The association between ambient air pollution and selected adverse pregnancy outcomes in China: A systematic review

Combined effects of ambient air pollution and home environmental factors on low birth weight

BACKGROUND

Low birth weight (LBW) remains a major public health problem worldwide, yet its crucial environmental risk factors are still unclear.

OBJECTIVE

To examine the association between LBW (term and preterm LBW) and prenatal exposure to ambient air pollution and home environmental factors as well as their combination, in order to identify critical time window for exposure and key outdoor and indoor factors in LBW development.

METHODS

A cohort study of 3509 preschool children was performed in Changsha, China during the period 2011-2012. A questionnaire was conducted to survey each child's birth outcome and each mother's exposure to home environmental factors including parental smoking, new furniture, redecoration, mold/damp stains, window pane condensation, and household pets during pregnancy. Maternal exposure to inhalable particulate matter (PM₁₀), industrial air pollutant (SO₂), and traffic air pollutant (NO₂) was estimated during different time windows of gestation, including conception month, three trimesters, birth month, and whole gestation. Associations of term and preterm LBW with ambient air pollutants and home environmental factors were assessed by multiple logistic regression models in terms of odds ratio (OR) with 95% confidence interval (CI).

RESULTS

Term LBW (TLBW) was significantly associated with exposure to ambient PM₁₀ during pregnancy, with OR (95% CI) = 1.47 (1.00-2.14) for per IQR increase after adjustment for the covariates and home environmental factors. Specifically, we identified the significant association in early phase of pregnancy including conception month (1.90, 1.09-3.30) and the first trimester (1.72, 1.10-2.69). We further found that TLBW was significantly related with parental smoking at home, OR (95% CI) = 2.17 (1.09-4.33). However, no association was observed for preterm LBW (PLBW). The TLBW risk of ambient air pollution and home environmental factors was independent each other and hence the combined exposure to ambient PM₁₀ and indoor parental smoking caused the highest risk. Sensitivity analysis suggested that foetus with younger mothers were significantly more susceptible to risk of indoor parental smoking, while those with smaller house and cockroaches were more sensitive to risk of outdoor PM₁₀ exposure.

CONCLUSION

Prenatal exposure to combined outdoor and indoor air pollution, particularly in critical window(s) during early pregnancy, significantly increases the risk of term LBW.

Effect of PM2.5 on macrosomia in China: A nationwide prospective cohort study

BACKGROUND

Macrosomia is associated with both neonatal complications and adult diseases (obesity, diabetes mellitus, etc.). Previous studies have reported maternal exposure to PM2.5 might influence metabolism and fetal development and cause adverse pregnancy outcomes. Studies conducted in areas with low PM2.5 concentration have found relationship between gestational PM2.5 exposure and birth weight. However, the impact of air pollution on macrosomia has not been studied, especially in highly polluted areas.

OBJECTIVE

To evaluate the association between fine particulate matter (PM2.5) exposure during pregnancy and the risk of macrosomia.

METHODS

Data from preconception health examination and prenatal and postnatal records were collected from 1 January 2010 to 31 December 2012 in the National Free Preconception Health Examination Project. Monthly mean of PM2.5 concentration during pregnancy was estimated from satellite data using an ensemble machine learning model. A newborn with birth weight above 4000 g was defined as macrosomia. Logistic regression models were used to examine the association between maternal exposure to PM2.5 and the risk of macrosomia, after adjusting for maternal age, pre-pregnancy body mass index, parity, neonatal sex, duration of gestation, seasonality, educational level, smoking and drinking habits, past history of diabetes mellitus and hypertension, and family history of diabetes mellitus. Restricted cubic spline models were used to evaluate the dose-response relationship between the risk of macrosomia and PM2.5 concentration.

RESULTS

Of 177 841 singleton nonlow birth weight newborns included, 14 598 (8.2%) had macrosomia. The mean PM2.5 concentrations were 70.7, 71.5, and 80.9 μg/m³ in the first, second, and third trimesters. In full-adjusted logistic regression models, significant associations were found between increased risk of macrosomia and every 10 μg/m³ increase of PM2.5 concentration over the first (odds ratio [OR]: 1.045; 95% CI, 1.037-1.052), second (OR: 1.035; 95% CI, 1.028-1.043), and third (OR: 1.033; 95% CI, 1.026-1.039) trimesters. There was a nonlinear does-response association between PM2.5 concentration and the risk of macrosomia.

CONCLUSIONS

Maternal exposure to PM2.5 during pregnancy was associated with an increased risk of macrosomia in China.

Risk of particulate matter on birth outcomes in relation to maternal socio-economic factors: a systematic review

A growing number of studies provide evidence of an association between exposure to maternal air pollution during pregnancy and adverse birth outcomes including low birth weight and preterm birth. Prevention of these health effects of air pollution is critical to reducing the adverse infant outcomes, which can have impacts throughout the life course. However, there is no consensus on whether the association between air pollution exposure and birth outcomes varies by maternal risk factors including demographic characteristics and socio-economic status. Such information is vital to understand potential environmental health disparities. Our search found 859 unique studies, of which 45 studies met our inclusion criteria (Jan. 2000- July. 2019). We systematically reviewed the 45 identified epidemiologic studies and summarized the results on effect modifications by maternal race/ethnicity, educational attainment, income, and area-level socio-economic status. We considered adverse birth outcomes of preterm birth, low birth weight, small for gestational age (SGA), and stillbirth. Suggestive evidence of higher risk of particulate matter in infants of African-American/black mothers than infants of other women was found for preterm birth and low birth weight. We found weak evidence that particulate matter risk was higher for infants of mothers with lower educational attainment for preterm birth and low birth weight. Due to the small study numbers, we were unable to conclude whether effect modification is present for income, occupation, and area-level socio-economic status, and additional research is needed. Furthermore, adverse birth outcomes such as SGA and stillbirth need more study to understand potential environmental justice issues regarding the impact of particulate matter exposure during pregnancy on birth outcomes.

