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Air Pollution and Adverse Birth Outcomes in the South Coast Air Basin, 1989-2000

Air Pollution and Adverse Birth Outcomes in the South Coast Air Basin, 1989-2000. Michelle Wilhelm, Ph.D. Beate Ritz, M.D., Ph.D. Department of Epidemiology UCLA School of Public Health. Why Study Air Pollution and Pregnancy ?.

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Air Pollution and Adverse Birth Outcomes in the South Coast Air Basin, 1989-2000

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  1. Air Pollution and Adverse Birth Outcomes in the South Coast Air Basin, 1989-2000 Michelle Wilhelm, Ph.D. Beate Ritz, M.D., Ph.D. Department of Epidemiology UCLA School of Public Health

  2. Why Study Air Pollution and Pregnancy? • Developing organism is uniquely sensitive to environmental toxins within a short time window • Adverse outcomes are common; in US: • ~10% are preterm • ~ 5% are low weight • Immediate and long term health effects • Infant morbidity and mortality • Adverse effects on adult health?

  3. Existing Epidemiologic Studies • Most completed in last 5 years (35 published studies) • China, U.S., Brazil, Czech Republic, Canada, S. Korea, Taiwan, Lithuania, Croatia, Sweden, Mexico • Two recent review articles • Maisonet et al. 2004, Environmental Research, May;95(1):106-15 • Glinianaia et al. 2003, Epidemiology, 15:36-45

  4. Outcome Events Studied • Deaths • Intrauterine (28 weeks of gestation to birth) • neonatal (<28 days) • infant (< 1 year) • Low birth weight (LBW) • Weight at birth <2500g • Born LBW at term vs. preterm • Reduction in mean weight • Small for gestational age (SGA; <10th percentile of weight for gestational age) • Preterm births (<37 weeks of gestation)or • reduction of mean gestational age • Malformations (cardiac)

  5. Methodologic differences • Outcome categories • Term LBW, all LBW, SGA, preterm and/or LBW • Fetal, neonatal, infant deaths • Air pollutants • Area-wide averages (all monitoring stations) • Use monitor closest to maternal residency • Pollutants measured, mixtures, co-pollutants • Scaling of units for pollutants • Timing of exposure during most relevant pregnancy periods (varies by pollutant and outcome?) • Covariates included in model

  6. South Coast Air Basin • Large number of births (~half of all CA births, most in LA county) • Birth certificates are readily available • Network of government air monitoring stations • Nonattainment for PM10, PM2.5 and O3

  7. Summary of SoCAB Studies • Ritz and Yu (1999) evaluated association between CO exposures during 3rd trimester and risk of term LBW • Infants born 1989-1993 to women living in SoCAB • Exposure based on CO measurements at SCAQMD monitoring stations (n=18) • Focused on mothers who resided within 2 miles of a CO monitoring station (n=125,573) • For each child calculated last trimester average CO concentration using the ambient monitoring station within 2 miles

  8. Summary of SoCAB Studies • Logistic regression used to evaluate association between 3rd trimester CO and term LBW • Dichotomous outcome - <2,500g vs. 2,500g • Variables included in models • parity • sex of the infant • maternal age • maternal race/ethnicity • maternal educational attainment • interval since previous live birth <12 months • prenatal care • gestational age • transportation time to work (from census data)

  9. Summary of SoCAB Studies • Other risk factors not available on birth certificates • pre-pregnancy weight, weight gain, and height of mother • social factors (marital status?, occupational exposures to toxins?) • behavioral factors (e.g. smoking, caffeine use, alcohol consumption during pregnancy)

  10. Adjusted Odds Ratios (95%CI) for TermLBW 3rd trimester ambient CO levels 1989-1993, 18 monitoring stations in SoCAB All childrenHigher parity childrenYoung Women case N=2,809 case N=1,454 case N=420 non-case N=122,764 non-case N=73,687 non-case N=15,111 _____________________________________________________________________ CO level (ppm): <2.2 1.0 1.0 1.0 2.2 - <5.5 1.04 1.03 1.02 (0.96, 1.13) (0.92, 1.15) (0.83, 1.26) 5.5 1.22 1.33 1.54 (1.03, 1.44) (1.07, 1.65) (1.07, 2.22) _____________________________________________________

