Ambient particulate matter and surrounding greenness in relation to sleep quality among pregnant women: A nationwide cohort study

Background

Particulate air pollution and residential greenness are associated with sleep quality in the general population; however, their influence on maternal sleep quality during pregnancy has not been assessed.

Objective

This cross-sectional study investigated the individual and interactive effects of exposure to particulate matter (PM) air pollution and residential greenness on sleep quality in pregnant women.

Methods

Pregnant women (n = 4933) enrolled in the Korean Children's Environmental Health Study with sleep quality information and residential address were included. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). The average concentrations of PM (PM2.5 and PM10) during pregnancy were estimated through land use regression, and residential greenness in a 1000 m buffer area around participants' residences was estimated using the Normalized Difference Vegetation Index (NDVI1000-m). Modified Poisson regression models were used to estimate the associations between PM and NDVI and poor sleep quality (PSQI >5) after controlling for a range of covariates. A four-way mediation analysis was conducted to examine the mediating effects of PM.

Results

After adjusting for confounders, each 10 μg/m3 increase in PM2.5 and PM10 exposure was associated with a higher risk of poor sleep quality (relative risk [RR]: 1.06; 95% confidence interval [CI]: 1.01, 1.11; and RR: 1.09; 95% CI: 1.06, 1.13, respectively), and each 0.1-unit increase in NDVI1000-m was associated with a lower risk of poor sleep quality (RR: 0.97; 95% CI: 0.95, 0.99). Mediation analysis showed that PM mediated approximately 37%-56% of the association between residential greenness and poor sleep quality.

Conclusions

This study identified a positive association between residential greenness and sleep quality. Furthermore, these associations are mediated by a reduction in exposure to particulate air pollution and highlight the link between green areas, air pollution control, and human health.

District-Level Risk Factors for COVID-19 Incidence and Mortality in Nepal

The recent global pandemic of the novel coronavirus disease 2019 (COVID-19) is affecting the entire population of Nepal, and the outcome of the epidemic varies from place to place. A district-level analysis was conducted to identify socio-demographic risk factors that drive the large variations in COVID-19 mortality and related health outcomes, as of 22 January 2021. Data on COVID-19 extracted from relevant reports and websites of the Ministry of Health and Population of Nepal, and the National Population and Housing Census and the Nepal Demographic and Health Survey were the main data sources for the district-level socio-demographic characteristics. We calculated the COVID-19 incidence, recovered cases, and deaths per 100,000 population, then estimated the associations with the risk factors using regression models. COVID-19 outcomes were positively associated with population density. A higher incidence of COVID-19 was associated with districts with a higher percentage of overcrowded households and without access to handwashing facilities. Adult literacy rate was negatively associated with the COVID-19 incidence. Increased mortality was significantly associated with a higher obesity prevalence in women and a higher smoking prevalence in men. Access to health care facilities reduced mortality. Population density was the most important driver behind the large variations in COVID-19 outcomes. This study identifies critical risk factors of COVID-19 outcomes, including population density, crowding, education, and hand hygiene, and these factors should be considered to address inequities in the burden of COVID-19 across districts.

Association between ambient air pollution and perceived stress in pregnant women

Air pollution may influence prenatal maternal stress, but research evidence is scarce. Using data from a prospective cohort study conducted on pregnant women (n = 2153), we explored the association between air pollution and perceived stress, which was assessed using the 14-item Perceived Stress Scale (PSS), among pregnant women. Average exposures to particulate matter with an aerodynamic diameter of < 2.5 µm (PM_2.5) or < 10 µm (PM₁₀), nitrogen dioxide (NO₂), and ozone (O₃) for each trimester and the entire pregnancy were estimated at maternal residential addresses using land-use regression models. Linear regression models were applied to estimate associations between PSS scores and exposures to each air pollutant. After adjustment for potential confounders, interquartile-range (IQR) increases in whole pregnancy exposures to PM_2.5, PM₁₀, and O₃ in the third trimester were associated with 0.37 (95% confidence interval [CI] 0.01, 0.74), 0.54 (95% CI 0.11, 0.97), and 0.30 (95% CI 0.07, 0.54) point increases in prenatal PSS scores, respectively. Furthermore, these associations were more evident in women with child-bearing age and a lower level of education. Also, the association between PSS scores and PM₁₀ was stronger in the spring. Our findings support the relationship between air pollution and prenatal maternal stress.