Particulate matter exposure shapes DNA methylation through the lifespan

Exposure to airborne particulate matter (PM) has been associated with detrimental health effects. DNA methylation represents the most well-studied epigenetic factor among the possible mechanisms underlying this association. Interestingly, changes of DNA methylation in response to environmental stimuli are being considered for their role in the pathogenic mechanism, but also as mediators of the body adaptation to air pollutants.Several studies have evaluated both global and gene-specific methylation in relation to PM exposure in different clinical conditions and life stages. The purpose of the present literature review is to evaluate the most relevant and recent studies in the field in order to analyze the available evidences on long- and short-term PM exposure and DNA methylation changes, with a particular focus on the different life stages when the alteration occurs. PM exposure modulates DNA methylation affecting several biological mechanisms with marked effects on health, especially during susceptible life stages such as pregnancy, childhood, and the older age.Although many cross-sectional investigations have been conducted so far, only a limited number of prospective studies have explored the potential role of DNA methylation. Future studies are needed in order to evaluate whether these changes might be reverted.

Estimating the acute effects of ambient ozone pollution on the premature rupture of membranes in Xinxiang, China

While increasing evidence suggests that ozone (O₃) exposure is associated with adverse birth outcomes, only one study has focused on its impact on the premature rupture of membranes (PROM). Therefore, we thus examined the effect of O₃ on PROM in Xinxiang, China, using an over-dispersed Poisson generalized additive model. Several confounding factors, including meteorological factors, temporal trends, the day of the week, and public holidays, were considered in the model. We identified a total of 3255 instances of PROM from January 1, 2015 to December 31, 2017, and there was a significant association between the daily maximum 8-h mean concentrations (O_3-8h) and PROM. Each 10 μg/m³ increase in the 3-day average concentration (lag02) of O_3-8h corresponded to an increment in PROM of 5.42% (95% CI: 1.45-9.39%). Although the results of the stratified analyses were insignificant, a few trending results were observed: stronger associations between O₃ and PROM would occur in women with advanced age (≥35) or during the warm season than those in younger women (<35) or during the cool season. Our study indicates that O₃ exposure is an important risk factor of PROM and should be considered in its prevention and control in the study area.

Association of ambient air pollutants and birth weight in Ningbo, 2015-2017

Previous studies have suggested a change of birth weight linked with elevated ambient air pollutant concentrations during the pregnancy. However, investigations of the influence of higher pollutant levels on birth weight change are limited. The goal of this study is to evaluate whether the air pollution of Ningbo is associated with birth weight, and which trimester could be a window period for maternal exposure to air pollution. A total of 170,008 live births were selected in the Ningbo city of Zhejiang, China, from 2015 to 2017. We estimated the association between the decreased birth weight and the increased air pollutant concentrations in the three trimesters and full gestation. The effects of interaction among pollutants were identified using a co-pollutant adjustment model. An interquartile range increases in PM_2.5 (10.55 μg/m³), SO₂(4.6 μg/m³), CO (125.59 μg/m³), and O₃ (14.54 μg/m³) concentrations during the entire gestation were associated with 3.65 g (95% confidence interval: -6.02 g, -1.29 g), 5.02 g (-6.89 g, -3.14 g), 2.64 g (-4.65 g, -0.63 g) and 2.9 g (-4.8 g, 1 g) decreases, respectively, in birth weight. With each interquartile range increment in NO₂ concentration was associated with an 8.05 g (6.24 g, 9.85 g) increase in birth weight. In the first trimester, only the PM_2.5 exposure seemed to be associated with the greatest decline in birth weight. After adjustment for co-pollutant, both PM_2.5 and SO₂ were still associated with birth weight, except for CO for O₃ adjustment, O₃ for SO₂ adjustment, and O₃ for NO₂ adjustment. Maternal exposure to air pollution may be associated with a decrease of birth weight, but the contribution of various pollutants is necessary to verify by future research.

Air pollution, ambient temperature, green space and preterm birth

PURPOSE OF REVIEW

Preterm birth is the leading cause of global child mortality, and survivors are at increased risk of multiple morbidities that can continue into adulthood. Recent studies have suggested that maternal exposure to air pollution and high and low ambient temperatures may increase the risk of preterm birth, whereas proximity to green space may decrease it. This review summarizes these findings and suggests avenues for further research.

RECENT FINDINGS

Particulate matter may be associated with an increased risk of preterm birth, but the magnitude of the effect remains unclear. Heat and cold likely increase the risk of preterm birth, with stronger evidence for heat. The first and third trimesters may be sensitive periods for exposure to both temperature and particulate matter, but the underlying biological mechanisms are incompletely understood. Context-appropriate green space can substantially reduce particulate matter levels and mitigate urban heat islands.

SUMMARY

In a warming, urbanizing world, exposure to unusual temperatures and elevated particulate matter levels represent an increasing risk for pregnant women. Green infrastructure might help mitigate this risk, but further research is needed to confirm its effects in complex urban environments and evaluate the contribution of both indoor and outdoor particulate matter and air temperature to personal exposure and preterm birth.

Impact of air pollution on low birth weight in Spain: An approach to a National Level Study

BACKGROUND

According to the WHO, low birth weight (<2500 gr) is a primary maternal health indicator as the cause of multiple morbi-mortality in the short and long-term. It is known that air pollution from road traffic (PM₁₀, NO₂) and O₃ have an important impact on low birth weight (LBW), but there are few studies of this topic in Spain. The objective of this study is to determine the possible exposure windows in the gestational period in which there is greater susceptibility to urban air pollution and to quantify the relative risks (RR) and population attributable risks (PAR) of low birth weight associated with pollutant concentrations in Spain.

METHODS

We calculated the weekly average births with low birth weight (ICD-10: P07.0-P07.1) for each Spanish province for the period 2001-2009, using the average weekly concentrations of PM₁₀, NO₂ and O₃, measured in the capital cities of the provinces. The estimation of RR and PAR were carried out using generalized linear models with link Poisson, controlling for the trend, seasonality and auto-regressive character of the series and for the influence of temperature during periods of heat waves and/or cold. Finally, a meta-analysis was used to estimate the global RR and PAR based on the RR obtained for each of the provinces.

