Birth certificate in california

ABBREVIATIONS. CO, carbon monoxide; TSP, total suspended particulate; P[M.sub.10], particulate matter measuring less than 10 [micro]m; P[M.sub.2.5], particulate matter measuring less than 2.5 [micro]m; SGA, small for gestational age; CI, confidence interval; AOR, adjusted odds ratio.

Evidence from the United States and elsewhere suggests that a variety of poor perinatal outcomes may be associated with exposure to poor air quality. (1-12) In Southern California, the risks for birth defects, preterm delivery, and low birth weight (birth weight <2500 g) have been found to be higher with higher levels of air pollution, mostly associated with particulate-matter air pollution and carbon monoxide (CO). (2-4) In the northeastern United States, however, associations between trimester exposures to various pollutants and term low birth weight were inconsistent among trimester of exposure, maternal race, and pollutant. (5) International studies have reported that Polish infants who were exposed to high levels of fine particles had lower birth weights than their counterparts with lower exposure levels (7); Beijing mothers living in residential areas with higher exposure to sulfur dioxide and total suspended particulates (TSPs) during the third trimester were at increased risk for delivering a low birth weight infants and delivering prematurely, (9) and first-trimester exposure to higher levels of pollutants increased the risk for low birth weight among term infants in Seoul. (10) A recent study in Sao Paulo, Brazil, found impaired fetal growth among infants with relatively high exposure to CO in the first trimester. (11) A study of data from the Czech Republic found that infant intrauterine growth retardation among full-term infants was more common for mothers who were exposed to high levels of particulate matter during the first trimester, although not later during pregnancy (12); additional work from the Czech Republic led to the conclusion that some of this association could be attributed to the polycyclic aromatic hydrocarbons, bound to small particles. (13) After delivery, higher levels of air pollution may increase the risk for infant mortality. (14-17) Although socioeconomic and racial disparities in infant health outcomes are well documented and disadvantaged groups may be exposed to higher levels of pollution, (18) the potential confounding effects of demographic factors on the association between infant health and air pollution are not well understood. A systematic review of studies of particulate air pollution and infant health concluded that the evidence is consistent with a possible effect of air pollution on birth weight but also could be consistent with no effect as the studies included in review are primarily from outside the United States and show different associations for exposures during different periods of pregnancy as well as between population subgroups. (1)

Many previous studies of particulate-matter air pollution and birth outcomes have primarily focused on particulate matter measuring less than 10 [micro]m (P[M.sub.10]) or TSP. (1) Both P[M.sub.10] and TSP have been shown to cause a range of other health effects, including mortality and morbidity from cardiovascular- and respiratory-related causes. (19) Studies in the past several years indicate that it may be the smaller particles, measuring less than 2.5 [micro]m (P[M.sub.2.5]), that are more likely to be associated with these health effects. (19-21) These particles are considered potentially more toxic as the majority of them are from combustion sources, such as cars, utilities, and wood burning, rather than crustal sources, such as road dust and agricultural fields. A study from the Czech Republic found similar associations between particulates and birth weight using both P[M.sub.2.5] and P[M.sub.10] (12); however, the components of particulates in the Czech Republic, including P[M.sub.10] and P[M.sub.2.5], may differ from those of the United States. In addition, pollution levels are lower in the United States than in the Czech Republic. Particulate matter may have systemic influences on pregnant women, including placental development or transplacental effects, that may result in adverse birth outcomes (22) or indirectly by influencing the health of the mother. Monitoring networks for P[M.sub.2.5] have been established in the United States since 1999, which provides an opportunity to study the effects of this component of particulate-matter air pollution on health.

To assess the relationship between fine particles and perinatal health, we used the recently available monitoring data in California for P[M.sub.2.5] to examine the relationship between fine particles, as measured by P[M.sub.2.5], and birth weight among full-term infants who were delivered in 2000 and to assess whether CO is a potential confounder or contributor. Additional analysis examined the association between CO and birth weight; CO was found to be associated with birth weight in a previous study of California mothers (3) and could potentially confound the relationship between P[M.sub.2.5] and birth weight. For our study, we calculated average pollution exposure using monitoring data from all monitors within 5 miles of the mother's residence. For each birth, we calculated averages for the time periods corresponding to the 9 months of pregnancy as well as for each trimester; trimester-specific exposures were examined to identify potentially critical times during pregnancy when particulates may affect birth weight. We used 2 outcome measures: (1) birth weight, measured continuously, and (2) small for gestational age (SGA), a classification that separates infants who are below and above the 10th percentile of birth weight for gestational age. We limited the study to infants who were delivered at 40 weeks' gestation to investigate specifically the relationship between pollution and intrauterine growth, without the potentially confounding effects of pregnancy duration on birth weight; limiting the study to 1 gestational week also reduces the potential for bias associated with the calculation of the exposure over the different lengths of pregnancy.

METHODS

Exposure Measurements

Pollution monitoring data for 1999 and 2000 were obtained from the California Air Resources Board for P[M.sub.2.5] and CO (California Air Quality Data, 2003, unpublished data). P[M.sub.2.5] was measured every 6 days, for example, twice in a 12-day period, and CO was monitored each day. We used the 24-hour average CO value, which was highly correlated with the other calculated CO measures, including the 8-hour maximum average CO value. PM monitors with fewer than 45 P[M.sub.2.5] measurements over 1 year were not considered representative of the entire exposure period and were excluded. CO monitors specifically designed to collect background concentrations or source-specific concentrations of CO were excluded. No P[M.sub.2.5] monitors were specified as background or source oriented.

Before we calculated the pregnancy-specific exposure variables, we trimmed the top and bottom 5% of the annual measurements from the set of monitoring values to better approximate average exposures without the influence of extreme measurements. (23) For each birth, measurements obtained from monitors within 5 miles of the mother's residence were used for the exposure calculations. Distances between maternal residence at the time of delivery and each of the P[M.sub.2.5] and CO monitors were computed using the corresponding latitudes and longitudes; although we used an equation for the distance incorporating the curvature of the earth, because we limited our study sample to mothers who lived within 5 miles of a monitor, the actual distances calculated were nearly identical to the usual Cartesian distance between 2 points. When >1 monitor was available within 5 miles, an average of the measurements from the corresponding monitors was calculated. In turn, 9-month and trimester-specific P[M.sub.2.5] and CO variables were calculated by using the measurements and the dates of the measurements collected from the identified monitors within 5 miles of each mother's residence. For example, for an infant who was born at the beginning of December, third-trimester exposure would be calculated from the measurements obtained from the 27th week of gestation in the beginning of September until the date of birth in early December; 9-month exposure measures were calculated using all measurements during pregnancy. The median number of measurements used to calculate the 9-month P[M.sub.2.5] exposure variable was 82, with an interquartile range of 69 to 143 measurements; for the 9-month CO variable, the median number of measurements was 264, with an interquartile range of 250 to 274. Quartiles of exposure for P[M.sub.2.5] and CO were defined using the observed distributions in the study population.

Study Population