Objective: To evaluate the effect of 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.
Approach: Birth certificate data for the period 1989-1993 were used to assemble 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, last-trimester exposure was estimated by averaging the corresponding 3 months of daily CO concentrations registered at the monitoring station closest to the mother's residence. Measurements of daily NO2 and O3, where available, and that for particulate matter [less than/equal to]10 microns (PM10) were used.
Results: The study cohort consisted of 125,573 singleton children. Excluded were 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.
Conclusion: Levels of environmental CO previously thought to be extremely low were shown to lower birth weight in women exposed to CO during the last trimester of pregnancy.
Location of authors: Department of Epidemiology; Center for Occupational and Environmental Health, School of Public Health, UCLA, Los Angeles, CA 90095 USA
From: Ritz, B. & Yu, F. (1999) The effect of ambient carbon monoxide on low birth weight among children born in southern California between 1989 and 1993. Environmental Health Perspectives, 107, 17-25.
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