RESULTS

The RR for the whole of Spain is 1.104 (CI95%: 1.072, 1.138) for the association between LBW and PM₁₀, and 1.091 (CI95%: 1.059, 1.124) for the association between NO₂ and LBW. Our results suggest that 5% of low birth weight births in the case of PM₁₀ and 8% in the case of NO₂ could have been avoided with a reduction of 10 μg/m³ in the concentrations of these pollutants.

CONCLUSIONS

The impact of the results obtained- with 6105 cases attributable to PM₁₀ and up to 9385 cases attributable to NO₂ in a period of 9 study years- suggest the need to design structural and awareness public health measures to reduce air pollution in Spain.

Household renovation before and during pregnancy in relation to preterm birth and low birthweight in China

From October 2010 to April 2012, we conducted a cross-sectional study of associations between household environments and childhood health among preschool children in eight Chinese cities. Here, we analyze associations of early household renovation with preterm birth (PTB), low birthweight (LBW), term low birthweight (Term-LBW), and small for gestational age (SGA). Parents responded to questions about household renovation and their children's gestational age and birthweight. In the multivariate logistic regression analyses, household renovation in the year before pregnancy was significantly associated with LBW (sample size: N = 25 813; adjusted odds ratio (OR) with 95% confidence intervals (CIs): 1.23, 1.01-1.50) and Term-LBW (N = 24 823; 1.29, 1.01-1.67). Household renovation during pregnancy was significantly associated with PTB (N = 25 202; 1.28, 1.01-1.69). These significant associations were also found in the two-level (city-child) logistic regression analyses and in the sensitivity analyses among 21 009 children with complete data in all studied variates. Stronger associations were found in certain subgroups. Our findings indicate that household renovation within one year before pregnancy might be a risk factor for LBW and Term-LBW, while household renovation during pregnancy could be a risk factor for PTB.

Pollution and children's health

FINDINGS

The Lancet Commission on Pollution and Health found that pollution - air, water, soil, and chemical pollution - was responsible in 2016 for 940,000 deaths in children worldwide, two-thirds of them in children under the age of 5. Pollution is inequitably distributed, and the overwhelming majority of pollution-related deaths in children occurred in low- and middle-income countries (LMICs). Most were due to respiratory and gastrointestinal diseases caused by polluted air and water. Pollution is linked also to multiple non-communicable diseases (NCDs) in children including low birth weight, asthma, cancer and neurodevelopmental disorders, and these diseases are on the rise. The full impact of pollution, especially chemical pollution on the global burden of pediatric disease is not yet known, but almost certainly is undercounted because patterns of chemical exposure are not well charted and the potential toxicity of many chemical pollutants has not been characterized. The list of pediatric NCDs attributed to pollution will likely expand as the health effects of newer chemical pollutants are better defined and additional associations between pollution and disease are discovered.

CONCLUSION

Pollution prevention presents a major, largely unexploited opportunity to improve children's health and prevent NCDs, especially in LMICs. Failure to incorporate pollution prevention into NCD control programs is a major missed opportunity for disease prevention.

Acute and chronic effects of ambient fine particulate matter on preterm births in Beijing, China: A time-series model

Accumulating evidence suggests that short- and long-term exposure to ambient fine particulate matter ≤ 2.5 μm (PM_2.5) during pregnancy is associated with preterm births, yet the results are inconsistent, and the shape of the exposure-response curve is unclear, partially due to the limited studies conducted in areas with high air pollution. Our study evaluated the association between ambient PM_2.5 concentration and preterm births in Beijing, China. Daily preterm birth data were collected from a hospital in Beijing during 2006 to 2013; a time-series of daily PM_2.5 concentrations during the same period is assembled with measured data at three monitoring sites in Beijing. An extension of the Poisson regression and a time-series model were applied to simultaneously estimate the acute and chronic effects of exposure to PM_2.5, with mutual adjustment for short- and long-term exposure as well as for confounders. During the study period, the PM_2.5 concentration was 70.4 ± 60.6 μg/m³ and was found to be associated with an increased risk of preterm birth. In the study cohort, a 0.52% (95% confidence interval, CI: 0.09%, 0.96%) and 3.13% (95%CI: 1.92%, 4.35%) increase in preterm births was estimated for each 10-μg/m³ increase in short- and long-term exposure, respectively. This association was significantly modified by season (p < 0.05). With mutual adjustments for short- and long-term exposure, a more robust association (3.16%, 95% CI: 1.95%, 4.39%; per 10-μg/m³ increment in PM_2.5) was observed for chronic effects. The exposure-response relationships for both short- and long-term exposure were linear, without a threshold, over the relatively low exposure range and flattened out at higher concentration levels. The maximum effect for long-term exposure to PM_2.5 (33.6%) was much greater than that for short-term exposure (19.9%). These findings indicate that air quality improvements over a long period could yield significant health benefits.

Nitrogen dioxide air pollution and preterm birth in Shanghai, China

BACKGROUND

Nitrogen dioxide (NO₂) is a typical indicator of traffic-related air pollution, and few studies with exposure assessment of high resolution have been conducted to explore its association with preterm birth in China.

OBJECTIVES

To investigate the association between NO₂ exposure based on a land use regression (LUR) model and preterm birth in Shanghai, China.

METHODS

A retrospective cohort study was performed among 25,493 singleton pregnancies in a major maternity hospital in Shanghai, China, from 2014 to 2015. A temporally adjusted LUR model was used to predict the prenatal exposure to NO₂ based on residence address of each gravida. Logistic regression was performed to evaluate the associations of ambient NO₂ exposure with preterm birth during six exposure periods, including the entire pregnancy, the first trimester, the second trimester, the third trimester, the last month, and the last week before delivery. Sensitivity analysis with a matched case-control design was conducted to test the robustness of the association between NO₂ exposure and preterm birth.