Association of ambient air pollution with depressive and anxiety symptoms in pregnant women: A prospective cohort study

BACKGROUND

Air pollution is associated with depressive and anxiety symptoms in the general population. However, this relationship among pregnant women remains largely unknown.

OBJECTIVE

To evaluate the association between pregnancy air pollution exposure and maternal depressive and anxiety symptoms during the third trimester assessed using the Center for Epidemiologic Studies-Depression and State-Trait Anxiety Inventory scales, respectively.

METHODS

We analyzed 1481 pregnant women from a cohort study in Seoul. Maternal exposure to particulate matter with an aerodynamic diameter <2.5 μm (PM_2.5) and <10 μm (PM₁₀), as well as to nitrogen dioxide (NO₂) and ozone (O₃) for each trimester and the entire pregnancy was assessed at participant's residential address by land use regression models. We estimated the relative risk (RR) and corresponding confidence interval (CI) of the depressive and anxiety symptoms associated with an interquartile range (IQR) increase in PM_2.5, PM₁₀, NO₂, and O₃ using modified Poisson regression.

RESULTS

In single-pollutant models, an IQR increase in PM_2.5, PM₁₀, and NO₂ during the second trimester was associated with an increased risk of depressive symptoms (PM_2.5 RR = 1.15, 95% CI: 1.04, 1.27; PM₁₀ RR = 1.13, 95% CI: 1.04, 1.23; NO₂ RR = 1.15, 95% CI: 1.03, 1.29) after adjusting for relevant covariates. Similarly, an IQR increase in O₃ during the third trimester was associated with an increased risk of depressive symptoms (RR = 1.09, 95% CI: 1.01, 1.18), while the IQR increase in O₃ during the first trimester was associated with a decreased risk (RR = 0.89, 95% CI: 0.82, 0.96). Exposure to PM_2.5, PM₁₀, and NO₂ during the second trimester was significantly associated with anxiety symptoms. The associations with PM_2.5 and O₃ in single-and multi-pollutant models were consistent.

CONCLUSIONS

Our findings indicate that increased levels of particulate matter, NO₂, and O₃ during pregnancy may elevate the risk of depression or anxiety in pregnant women.

Quantile regression analysis of the socioeconomic inequalities in air pollution and birth weight

BACKGROUND

An association between maternal exposure to air pollution and the birth weight distribution has been reported, but the extent to which this relationship varies according to socioeconomic status (SES) is unknown. This study examined the relationship using the data from a Korean birth cohort.

METHODS

Data for singleton births in Seoul from 2007 to 2017 (n = 1739) were analyzed. Maternal exposures to particulate matter with an aerodynamic diameter <10 µm (PM₁₀) and <2.5 µm (PM_2.5), as well as to nitrogen dioxide (NO₂) and ozone (O₃) for each trimester and the entire pregnancy were estimated using residential address, gestational age, and the birth date. The associations between the interquartile range (IQR) increases in pollutant concentrations and the changes in birth weight were examined using linear regression and quantile regression models. The socioeconomic disparities in the associations were investigated using a derived SES variable based on the composite of parental education and occupation. This SES variable was then interacted with the air pollutant.

RESULTS

In the gestational age-adjusted models, particulate air pollutants (PM₁₀ and PM_2.5) and O₃ were associated with birth weight decreases for the lower birth weight percentiles. For example, the decrease in mean birthweight per IQR increase in PM_2.5 during second trimester was -21.1 g (95% confidence interval (CI) = -41.8, -0.4), whereas the quantile-specific associations were: 10th percentile -27.0 g (95% CI = -46.6, -7.3); 50th percentile -22.2 g (95% CI = -39.6, -4.8); and 90th percentile -22.9 g (95% CI = -45.5, -0.2). Particulate air pollutants and O₃ showed a pattern of socioeconomic inequalities; the reduced birth weight was of greater magnitude for children from a low SES group.

