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Beate Ritz^1,2 and Fei Yu³

¹Department of Epidemiology; ²Center for Occupational and Environmental Health; and ³Department of Biostatistics, School of Public Health, UCLA, Los Angeles, CA 90095 USA

Abstract

We evaluated the effect of carbon monoxide (CO) exposures during the last trimester of pregnancy on the frequency of low birth weight among neonates born 1989-1993 to women living in the Los Angeles, California, area. Using birth certificate data for that period, we assembled a retrospective cohort of infants whose mothers resided within 2 miles of 1 of 18 CO monitoring stations. Based on the gestational age and birth date of each child, we estimated last-trimester exposure by averaging the corresponding 3 months of daily CO concentrations registered at the monitoring station closest to the mother's residence (determined from the birth certificate) . Where data were available (at 6 stations) , we also averaged measurements taken daily for nitrogen dioxide and ozone and those taken at 6-day intervals for particulate matter 10 µm (PM₁₀) to approximate last-trimester exposures to other pollutants. Overall, the study cohort consisted of 125,573 singleton children, excluding infants born before 37 or after 44 weeks of gestation, those weighing below 1,000 or above 5,500 g at birth, those for whom fewer than 10 days of CO measurements were available during the last trimester, and those whose mothers suffered from hypertension, diabetes, or uterine bleeding during pregnancy. Within the cohort, 2,813 (2.2%) were low in birth weight (between 1,000 and 2,499 g) . Exposure to higher levels of ambient CO (>5.5 ppm 3-month average) during the last trimester was associated with a significantly increased risk for low birth weight [odds ratio (OR) = 1.22 ; 95% confidence interval (CI) , 1.03-1.44] after adjustment for potential confounders, including commuting habits in the monitoring area, sex of the child, level of prenatal care, and age, ethnicity, and education of the mother. Key words: air pollution, carbon monoxide, environmental hazard surveillance, epidemiology, health effects, low birth weight. Environ Health Perspect 107:17-25 (1999) . [Online 7 December 1998]

http://ehpnet1.niehs.nih.gov/docs/1999/107p17-25ritz/ abstract.html

Address correspondence to B. Ritz, Department of Epidemiology, School of Public Health, UCLA, PO Box 951772, Los Angeles, CA 90095-1772 USA.

We thank Arthur Winer for numerous suggestions and support throughout the project. We received invaluable assistance from members of the SCAQMD, specifically J. Cassmassi. We thank Darin Hanson for help with the air monitoring data and Guadalupe Chapa and Scott Fruin for assistance with mapping of air monitoring stations. We extend special thanks to Bambi Batts Young for many helpful comments and editing.

This study was supported by a pilot grant (# PO H07172) as part of the UCLA-USC NIEHS center grant (# 5P30ES70048) .

Received 27 May 1998 ; accepted 10 August 1998.