RESULTS

The average NO₂ concentrations during the entire pregnancy was 48.23 µg/m³ among all participants. A 10 µg/m³ increase in NO₂ concentrations was associated with preterm birth, with an adjusted odds ratio of 1.03 (95% confidence interval [CI]: 0.96,1.10) for exposures during the entire pregnancy, 1.00 (95%CI: 0.95,1.06) in the first trimester, 1.01 (95%CI: 0.96,1.07) in the second trimester, 1.07 (95%CI: 1.02,1.13) in the third trimester, 1.10 (95%CI: 1.04,1.15) and 1.05 (95%CI: 1.00,1.09) in the month and week before delivery, respectively. The results of the matched case-control analysis were generally consistent with those of main analyses.

CONCLUSION

NO₂ may increase the risk of preterm birth, especially for exposures during the third trimester, the month and the week before delivery in Shanghai, China.

Ambient Air Pollution Exposure and Fecundability in Women Undergoing In Vitro Fertilization

BACKGROUND

Limited research suggests ambient air pollution impairs fecundity but groups most susceptible have not been identified. We studied whether long-term ambient air pollution exposure prior to an in vitro fertilization (IVF) cycle was associated with successful livebirth, and whether associations were modified by underlying infertility diagnosis.

METHODS

Data on women initiating their 1st autologous IVF cycle in 2012-13 were obtained from four U.S. clinics. Outcomes included pregnancy, pregnancy loss, and livebirth. Annual average exposure to fine particulate matter (PM2.5), PM10, and nitrogen dioxide (NO2) prior to IVF start were estimated at residential address using a validated national spatial model incorporating land-use regression and universal kriging. We also assessed residential distance to major roadway. We calculated risk ratios (RR) using modified Poisson regression and evaluated effect modification (EM) by infertility diagnosis on additive and multiplicative scales.

RESULTS

Among 7,463 eligible participants, 36% had a livebirth. There was a non-significant indication of an association between PM2.5 or NO2 and decreased livebirth and increased pregnancy loss. Near roadway residence was associated with decreased livebirth (RR: 0.96, 95% CI: 0.82, 0.99. There was evidence for EM between high exposure to air pollutants and a diagnosis of diminished ovarian reserve (DOR) or male infertility and decreased livebirth.

CONCLUSIONS

Despite suggestive but uncertain findings for the overall effect of air pollution on fecundity, we found a suggestive indication that there may be synergistic effects of air pollution and DOR or male infertility diagnosis on livebirth. This suggests two possible targets for future research and intervention.

The association between air pollution and preterm birth and low birth weight in Guangdong, China

BACKGROUND

A mountain of evidence has shown that people's physical and mental health can be affected by various air pollutions. Poor pregnancy outcomes are associated with exposure to air pollution. Therefore, this study aims to investigate the association between air pollutions (PM2.5, PM10, SO2, NO2, CO, and O3) and preterm birth/low birth weight in Guangdong province, China.

METHOD

All maternal data and birth data from January 1, 2014 to December 31, 2015 were selected from a National Free Pre-pregnancy Check-ups system, and the daily air quality data of Guangdong Province was collected from China National Environmental Monitoring Center. 1784 women with either preterm birth information (n = 687) or low birth weight information (n = 1097) were used as experimental group. Control group included 1766 women with healthy birth information. Logistic regression models were employed to evaluate the effects of air pollutants on the risk of preterm birth and low birth weight.

RESULTS

The pollution levels of PM2.5, PM10, SO2, NO2, CO, and O3 in Guangdong province were all lower than the national air pollution concentrations. The concentrations of PM2.5, PM10, SO2, NO2 and CO had obvious seasonal trends with the highest in winter and the lowest in summer. O3 concentrations in September (65.72 μg/m3) and October (84.18 μg/m3) were relatively higher. After controlling for the impact of confounding factors, the increases in the risk of preterm birth were associated with each 10 μg/m3 increase in PM2.5 (OR 1.043, 95% CI 1.01-1.09) and PM10 (OR 1.039, 95% CI 1.01~1.14) during the first trimester and in PM2.5 (OR 1.038, 95% CI 1.01~1.12), PM10 (OR 1.024, 95% CI 1.02~1.09), SO2 (OR 1.081, 95% CI 1.01~1.29), and O3 (OR 1.016, 95% CI 1.004~1.35) during the third trimester. The increase in the risk of low birth weight was associated with PM2.5, PM10, NO2, and O3 in the first month and the last month.

CONCLUSION

This study provides further evidence for the relationships between air pollutions and preterm birth/low birth weight. Pregnant women are recommended to reduce or avoid exposure to air pollutions during pregnancy, especially in the early and late stages of pregnancy.

Ambient air pollution, H19/DMR methylation in cord blood and newborn size: A pilot study in Zhengzhou City, China

Prenatal exposure to air pollutants is believed to be associated with adverse birth outcomes. However, the potential mechanisms, especially the epigenetic modified effects, still remain unclear. This study was designed to explore the association of air pollution, H19/DMR methylation levels, and birth weight and length. A total of 527 mother-infant pairs were recruited from Houzhai Center Hospital, Zhengzhou. Air pollution data during the study period was collected. The methylation at H19 promoter region and H19 DMR in maternal and cord bloods were determined using real-time PCR analysis. Ridge regression was used to analyze the association of air pollutants exposure during gestation with H19/DMR methylation and birth weight and length respectively. Results showed that prenatal exposure to NO₂ was associated with higher H19 methylation in cord blood. Whereas SO₂ and PM₁₀ exposure were associated with lower H19 and H19 DMR methylation respectively. After stratification by pregnancy trimesters, the association of H19 methylation in cord blood with PM₁₀ exposure also was found. Furthermore, prenatal exposures to air pollutants also were associated with birth weight and length. Specifically, with the increase of maternal SO₂ exposure during the entire pregnancy, birth weight and length significantly decreased. While birth weight and birth length were significantly increased with NO₂ exposure. The stratified analysis also found the associations between PM₁₀ exposure and birth sizes in different trimesters. In conclusion, the gene methylation level in cord blood might be associated with prenatal environmental exposures. Birth weight and length were associated with both prenatal environmental exposures and genetic factors.

