductive technology and those who did not. Exposure to peak air pollution during the other gestational windows was associated with a lower risk of preterm delivery than during the first window.