CONCLUSIONS

Negative associations between particulate air pollutants and O₃ and birth weight were consistently greater at the lower quantiles of the birth weight distribution, especially in lower SES group.

Household air pollution and caste-ethnic differences in undernutrition among children in Nepal

This study investigated whether the association between household air pollution (HAP) and nutritional status (stunting, underweight, or wasting) among children differ by caste/ethnicity. Child anthropometry data for 9,914 children aged 0-59 months were analyzed linearly as Z scores and as dichotomous categories. Exposure to HAP was significantly associated with a decrease in child height-for-age and child weight-for-age, as well as with stunting and underweight. Children in low caste (Dalits) had higher prevalence of stunting (odds ratio [OR] = 1.21; 95% confidence intervals [CI] = 1.01, 1.44), underweight (OR = 1.47; 95% CI = 1.24, 1.75), and wasting (OR = 1.53; 95% CI = 1.21, 1.92) than those children in upper caste group. This association was modestly attenuated with adjustment for HAP. Exposure to HAP partly explained the caste-ethnic difference in undernutrition among children in Nepal.

Family-based case-control study of exposure to household humidifier disinfectants and risk of idiopathic interstitial pneumonia

Background

In Korea, several household humidifier disinfectants (HDs) were clinically confirmed to cause HD-associated lung injury (HDLI). Polyhexamethylene guanidine (PHMG) phosphate is the main ingredient of the HDs found to be associated with lung disease. However, the association of HDs with other interstitial lung disease including idiopathic interstitial pneumonia (IIP) is not clear. We examined the relationship between HD exposure and IIP in a family-based study.

Methods

This case-control study included 244 IIP cases and 244 family controls who lived with the IIP patients. The IIP cases were divided into two groups, HDLI and other IIP, and were matched to family controls based on age and gender. Information on exposure to HDs was obtained from a structured questionnaire and field investigations. Conditional logistic regression was used to estimate odds ratio (ORs) and their corresponding 95% confidence interval (CI), investigating the association of HD-related exposure characteristics with IIP risk.

Results

The risks of IIP increased two-fold or more in the highest compared with the lowest quartile of several HD use characteristics, including average total use hours per day, cumulative sleep hours, use of HD during sleep, and cumulative exposure level. In analyses separated by HDLI and other IIP, the risks of HDLI were associated with airborne HD concentrations (adjusted OR = 3.01, 95% CI = 1.34–6.76; Q₄ versus Q₁) and cumulative exposure level (adjusted OR = 3.57, 95% CI = 1.59–8.01; Q₄ versus Q₁), but this relationship was not significant in the patients with other IIP. In comparison between HDLI and other IIP, the odds ratios of average total use hours, cumulative use hours, and cumulative sleeps hours was higher for other IIP.

Conclusion

The use of household HDs is associated not only with HDLI but also with other IIP.

Depressive symptoms and risk of absence among workers in a manufacturing company: a 12-month follow-up study

Depression is a leading cause of reduced work ability and absence due to sickness. The objective of this study was to investigate how depressive symptoms are prospectively associated with subsequent absence, whether caused by illness or accidents, among manufacturing workers. This prospective study was conducted on 2,349 male and female employees that underwent a regular health examination at a university hospital. Depressive symptoms were measured at baseline using the Center for Epidemiologic Studies Depression (CES-D) Scale. Data on self-reported absence due to illness and accidents were obtained during a follow up of 1 yr. The incidences of sickness absence were 6.0% for men and 17.3% for women. Men and women with depressive symptoms (CES-D ≥16) were found to have higher odds of sickness absence during follow up (men: OR=4.06; 95% CI: 2.32-7.11; women: OR=1.75; 95% CI: 1.02-2.98), after adjustment for demographic and occupational factors. When depressive symptoms were divided into quartiles, significantly higher ORs of sickness absence were observed only among employees with the highest quartile of depressive symptoms. The study shows that depressive symptoms are a risk factor for future absence due to illness or accidents among manufacturing workers.