Identifying windows of susceptibility for maternal exposure to ambient air pollution and preterm birth

Maternal exposure to ambient air pollution has been associated with preterm birth (PTB), however, entire pregnancy or trimester-specific associations were generally reported, which may not sufficiently identify windows of susceptibility. Using birth registry data from Guangzhou, a megacity of southern China (population ~14.5 million), including 469,975 singleton live births between January 2015 and July 2017, we assessed the association between weekly air pollution exposure and PTB in a retrospective cohort study. Daily average concentrations of PM_2.5, PM₁₀, NO₂, SO₂, and O₃ from 11 monitoring stations were used to estimate district-specific exposures for each participant based on their district residency during pregnancy. Distributed lag models (DLMs) incorporating Cox proportional hazard models were applied to estimate the association between weekly maternal exposure to air pollutant and PTB risk (as a time-to-event outcome), after controlling for temperature, seasonality, and individual-level covariates. We also considered moderate PTB (32-36 gestational weeks) and very PTB (28-31 gestational weeks) as outcomes of interest. Hazard ratios (HRs) and 95% confidential intervals (95% CIs) were calculated for an interquartile range (IQR) increase in air pollutants during the study period. An IQR increase in PM_2.5 exposure during the 20th to 28th gestational weeks (27.0 μg/m³) was significantly associated with PTB risk, with the strongest effect in the 25th week (HR = 1.034, 95% CI:1.010-1.059). The significant exposure windows were the 19th-28th weeks for PM₁₀, the 18th-31st weeks for NO₂, and the 23rd-31st weeks for O₃, respectively. The strongest associations were observed in the 25th week for PM₁₀ (IQR = 37.0 μg/m³; HR = 1.048, 95% CI:1.034-1.062), the 26th week for NO₂ (IQR = 29.0 μg/m³; HR = 1.060, 95% CI:1.028-1.094), and in the 28th week for O₃ (IQR = 90.0 μg/m³; HR = 1.063, 95% CI:1.046-1.081). Similar patterns were observed for moderate PTB (32-36 gestational weeks) and very PTB (28-31 gestational weeks) for PM_2.5, PM₁₀, NO₂ exposure, but the effects were greater for very PTB. We did not observe any association between pregnancy SO₂ exposure and the risk of PTB. Our results suggest that middle to late pregnancy is the most susceptible air pollution exposure window for air pollution and PTB among women in Guangzhou, China.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

Associations between maternal residential proximity to air emissions from industrial facilities and low birth weight in Texas, USA

BACKGROUND

Most previous studies examining associations between maternal exposures to air pollutants during pregnancy and low birth weight (LBW) in offspring focused on criteria air pollutants (PM_2.5, PM₁₀, O₃, NO₂, SO₂, CO, and Pb). The relationship between non-criteria air pollutants and LBW is understudied and requires greater coverage.

OBJECTIVES

This study investigated associations between maternal residential exposure to industrial air pollutants during pregnancy and LBW in offspring.

METHODS

This study used a case-control study design that included 94,106 term LBW cases and 376,424 controls. It covered 78 air pollutants common to both the Toxics Release Inventory (TRI) and ground air quality monitoring databases in Texas during 1996-2008. A modified version of the Emission Weighted Proximity Model (EWPM), calibrated with ground monitoring data, was used to estimate maternal residential exposure to industrial air pollutants during pregnancy. Binary logistic regression analyses were performed to calculate odds ratios (ORs) reflecting the associations of maternal exposure to industrial air pollutants and LBW in offspring, adjusted for child's sex, gestational weeks, maternal age, education, race/ethnicity, marital status, prenatal care, tobacco use during pregnancy, public health region of maternal residence, and year of birth. In addition, the Bonferroni correction for multiple comparisons was applied to the results of logistic regression analysis.

RESULTS

Relative to the non-exposed reference group, maternal residential exposure to benzene (adjusted odds ratio (aOR) 1.06, 95% confidence interval (CI) 1.04, 1.08), benzo(g,h,i)perylene (aOR 1.04, 95% CI 1.02, 1.07), cumene (aOR 1.05, 95% CI 1.03, 1.07), cyclohexane (aOR 1.04, 95% CI 1.02, 1.07), dichloromethane (aOR 1.04, 95% CI 1.03, 1.07), ethylbenzene (aOR 1.05, 95% CI 1.03, 1.06), ethylene (aOR 1.06, 95% CI 1.03, 1.09), mercury (aOR 1.04, 95% CI 1.02, 1.07), naphthalene (aOR 1.03, 95% CI 1.01, 1.05), n-hexane (aOR 1.06, 95% CI 1.04, 1.08), propylene (aOR 1.06, 95% CI 1.03, 1.10), styrene (aOR 1.06, 95% CI 1.04, 1.08), toluene (aOR 1.05, 95% CI 1.03, 1.07), and zinc (fume or dust) (aOR 1.10, 95% CI 1.06, 1.13) was found to have significantly higher odds of LBW in offspring. When the estimated exposures were categorized into four different groups (zero, low, medium, and high) in the analysis, eleven of the fourteen air pollutants, with the exception of benzo(g,h,i)perylene, ethylene, and propylene, remained as significant risk factors.

CONCLUSIONS

Results indicate that maternal residential proximity to industrial facilities emitting any of the fourteen pollutants identified by this study during pregnancy may be associated with LBW in offspring. With the exception of benzene, ethylbenzene, toluene, and zinc, the rest of the fourteen air pollutants are identified as LBW risk factors for the first time by this study. Further epidemiological, biological, and toxicological studies are suggested to verify the findings from this study.

