Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts
Ambient air pollution exposures have been linked to hypertension and other cardiovascular events. Air pollution has also been associated with preterm delivery, of which preeclampsia is considered to be an important risk factor. Maternal hypertension during pregnancy is one of the symptoms of preeclampsia. We evaluate the relationship between air pollution and preeclampsia in pregnant women in California to assess the possible contribution of air pollution to preeclampsia.
Data and Methods:
Birth certificate information for California between 1996 and 2004 was linked to air pollution monitoring data from the California Air Resources Board. Singleton live birth, gestational age between 32 and 44 weeks and a plausible birth weight were eligible for the study. We assigned air pollution estimates for each singleton live birth by the mother’s residence at the time of birth. We required a valid geo-code for mother’s residence (1990 census tract, 2000 census tract, or 2000 ZIP Code Tabulation Area), and monitors with valid pollutant exposure estimate for any of the six criteria air pollutants for particulate matter (PM2.5, PM10 and course PM), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. We coded each maternal address to the corresponding census tract and zipcode. We projected the selected monitors onto a California map in the Teale-Albers projection. We then calculated a network of Theissen polygons to define the region closest to each monitor. For geo-codes entirely contained in one of the Thiessen polygons, we assigned the concentration estimate of that polygon’s monitor. For geo-codes spanning more than one of these Thiessen polygons, we created an area-weighted average based on the area of the geo-code closest to each monitor. We then generated an average exposure estimate for the entire pregnancy. Conditions of preeclampsia and eclampsia coded on the birth certificate were evaluated for those women who had at adequate prenatal care and who did not have pre-existing chronic conditions such as hypertension, diabetes, heart disease or kidney problems prior to pregnancy. Logistic regression was used to evaluate the relationship between air pollution and outcomes, accounting for maternal characteristics on the birth certificate (race, age, parity, marital status, maternal education), neighborhood characteristics (poverty, unemployment, home ownership rates), and year and season of exposure.
Our analysis included 2,307,366 births. After adjustment for maternal characteristics and neighborhood demographic we found adjusted odds ratios of 1.08 [95% confidence interval (CI), 1.02–1.14] for high CO exposures (>75th percentile) among mothers during their entire pregnancy who were residing within a 10 kilometer distance of a monitor. We also observed an elevated odds ratio of 1.14 [95% confidence interval (CI), 1.05–1.23] for high SO2 exposures (>75th percentile). We did not find consistent positive relationships between other air pollutant exposures and risk of pre-eclampsia and eclampsia.
This study suggests that maternal CO and SO2 exposure during pregnancy may be a risk factor for pre-eclampsia and eclampsia. Given the paucity of research on this subject, the association between air pollution exposures and risk pre-eclampsia and eclampsia should be further studied.