Air pollution exposure during pregnancy and ultrasound and birth measures of fetal growth: A prospective cohort study in Korea

Few studies have examined the effects of air pollution on fetal growth based on ultrasound measures during pregnancy. More data is needed to evaluate the windows of special vulnerability. Our aim was to investigate the association of ambient air pollution during pregnancy with fetal and neonatal characteristics in a cohort of Korean women. Maternal exposure to particulate matter with an aerodynamic diameter<10μm (PM₁₀) and nitrogen dioxide (NO₂) was estimated using land-use regression models based on residential address. The biparietal diameter (BPD), abdominal circumference (AC), femur length (FL), and estimated fetal weight (EFW) were evaluated via ultrasonography, and birth weight (BW), birth length (BL), and head circumference at birth (BHC) were obtained from medical records. The multiple linear regression model was used to adjust for confounders, and the mixed-effect model was used to evaluate longitudinal effect. The negative effects for NO₂ and PM₁₀ were estimated; in the adjusted analyses the decreases of BPD were -0.26mm (95% confidence interval [CI]=-0.41 to -0.11, with a 10μg/m³ increase) in the second trimester for NO₂, and -0.30mm (95% CI=-0.59 to -0.03, with a 10μg/m³ increase) in the third trimester for PM₁₀. Both NO₂ and PM₁₀ levels (10μg/m³) during third trimester were inversely associated with BHC, and NO₂ level was inversely associated with BL in all exposure windows. No significant associations for AC, FL, and EFW were observed. The longitudinal analyses showed inverse association of NO₂ exposure with head and length growth (P<0.001). Our findings suggest that ambient air pollution is associated with impaired fetal head size from mid-gestation onwards.

Associations between prenatal lead exposure and birth outcomes: Modification by sex and GSTM1/GSTT1 polymorphism

Maternal lead exposure is associated with poor birth outcomes. However, modifying effects of polymorphism in glutathione S-transferases (GST) gene and infant sex remain unexplored. Our aim was to evaluate whether associations between prenatal lead and birth outcomes differed by maternal GST genes and infant sex. Prospective data of 782 mother-child pairs from Mothers and Children's Environmental Health (MOCEH) study were used. The genotyping of GST-mu 1 (GSTM1) and theta-1 (GSTT1) polymorphisms was carried out using polymerase chain reaction. Multivariable linear regression was used to examine whether the association between blood lead (BPb) level and birth outcomes (birthweight, length, and head circumference) varied by maternal GST genes and sex. We did not find a statistically significant association between prenatal BPb levels and birth outcomes; in stratified analyses, the association between higher BPb level during early pregnancy and lower birthweight (β=-224 per square root increase in BPb; 95% confidence interval (CI): -426, -21; false discovery rate p=0.036) was significant in males of mothers with GSTM1 null. Results were similar for head circumference model (β=-0.78 per square root increase in BPb; 95% CI: -1.69, 0.14, p=0.095), but the level of significance was borderline. Head circumference model showed a significant three-way interaction among BPb during early pregnancy, GSTM1, and sex (p=0.046). For combined analysis with GSTM1 and GSTT1, GSTM1 null and GSTT1 present group showed a significant inverse association of BPb with birthweight and head circumference in males. Our findings of the most evident effects of BPb on the reduced birthweight and head circumference in male born to the mother with GSTM1 null may suggest a biological interaction among lead, GST genes and sex in detoxification process during fetal development.