Industrial air pollution and low birth weight: a case-control study in Texas, USA

Many studies have investigated associations between maternal residential exposures to air pollutants and low birth weight (LBW) in offspring. However, most studies focused on the criteria air pollutants (PM_2.5, PM₁₀, O₃, NO₂, SO₂, CO, and Pb), and only a few studies examined the potential impact of other air pollutants on LBW. This study investigated associations between maternal residential exposure to industrial air emissions of 449 toxics release inventory (TRI) chemicals and LBW in offspring using a case-control study design based on a large dataset consisting of 94,106 LBW cases and 376,424 controls in Texas from 1996 to 2008. Maternal residential exposure to chemicals was estimated using a modified version of the emission-weighted proximity model (EWPM). The model takes into account reported quantities of annual air emission from industrial facilities and the distances between the locations of industrial facilities and maternal residence locations. Binary logistic regression was used to compute odds ratios measuring the association between maternal exposure to different TRI chemicals and LBW in offspring. Odds ratios were adjusted for child's sex, birth year, gestational length, maternal age, education, race/ethnicity, and public health region of maternal residence. Among the ten chemicals selected for a complete analysis, maternal residential exposures to five TRI chemicals were positively associated with LBW in offspring. These five chemicals include acetamide (adjusted odds ratio [aOR] 2.29, 95% confidence interval [CI] 1.24, 4.20), p-phenylenediamine (aOR 1.63, 95% CI 1.18, 2.25), 2,2-dichloro-1,1,1-trifluoroethane (aOR 1.41, 95% CI 1.20, 1.66), tributyltin methacrylate (aOR 1.20, 95% CI 1.06, 1.36), and 1,1,1-trichloroethane (aOR 1.11, 95% CI 1.03, 1.20). These findings suggest that maternal residential proximity to industrial air emissions of some chemicals during pregnancy may be associated with LBW in offspring.

Environmental Contaminants and Congenital Heart Defects: A Re-Evaluation of the Evidence

Congenital heart defects (CHDs) are a common birth defect of largely unknown etiology, with high fetal and neonatal mortality. A review of CHDs and environmental contaminant exposure found that meta-analyses showed only modest associations for smoking, vehicle exhaust components, disinfectant by-products and proximity to incinerators, with stronger results from the newer, larger and better quality studies masked by the typical absence of effect in older studies. Recent studies of exposure to agricultural pesticides, solvents, metals and landfill sites also showed associations. Certain contaminants have been associated with certain CHDs, with septal defects being the most common. Frequent methodological problems include failure to account for potential confounders or maternal/paternal preconception exposure, differences in diagnosing, defining and classifying CHDs, grouping of defects to increase power, grouping of contaminants with dissimilar mechanisms, exclusion of pregnancies that result in death or later life diagnosis, and the assumption that maternal residence at birth is the same as at conception. Furthermore, most studies use measurement estimates of one exposure, ignoring the many additional contaminant exposures in daily life. All these problems can distort and underestimate the true associations. Impaired methylation is a common mechanism, suggesting that supplementary folate may be protective for any birth defect.

Association between ambient air pollutants and preterm birth in Ningbo, China: a time-series study

BACKGROUND

Exposure to air pollutants has been related to preterm birth, but little evidence can be available for PM2.5, O3 and CO in China. This study aimed to investigate the short-term effect of exposure to air pollutants on risk preterm birth during 2014-2016 in Ningbo, China.

METHODS

We conducted a time-series study to evaluate the associations between daily preterm birth and major air pollutants (including PM2.5, PM10, SO2, NO2, O3 and CO) in Ningbo during 2014-2016. A General Additive Model extend Poisson regression was used to evaluate the relationship between preterm birth and air pollution with adjustment for time-trend, meteorological factors and day of the week (DOW). We also conducted a subgroup analysis by season and age.

RESULTS

In this study, a total of 37,389 birth occurred between 2014 and 2016 from the Electronic Medical Records System of Ningbo Women and Children's Hospital, of which 5428 were verified as preterm birth. The single pollutant model suggested that lag effect of PM2.5, PM10, NO2 reached a peak at day 3 before delivery and day 6 for SO2, and no relationships were observed for O3 and preterm birth. Excess risks (95% confidence intervals) for an increase of IQR of air pollutant concentrations were 4.84 (95% CI: 1.77, 8.00) for PM2.5, 3.56 (95% CI: 0.07, 7.17) for PM10, 3.65 (95% CI: 0.86, 6.51) for SO2, 6.49 (95% CI: 1.86, 11.34) for NO2, - 0.90 (95% CI: -4.76, 3.11) for O3, and 3.36 (95% CI: 0.50, 6.30) for CO. Sensitivity analyses by exclusion of maternal age < 18 or > 35 years did not materially alter our results.

CONCLUSIONS

This study indicates that short-term exposure to air pollutants (including PM2.5, PM10, SO2, NO2) are positively associated with risk of preterm birth in Ningbo, China.

The association between ambient PM2.5 exposure and the risk of preterm birth in China: A retrospective cohort study

BACKGROUND

The relationship between PM2.5 exposure and preterm birth remains unclear.

OBJECTIVES

To explore the effect of exposure to PM2.5 on preterm birth in China.

METHODS

The birth outcomes of 426,246 pregnant women enrolled between January 2014 and December 2014 in NFPCP (National Free Pre-pregnancy Checkups Project) were collected, and their individual PM2.5 exposure values were estimated from the China National Environmental Monitoring Centre. The time of gestational exposure to PM2.5 was divided into four periods (the first trimester, the second trimester, the third trimester and the entire pregnancy). The average concentration and the corresponding quartiles of PM2.5 were calculated in these periods by the daily average PM2.5 data. Cox proportional hazards regression was used and he effects of maternal age, education level, occupation, second-hand smoking, alcohol use, pre-pregnancy BMI, baby's sex, number of previous pregnancies, coastal areas and season of conception were adjusted for.

RESULTS

A total of 426,246 singleton births were included, among which 35,261 (8.3%) were preterm birth. Effect of each 10μg/m³ increase of PM2.5 on preterm birth was most significant during the third trimester (HR, 1.06; 95%CI, 1.06-1.07), and also significant during the first trimester (HR, 1.04; 95%CI, 1.03-1.04), the second trimester (HR, 1.02; 95%CI, 1.02-1.02) and the entire pregnancy (HR, 1.06; 95%CI, 1.05-1.06). Compared with the lowest quartile of PM2.5, other quartiles increased the risk of preterm birth, and were most significant during the third trimester (HR, 1.87; 95%CI, 1.69-2.06). Subgroup analysis showed that compared with other subgroups, women who were older than 30years, had low education level, worked as farmers, had male baby, had previous pregnancies, not live in coastal areas and pregnant in winter were more sensitive to PM2.5 exposure.