  11. Adjusted Odds Ratios (95%CI) for TermLBW 3rd trimester ambient CO levels 1989-1993, 6 monitoring stations in SoCAB w/ CO, NO2, O3, PM10 All childrenHigher parity childrenYoung Women case N=1,100 case N=584 case N=146 non-case N=46,921 non-case N=28,313 non-case N=5,918 _____________________________________________________________________ CO level (ppm): <2.2 1.0 1.0 1.0 2.2 - <5.5 1.10 1.24 1.30 (0.91, 1.32) (0.96, 1.60) (0.77, 2.20) 5.5 1.38 1.92 5.08 (0.86, 2.22) (1.02, 3.62) (1.77, 14.63) _____________________________________________________

  12. Summary of SoCAB Studies • Ritz et al. (2000) evaluated association between air pollution and preterm birth • Infants born 1989-1993 to women living in SoCAB (n=97,158) • Exposure assessment similar to Ritz and Yu (1999) • First month of pregnancy and weeks prior to birth

  13. Summary of SoCAB Studies • Logistic regression with dichotomous outcome (<37 wks vs. 37 wks completed gestation) • Controlled for: • maternal age, race, education; parity, interval since previous live birth, prenatal care, infant gender, previous LBW or preterm birth, smoking reported as “pregnancy complications”, season

  14. Odds ratio (and 95% CI) for Preterm BirthPer 50 ug/m3 increase in PM10 and 3 ppm increase in CO1989-1993 Crude Two Exposure Other Risk Other Risk Multipollutant OR Periods Factors Factors+Season Model __________________________________________________________________________________________ PM10 – All stations: 6 wks 1.20 1.18 1.15 1.15 1.19 (1.09-1.33) (1.07-1.31) (1.04-1.26) (1.03-1.29) (1.01-1.40) 1stmonth 1.16 1.13 1.09 1.09 1.12 (1.06-1.26) (1.04-1.24) (1.00-1.19) (0.99-1.20) (0.97-1.29) CO – All stations: 6 wks 1.12 1.13 1.06 1.04 1.05 (1.08-1.17) (1.08-1.17) (1.02-1.10) (0.99-1.10) (0.97-1.12) 1stmonth 1.04 1.05 1.01 1.04 1.03 (1.01-1.09) (1.01-1.09) (0.97-1.04) (0.99-1.09) (0.96-1.10) __________________________________________________________________________________________

  15. Summary of SoCAB studies • Ritz et al. (2002) evaluated association between air pollution and occurrence of birth defects • Used California Birth Defect Monitoring Program data to evaluate neonates/fetuses delivered in SoCAB during 1987-1993 • Evaluated 6 different common heart defects • Exposure based on SCAQMD monitoring station data during first 3 months of pregnancy for each infant

  16. CO and (isolated) Ventricle Septum Defects(multi-pollutant model)

  17. O3and Pulmonary artery and valve defects(multi-pollutant model)

  18. Results on Birth Defects • Risk of certain cardiac heart defects was three times greater at high exposure levels • Ventricle septum birth defects (CO) • Aortic and pulmonary artery and valve defects (O3) • Risks were observed in 2nd month of pregnancy when heart formation occurs

  19. Exposure Assessment • Based on concentrations measured at government air monitoring stations • May not account for differential exposure within neighborhoods due to proximity to sources • Women residing closer to freeways and major roadways may experience greater exposure • Pollutants released directly in motor vehicle exhaust • Pollutants formed adjacent to roadways

  20. Exposure Assessment • Existing measurement data indicate concentrations of motor vehicle exhaust pollutants (CO, NO2, primary particles) are: • Elevated near roadways and decline rapidly with distance • Correlated with traffic counts • Elevated inside and outside homes and schools located close to heavy traffic roadways

  21. Source: Ott, 1977

  22. IsCO a marker for traffic related pollution? Epidemiologic studies ignore potential spatial heterogeneity of vehicle-related air pollution when using exposure data from government air monitoring stations Y. Zhu and W. Hinds, UCLA Particle center

  23. Traffic Density How can we estimate traffic-related contributions using existing data for large areas? • Self-reported traffic density on street of residence • Residential distance to major roads/freeways • Measured traffic density on main roads near homes • Average traffic density in census block groups, tracts or wards • Distance weighted traffic density (DWTD) • Air dispersion models (e.g. Caline4)

  24. Summary of SoCAB Studies • Wilhelm and Ritz (2003) evaluated association between residential proximity to traffic and ABOs • For 1994-96, in 112 LA zip codes, we identified all • Term low birth weight (LBW) and preterm infants (n=31,653) and a random sample of controls (~same n) • Mapped residential birth addresses using GIS (ESRI StreetMap) • ~86% had electronic address data, of those ~91% could be mapped • Transferred Caltrans annual average daily traffic (AADT) count data for each year on to ESRI StreetMap