Associations between Ambient Particulate Matter and Nitrogen Dioxide and Chronic Obstructive Pulmonary Diseases in Adults and Effect Modification by Demographic and Lifestyle Factors

This study was undertaken to investigate the associations between chronic exposure to particulate matter of medium aerodynamic diameter ≤10 or ≤2.5 µm (PM10 or PM2.5) and nitrogen dioxide (NO₂) levels and lung function and to examine a possible change in these relationships by demographic and lifestyle factors. Chronic obstructive pulmonary disease (COPD) was defined using the Global Initiative for COPD criteria (forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) of <70%). Associations of lung function and COPD with PM10 or PM2.5 or NO₂ were examined using linear and logistic regression analyses among 1264 Korean adults. The highest tertiles of PM2.5 (≥37.1 μg/m³) and NO₂ (≥53.8 μg/m³) exposure were significantly associated with COPD (highest versus lowest tertile of PM2.5: adjusted odds ratio (OR) = 1.79, 95% CI: 1.02-3.13; highest versus lowest tertile of NO₂: adjusted OR = 1.83, 95% CI: 1.04-3.21). A 10 μg/m³ increase in PM10 concentration was associated with a 1.85 L (95% CI -3.65 to -0.05) decrease in FEV1 and a 1.73 L (95% CI -3.35 to -0.12) decrease in FVC, with the strongest negative association among older people and those with less education. Reduced lung function was associated with PM2.5 exposure in subjects with no physical activity. This study provides evidence that exposure to ambient air pollution has adverse effects on lung function in adults.

Effects of traffic-related air pollution on susceptibility to infantile bronchiolitis and childhood asthma: A cohort study in Korea

OBJECTIVE

This study examined the role of exposure to traffic-related air pollution (TRAP) on susceptibility to asthma in children with past episodes of bronchiolitis.

METHODS

The baseline data included 2,627 school children aged 6-14 years who had participated in the longitudinal follow-up survey of the Children's Health and Environmental Research of Korea. Lifetime wheezing, past episodes of bronchiolitis, and doctor-diagnosed asthma were evaluated using an International Study of Asthma and Allergies in Childhood questionnaire. We used generalized linear regression with binomial distribution to calculate the relative risk (RR) between TRAP, assessed by proximity to a main road and the total length of roads, and asthma.

RESULTS

Compared with the subjects who had less than 100 m of road length within 200-m radius from their home, those with more than 500 m of road length had significantly increased odds for infantile bronchiolitis (adjusted OR [aOR]: 1.57, 95% confidence interval [CI]: 1.01-2.42). Positive exposure-response relationships were found between residential proximity to the main road and asthma (aOR: 1.79, 95% CI: 1.05-3.06; <75 m vs. >700 m from a main road, P for the trend = 0.02). Closer residential proximity to the main road (<75 m) and bronchiolitis combined increased the risks of newly diagnosed asthma (adjusted RR: 3.62, 95% CI: 1.07-12.26) compared with those without bronchiolitis and living ≥ 75 m away from the main road.

CONCLUSIONS

TRAP appeared to be associated with an increased asthma among children with bronchiolitis, indicating the importance of modifying effects of bronchiolitis in asthma pathogenesis.

Lung Cancer Risk and Residential Exposure to Air Pollution: A Korean Population-Based Case-Control Study

PURPOSE

To investigate the association between long-term exposure to ambient air pollution and lung cancer incidence in Koreans.

MATERIALS AND METHODS

This was a population-based case-control study covering 908 lung cancer patients and 908 controls selected from a random sample of people within each Korean province and matched according to age, sex, and smoking status. We developed land-use regression models to estimate annual residential exposure to particulate matter (PM₁₀) and nitrogen dioxide (NO₂) over a 20-year exposure period. Logistic regression was used to estimate odds ratios (ORs) and their corresponding 95% confidence intervals (CI).

RESULTS

Increases in lung cancer incidence (expressed as adjusted OR) were 1.09 (95% CI: 0.96-1.23) with a ten-unit increase in PM₁₀ (μg/m³) and 1.10 (95% CI: 1.00-1.22) with a ten-unit increase in NO₂ (ppb). Tendencies for stronger associations between air pollution and lung cancer incidence were noted among never smokers, among those with low fruit consumption, and among those with a higher education level. Air pollution was more strongly associated with squamous cell and small cell carcinomas than with adenocarcinoma of the lung.