CONCLUSIONS

Ambient PM2.5 exposure during pregnancy played an important role in the pregnancy process and increased the risk of preterm birth.

Mortality and morbidity in populations in the vicinity of coal mining: a systematic review

BACKGROUND

Evidence of the association of coal mining with health outcomes such as increased mortality and morbidity in the general population has been provided by epidemiological studies in the last 25 years. Given the diverse sources of data included to investigate different health outcomes in the exposed populations, the International Classification of Diseases (ICD) can be used as a single classification standard to compare the findings of studies conducted in different socioeconomic and geographic contexts. The ICD classifies diagnoses of diseases and other disorders as codes organized by categories and chapters.

OBJECTIVES

Identify the ICD codes found in studies of morbidity and/or mortality in populations resident or in proximity of coal mining and assess the methods of these studies conducting a systematic review.

METHODS

A systematic database search of PubMed, EMBASE and Scopus following the PRISMA protocol was conducted to assess epidemiological studies from 1990 to 2016. The health outcomes were mapped to ICD codes and classified by studies of morbidity and/or mortality, and the categories and chapters of the ICD.

RESULTS

Twenty-eight epidemiological studies with ecological design from the USA, Europe and China were included. The exposed populations had increased risk of mortality and/or morbidity by 78 ICD diagnosis categories and 9 groups of ICD categories in 10 chapters of the ICD: Neoplasms, diseases of the circulatory, respiratory and genitourinary systems, metabolic diseases, diseases of the eye and the skin, perinatal conditions, congenital and chromosomal abnormalities, and external causes of morbidity. Exposed populations had non-increased risk of 9 ICD diagnosis categories of diseases of the genitourinary system, and prostate cancer.

CONCLUSIONS

There is consistent evidence of the association of coal mining with a wide spectrum of diseases in populations resident or in proximity of the mining activities. The methods of the studies included in this review can be integrated with individual-level and longitudinal studies to provide further evidence of the exposure pathways linked to increased risk in the exposed populations.

Outdoor air pollution and respiratory health: a bibliometric analysis of publications in peer-reviewed journals (1900 - 2017)

BACKGROUND

Outdoor air pollution is a major threat to global public health that needs responsible participation of researchers at all levels. Assessing research output is an important step in highlighting national and international contribution and collaboration in a certain field. Therefore, the aim of this study was to analyze globally-published literature in outdoor air pollution - related respiratory health.

METHOD

Outdoor air pollution documents related to respiratory health were retrieved from Scopus database. The study period was up to 2017. Mapping of author keywords was carried out using VOSviewer 1.6.6.

RESULTS

Search query yielded 3635 documents with an h-index of 137. There was a dramatic increase in the number of publications in the last decade of the study period. The most frequently encountered author keywords were: air pollution (835 occurrences), asthma (502 occurrences), particulate matter (198 occurrences), and children (203 occurrences). The United States of America ranked first (1082; 29.8%) followed by the United Kingdom (279; 7.7%) and Italy (198; 5.4%). Annual research productivity stratified by income and population size indicated that China ranked first (22.2) followed by the USA (18.8). Analysis of regional distribution of publications indicated that the Mediterranean, African, and South-East Asia regions had the least contribution. Harvard University (92; 2.5%) was the most active institution/organization followed the US Environmental Protection Agency (89; 2.4%). International collaboration was restricted to three regions: Northern America, Europe, and Asia. The top ten preferred journals were in the field of environmental health and respiratory health. Environmental Health Perspective was the most preferred journal for publishing documents in outdoor pollution in relation to respiratory health.

CONCLUSION

Research on the impact of outdoor air pollution on respiratory health had accelerated lately and is receiving a lot of interest. Global research networks that include countries with high level of pollution and limited resources are highly needed to create public opinion in favor of minimizing outdoor air pollution and investing in green technologies.

Household environmental exposures during gestation and birth outcomes: A cross-sectional study in Shanghai, China

Several studies have reported that certain aspects of the household environments are associated with adverse birth outcomes, but associations have been inconsistent. Few of these studies have been conducted in China. During 2011-2012, we conducted a retrospective cross-sectional study and collected 13,335 parents-reported questionnaires for 4-6-year-olds children in Shanghai, China. We investigated associations of household environmental factors (environmental tobacco smoke (ETS), cooking fuel, dampness, pet-keeping, and home renovation) during gestation with preterm birth (PTB, gestational age<37weeks), low birth weight (LBW, birth weight<2500g), term low birth weight (T-LBW, LBW when the gestational age was ≥37weeks), and small for gestational age (SGA, birth weight<10th percentile of birth weight for gestational age). A total of 4.1% children were premature; 2.9% had LBW and 1.6% had T-LBW; 8.1% were SGA. In the multiple logistic regression analyses, home renovation during gestation was associated with PTB (adjusted odds ratio (OR), 95% confidence intervals (CI): 1.68, 1.11-2.54) and LBW (1.64, 0.99-2.72). Paternal smoking was associated with PTB (1.18, 0.98-1.43). No significant associations were found for SGA. Neither household dampness nor cooking fuel were significantly associated with birth outcomes. For boys, paternal smoking was associated with PTB (1.31, 1.02-1.69); home renovation during gestation was associated with PTB (2.14, 1.27-3.61) and LBW (2.19, 1.09-4.43). Among children whose mothers were ≥34-year-olds during gestation, paternal smoking (1.73, 1.04-2.76) and home renovation during gestation (1.80, 1.18-2.76) was associated with PTB. Our findings demonstrate that home renovation and ETS during gestation may be risk factors for adverse birth outcomes. Associations of these factors with adverse birth outcomes appear to be stronger in boys and among mothers older than 34years during gestation. Home renovation and ETS exposure should be avoided during gestation, especially for pregnancies with male fetuses and older pregnant women.

Ambient air pollution and the risk of pregnancy loss: a prospective cohort study

OBJECTIVE

To estimate the association of pregnancy loss with common air pollutant exposure. Ambient air pollution exposure has been linked to adverse pregnancy outcomes, but few studies have investigated its relationship with pregnancy loss.

