Ozone and Preterm Birth in Women With Gestational Diabetes
Prenatal exposure to ambient air pollutants might cause adverse birth outcomes; however, there have been few studies in which the association between air pollution and preterm birth was examined after stratifying by pregnancy complications. We conducted a population-based case-control study of 1,510,064 singleton births from the Taiwanese birth registry during 2001–2007. Of the total of 1,510,064 births, we designated all 86,224 preterm births as the case group and then randomly selected an additional 344,896 from the remaining births (equivalent to 4 full-term births for every 1 preterm birth) as the control sample. We used an inverse distance weighting approach to calculate an average exposure parameter for air pollutants. The adjusted odds ratio for preterm birth per 10-ppb increase in ozone was 1.12 (95% confidence interval: 1.01, 1.23) for women with gestational diabetes mellitus who were exposed in the third trimester and 1.02 (95% confidence interval: 1.01, 1.03) for women without gestational diabetes (P for interaction <0.001). These findings suggest that exposure to ozone in pregnancy is associated with an increased risk of preterm birth, particularly for women who have gestational diabetes mellitus.
Preterm birth is a significant perinatal health problem across the globe, and it is associated with an increased risk of neonatal morbidity and mortality compared with full-term birth. In Taiwan, this is especially important because of the declining crude birth rate (from 15.52% to 10.08% from 1992 to 2012). The prevalence of preterm births worldwide is 9.6%, and the average in Taiwan is 9.2%. There is growing evidence that ambient air pollution might contribute to health problems, such as premature death, adverse reproductive outcomes, and respiratory and cardiovascular diseases, particularly in pregnant women and newborn children. In the past decade, the ambient air concentrations of most pollutants have decreased in Taiwan. The exception is ozone, the concentration of which has gradually increased. Most previous studies of the links between air pollution and preterm births have explored the association of traffic-related pollutants or particulate matter with preterm birth rather than ozone. In an animal experiment, Kavlock et al. reported that exposure to ozone during late gestation in rats led to abnormal reproductive function. However, it is still unclear which biological mechanisms operate during ozone exposure in humans. Numerous epidemiologic studies have provided evidence that ambient air pollution plays an important role in preterm birth. The evidence of an association between ozone and preterm birth, however, has been inconsistent. These inconsistent results may be due to differences in the prevalence of conditions that modify the association or in the average concentrations of ozone in the areas studied.
In addition to adverse birth outcomes, the association between pregnancy complications and air pollution has been examined in previous studies. However, to our knowledge, no study has yet explored the association between air pollution and pregnancy complications and the potential effect of that association on the risk of preterm birth. We conducted a population-based case-control study to assess the association between air pollution and preterm birth in single-pollutant and multipollutant models. We also investigated the link between exposure to air pollution and the risk of preterm birth in the subgroups of pregnant women who experienced pregnancy complications.
Abstract and Introduction
Abstract
Prenatal exposure to ambient air pollutants might cause adverse birth outcomes; however, there have been few studies in which the association between air pollution and preterm birth was examined after stratifying by pregnancy complications. We conducted a population-based case-control study of 1,510,064 singleton births from the Taiwanese birth registry during 2001–2007. Of the total of 1,510,064 births, we designated all 86,224 preterm births as the case group and then randomly selected an additional 344,896 from the remaining births (equivalent to 4 full-term births for every 1 preterm birth) as the control sample. We used an inverse distance weighting approach to calculate an average exposure parameter for air pollutants. The adjusted odds ratio for preterm birth per 10-ppb increase in ozone was 1.12 (95% confidence interval: 1.01, 1.23) for women with gestational diabetes mellitus who were exposed in the third trimester and 1.02 (95% confidence interval: 1.01, 1.03) for women without gestational diabetes (P for interaction <0.001). These findings suggest that exposure to ozone in pregnancy is associated with an increased risk of preterm birth, particularly for women who have gestational diabetes mellitus.
Introduction
Preterm birth is a significant perinatal health problem across the globe, and it is associated with an increased risk of neonatal morbidity and mortality compared with full-term birth. In Taiwan, this is especially important because of the declining crude birth rate (from 15.52% to 10.08% from 1992 to 2012). The prevalence of preterm births worldwide is 9.6%, and the average in Taiwan is 9.2%. There is growing evidence that ambient air pollution might contribute to health problems, such as premature death, adverse reproductive outcomes, and respiratory and cardiovascular diseases, particularly in pregnant women and newborn children. In the past decade, the ambient air concentrations of most pollutants have decreased in Taiwan. The exception is ozone, the concentration of which has gradually increased. Most previous studies of the links between air pollution and preterm births have explored the association of traffic-related pollutants or particulate matter with preterm birth rather than ozone. In an animal experiment, Kavlock et al. reported that exposure to ozone during late gestation in rats led to abnormal reproductive function. However, it is still unclear which biological mechanisms operate during ozone exposure in humans. Numerous epidemiologic studies have provided evidence that ambient air pollution plays an important role in preterm birth. The evidence of an association between ozone and preterm birth, however, has been inconsistent. These inconsistent results may be due to differences in the prevalence of conditions that modify the association or in the average concentrations of ozone in the areas studied.
In addition to adverse birth outcomes, the association between pregnancy complications and air pollution has been examined in previous studies. However, to our knowledge, no study has yet explored the association between air pollution and pregnancy complications and the potential effect of that association on the risk of preterm birth. We conducted a population-based case-control study to assess the association between air pollution and preterm birth in single-pollutant and multipollutant models. We also investigated the link between exposure to air pollution and the risk of preterm birth in the subgroups of pregnant women who experienced pregnancy complications.
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