CONCLUSION

This study provides evidence that PM10 and NO₂ contribute to lung cancer incidence in Korea.

Association of infant and young child feeding practices with under-nutrition: evidence from the Nepal Demographic and Health Survey

BACKGROUND

Childhood undernutrition remains a highly influential risk factor in terms of the global burden of disease. Increasing evidence links infant and young child feeding (IYCF) practices to undernutrition. However, the results are inconsistent, and more country-specific studies are needed.

OBJECTIVES

To determine the associations between IYCF practices and nutritional outcomes among children aged 0-23 months using a nationally representative dataset.

METHODS

The study used data from the 2011 Nepal Demographic and Health Survey, and the data were analysed for children aged 0-23.9 months who had corresponding data for the outcome variables of interest (n = 890). Multiple linear and logistic regressions were undertaken and adjusted for the complex design of the survey, controlling for child, maternal, household and community characteristics.

RESULTS

Of the 890 children included in the study, 83% received age-appropriate breastfeeding but only 48% were breastfed within 1 hour of birth. Exclusive breastfeeding under 6 months of age was associated with a higher weight-for-age Z-score (WAZ) and a lower probability of wasting, but the estimated effects were of borderline significance. A significant negative association was found between continued breastfeeding at 1 year and WAZ and weight-for-height Z-score (WHZ). Timely introduction of complementary feeding in children aged 6-8 months was associated with a higher WAZ [effect size (ES) 0.6, P < 0.01] and higher WHZ (ES 0.6, P < 0.05). Higher dietary diversity index (DDI) was associated with higher height-for-age Z-score (ES 0.1, P < 0.05 for each DDI point). Children who achieved minimum meal frequency had a higher WAZ (ES 0.3, P < 0.05).

CONCLUSION

This is the first study to relate the wide ranges of IYCF indicators with child nutritional outcomes in Nepal, and it underscores the need to improve age-appropriate complementary feeding practices with a sustained focus on exclusive breastfeeding to reduce undernutrition in infants and young children.

Increased prevalence of some birth defects in Korea, 2009-2010

Background

Birth defects are a leading cause of neonatal and infant mortality, and several studies have indicated an increase in the prevalence of birth defects; more recent investigations have suggested that the trends of some defects are increasing in rapidly industrialized areas. This study estimates the prevalence rate and types of birth defects in Korea.

Methods

This study used medical insurance benefit data of 403,250 infants aged less than one year from the National Health Insurance Corporation from seven metropolitan areas in Korea for 2009 and 2010.

Results

The prevalence rate of birth defects was 548.3 per 10,000 births (95 % CI: 541.1–555.6), 306.8 among boys and 241.5 among girls. Anomalies of the circulatory system (particularly septal defects) were the most common (180.8 per 10,000), followed by defects of the genitourinary tract (130.1 per 10,000) (particularly obstructive genitourinary and undescended testis), musculoskeletal system (105.7 per 10,000), digestive system (24.7 per 10,000), and central nervous system (15.6 per 10,000).

Conclusions

Relatively higher rates of some birth defects were found in the metropolitan areas. The high differences of birth prevalences for septal heart defects and undescended testis are probably due in part to progress in clinical management and more frequent prenatal diagnosis. Environmental exposure might play a critical role in the development of some birth defects. In attempting to describe the prevalence and spatio-temporal variations of birth defects in Korea, establishment of a registry system of birth defects and environmental surveillance are needed.

Association of infant and young child feeding practices with undernutrition in children: evidence from the Nepal Demographic and Health Survey

BACKGROUND

Childhood undernutrition remains a highly influential risk factor in terms of the global burden of disease. Increasing evidence links infant and young child feeding (IYCF) practices to undernutrition. However, the results are inconsistent, and more country-specific studies are needed.

OBJECTIVES

To determine the associations between IYCF practices and nutritional outcomes among children aged 0-23 months using a nationally representative dataset.