  25. Distance Weighted Traffic Density (DWTD) DWTD value calculated for each subject • for all streets within 750 ft. (228.6 m) radius of home • weighted traffic count on each street by distance from home to street (using a Gaussian distribution) • summed weighted counts for all streets within radius

  26. Summary of SoCAB Studies • Evaluated change in estimates when adjusting for following risk factors (based on birth records) • Level of prenatal care, maternal age, maternal race/ethnicity, maternal education, infant sex, parity, interval since last live birth, previous LBW or preterm infant, gestational age (for LBW), season, year of birth • Also evaluated change in estimates when adjusting for: • Background air pollution concentrations (annual averages) • One or more freeways within buffer • Census block-group level indicators of SES • Household income, per capita income, fraction of children in poverty, age of structure, median home value, median gross rent

  27. Association (RR point estimate, 95% CI) between Residential DWTD and Risk of Preterm Birth for infants born between 1994-1996 to mothers living in 112 zip codes located in LA County, CA DWTD percentile values are: <1,537, 1,537-5,338, 5,339-11,722, 11,723-24,711, ≥24,712.

  28. Low inversion layers trap pollutants in colder seasons

  29. Association (OR point estimate, 95% CI) between Residential DWTD and Risk of LBW and Preterm Birth for infants born between 1994-1996 to mothers living in 112 zip codes located in LA County, CA DWTD percentile values are: <1,537, 1,537-5,338, 5,339-11,722, 11,723-24,711, ≥24,712.

  30. Association (OR point estimate, 95% CI) between Residential DWTD and Risk of Term LBW for infants born between 1994-1996 to mothers living in 112 zip codes located in Los Angeles County, CA DWTD percentile values are: <1,524, 1,524-5,266, 5,267-11,568, 11,569-24,579, ≥24,580.

  31. DWTD Measure • Relatively crude exposure assessment approach • Does not take meteorology or motor vehicle emission rates into account • Can be applied to large population using existing data • Experimental support for exponential decay from roadways

  32. EPOS Survey • Nested case-control study of LA County births • LBW/Preterm children and term normal weight controls (targeted n=1000 case and 1000 controls over 1 year - 2003) • Randomly selected from birth certificates in 111 LA zip codes • Mothers interviewed by phone or completed a mail survey 3-7 months after births • Collected information on: • indoor air pollution sources • in-transit exposures • time-activity data • Individual level risk factors for LBW/preterm birth during pregnancy: • Smoking, alcohol, occupation, psychosocial stress

  33. EPOS Response Rates

  34. Data Linkages • Most studies based on existing data sources • Birth and death certificate information, CBDMP data • Residential addresses and SSN’s now available from state for birth certificates • Air pollution measurements from government monitors • Traffic data from Caltrans

  35. Major Questions • Adequacy of air pollution exposure assessment methods? • Reliance on existing monitoring networks • Potential intracommunity variation in pollutant concentrations • Time spent indoors and indoor sources • Reliance on birth certificate zip code or address • Residential and work mobility patterns for pregnant women • Which pollutants are important? • Associations reported for CO, NO2, TSP, SO2, PM10, PM2.5, PAHs • Identifying pollutants of concern and biological mechanisms of action

  36. Major Questions • Vulnerable pregnancy periods? • Associations reported most consistently for early or late pregnancy • Confounding due to unmeasured risk factors? • E.g., smoking, alcohol, diet, pregnancy weight gain • Susceptible subpopulations? • Importance of early pregnancy losses (unreported)?

  37. Discussion

  38. Adjusted Odds ratios (and 95% CI) for Term LBWAmbient CO levels at South Central LA station only, 1989-1993 1st Trim 2nd Trim 3rd Trim 3rd Trim 2-mile radius 2-mile radius 2-mile radius 5-mile radius _________________________________________________________________________________________________________ CO level: <50th 1.0 1.0 1.0 1.0 50-95th 0.87 1.02 1.06 1.07 (0.73-1.03) (0.85-1.20) (0.89-1.26) (0.99-1.16) >=95th 0.82 0.97 1.24 1.24 (0.54-1.24) (0.65-1.44) (0.87-1.77) (1.06-1.45) ________________________________________________________________________________________________________ 2 mile radius: case N=572, non-case N=23,533; 5 mile radius: case N=2,805, non-case N=94,160

  39. Adjusting for census block group level SES indicators changed association estimates minimally (maximum of 6% but mostly by 1-2%) • Stratification on median values of SES indicators suggested greater associations in lower SES areas *Results for highest vs. lowest DWTD quintile, adjusting for covariates, background pollutant concentrations (continuous) and census block group indicators of SES (continuous).

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