METHODS

The study used data from the 2011 Nepal Demographic and Health Survey, and the data were analysed for children aged 0-23.9 months who had corresponding data for the outcome variables of interest (n = 890). Multiple linear and logistic regressions were undertaken and adjusted for the complex design of the survey, controlling for child, maternal, household and community characteristics.

RESULTS

Of the 890 children included in the study, 83% received age-appropriate breastfeeding but only 48% were breastfed within 1 hour of birth. Exclusive breastfeeding under 6 months of age was associated with a higher weight-for-age Z-score (WAZ) and a lower probability of wasting, but the estimated effects were of borderline significance. A significant negative association was found between continued breastfeeding at 1 year and WAZ and weight-for-height Z-score (WHZ). Timely introduction of complementary feeding in children aged 6-8 months was associated with a higher WAZ [effect size (ES) 0.6, P < 0.01] and higher WHZ (ES 0.6, P < 0.05). Higher dietary diversity index (DDI) was associated with higher height-for-age Z-score (ES 0.1, P < 0.05 for each DDI point). Children who achieved minimum meal frequency had a higher WAZ (ES 0.3, P < 0.05).

CONCLUSION

This is the first study to relate the wide ranges of IYCF indicators with child nutritional outcomes in Nepal, and it underscores the need to improve age-appropriate complementary feeding practices with a sustained focus on exclusive breastfeeding to reduce undernutrition in infants and young children.

A meta-analysis of exposure to particulate matter and adverse birth outcomes

OBJECTIVES

The objective of this study was to conduct a systematic review to provide summarized evidence on the association between maternal exposure to particulate air pollution and birth weight (BW) and preterm birth (PTB) after taking into consideration the potential confounding effect of maternal smoking.

METHODS

We systematically searched all published cohort and case-control studies examining BW and PTB association with particulate matter (PM, less than or equal to 2.5μm and 10.0 μm in diameter, PM2.5 and PM10, respectively) from PubMed and Web of Science, from January 1980 to April 2015. We extracted coefficients for continuous BW and odds ratio (OR) for PTB from each individual study, and meta-analysis was used to combine the coefficient and OR of individual studies. The methodological quality of individual study was assessed using a standard protocol proposed by Downs and Black. Forty-four studies met the inclusion criteria.

RESULTS

In random effects meta-analyses, BW as a continuous outcome was negativelyassociated with 10 μg/m(3) increase in PM10 (-10.31 g; 95% confidence interval [CI], -13.57 to -3.13 g; I-squared=0%, p=0.947) and PM2.5 (-22.17 g; 95% CI, -37.93 to -6.41 g; I-squared=92.3%, p <0.001) exposure during entire pregnancy, adjusted for maternal smoking. A significantly increased risk of PTB per 10 μg/m(3) increase in PM10 (OR, 1.23; 95% CI, 1.04 to 1.41; I-squared=0%, p =0.977) and PM2.5 (OR, 1.14; 95% CI, 1.06 to 1.22; I-squared=92.5%, p <0.001) exposure during entire pregnancy was observed. Effect size of change in BW per 10 μg/m(3) increase in PM tended to report stronger associations after adjustment for maternal smoking.

CONCLUSIONS

While this systematic review supports an adverse impact of maternal exposure to particulate air pollution on birth outcomes, variation in effects by exposure period and sources of heterogeneity between studies should be further explored.

Water accessibility and child health: use of the leave-out strategy of instruments

This paper investigates the leave-out strategy of instruments by using the leave-out community ratio of household access to in-yard water sources and community water infrastructure as instruments for hours in fetching water time, and the data on disease symptoms. The results show that community-level access to clean water is significantly associated with both water-relevant and irrelevant disease symptoms, which suggests that the correlation between community-level access to clean water and child health is at least partially due to endogenous project placement potentially with respect to unobserved community wealth. The paper concludes that the OLS estimates have a potential endogeneity bias problem and that IV estimates under this strategy is subject to endogenous project placement and is not valid. A policy implication of this study is that careful attention should be paid to both self-selection and endogenous project placement in studying the effect of water accessibility on child health.