DESIGN

Prospective cohort study.

SETTING

Not applicable.

PATIENT(S)

A total of 343 singleton pregnancies in a multisite prospective cohort study with detailed protocols for ovulation and pregnancy testing.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Timing of incident pregnancy loss (from ovulation).

RESULT(S)

The incidence of pregnancy loss was 28% (n = 98). Pollutant levels at women's residences were estimated using modified Community Multiscale Air Quality models and averaged during the past 2 weeks (acute) and the whole pregnancy (chronic). Adjusted Cox proportional hazards models showed that an interquartile range increase in average whole pregnancy ozone (hazard ratio [HR] 1.12, 95% confidence interval [CI] 1.07-1.17) and particulate matter <2.5 μm (HR 1.13, 95% CI 1.03-1.24) concentrations were associated with faster time to pregnancy loss. Sulfate compounds also appeared to increase risk (HR 1.58, 95% CI 1.07-2.34). Last 2 weeks of exposures were not associated with loss.

CONCLUSION(S)

In a prospective cohort of couples trying to conceive, we found evidence that exposure to air pollution throughout pregnancy was associated with loss, but delineating specific periods of heightened vulnerability await larger preconception cohort studies with daily measured air quality.

Exposure to particulate air pollution during early pregnancy is associated with placental DNA methylation

Maternal exposure to particulate matter with aerodynamic diameter <10μm (PM₁₀) during pregnancy results in adverse birth outcomes. Changes in placental DNA methylation might mediate those adverse effects. In this study, we examined the associations between prenatal PM₁₀ exposure and DNA methylation of LINE1, HSD11B2 and NR3C1 in human placenta. One hundred and eighty-one mother newborn pairs (80 fetal growth restriction newborns, 101 normal newborns) participated in this study. The average PM₁₀ exposure of each trimester and of the whole pregnancy was calculated using daily air pollution concentration data. Placental DNA methylation was measured by quantitative polymerase chain reaction-pyrosequencing. Placental LINE-1 DNA methylation was reversely associated with first trimester PM₁₀ exposure 1.78% (-β=1.78, 95% CI: -3.35, -0.22%), while placental HSD11B2 DNA methylation was associated with both first and second trimester PM₁₀ exposure, and relatively increased by 1.03% (95% CI: 0.07, 1.98%) and 2.33% (95% CI: 0.69, 3.76%) for each 10μg/m³ increase in exposure to PM₁₀. Those associations were much more evident in fetal growth restriction newborns than those in normal newborns. In summary, early pregnancy PM₁₀ exposure was associated with placental DNA methylation of LINE1 and HSD11B2, suggesting that such methylation alterations might mediate PM-induced reproductive and developmental toxicity.

Association between exposure to particulate matter during pregnancy and birthweight: a systematic review and a meta-analysis of birth cohort studies

Studies of the associations between maternal exposure to particulate matter (PM) and risk of adverse effects on fetal growth are inconsistent and inconclusive. This question can be well answered by carefully designed birth cohort studies; however, so far the evidence from such studies has not come to the same conclusion. We sought to evaluate the association between maternal exposures to PM and low birthweight (LBW) enrolling 14 studies from 11 centers, and to explore the influence of trimester and exposure assessment methods on between-center heterogeneity in this association. Data were derived from PubMed, Embase, Google Scholar, CNKI, and WanFang database, references from relevant articles, and results from published studies until March 2017. Using a random-effects meta-analysis, we combined the coefficient and odds ratios (OR) of individual studies conducted among 14 birth cohort studies. Random-effect meta-analysis results suggested that a 17% and 6% increase in risk of LBW was relevant to a 10 mg/m3 rise in PM2.5 and PM10 exposure concentrations at the 3rd trimester (pooled odds ratios (OR), 1.17 and 1.06; 95% confidence interval (CI), 0.94-1.46 and 0.97-1.15, respectively), but the null value was included in our 95% CI. Our results showed that exposure to PM2.5 and PM10 during pregnancy has a positive relevance to LBW based on birth cohort studies. However, neither reached formal statistical significance. Negative impacts on outcomes of birth is implied by maternal exposure to PM. Further mechanistic researches are needed to explain the connection between PM pollution and LBW.

Maternal exposure to air pollutants during the first trimester and foetal growth in Japanese term infants

Evidence supporting an inverse association between maternal exposure to air pollutants and foetal growth has been accumulating. However, the findings from Asian populations are limited, and the question of critical windows of exposure remains unanswered. We examined whether maternal exposure to air pollutants, in particular exposure during the first trimester (an important period of placental development), was associated with foetal growth in Japanese term infants. From the Japan Perinatal Registry Network database, we received birth data for 29,177 term singleton births in western Japan (Kyushu-Okinawa Districts) between 2005 and 2010. Exposure was expressed in terms of average concentrations of air pollutants (ozone, suspended particulate matter, nitrogen dioxide, and sulphur dioxide), as measured at the nearest monitoring stations to the respective delivery hospitals of the pregnant women, during the entire pregnancy and each trimester. As proxy markers of foetal growth restriction, we used small for gestational age (SGA), and adverse birth weight (low birth weight in addition to SGA). For pollutant exposure during the entire pregnancy, we did not observe the association with SGA and adverse birth weight. In the single-trimester model for the first trimester, however, we found a positive association between ozone exposure, and SGA (odds ratio [OR] per 10 ppb increase = 1.07, 95% confidence interval [CI] = 1.01-1.12) and adverse birth weight (OR = 1.07; 95% CI = 1.01-1.14). This association persisted in the multi-trimester model, and no association for exposure during the second or third trimester was observed. Exposure to other pollutants during each trimester was not associated with these outcomes. In conclusion, maternal exposure to ozone during the first trimester was independently associated with an elevated risk of poor foetal growth.

Transport and public health in China: the road to a healthy future

Transportation-related risk factors are a major source of morbidity and mortality in China, where the expansion of road networks and surges in personal vehicle ownership are having profound effects on public health. Road traffic injuries and fatalities have increased alongside increased use of motorised transport in China, and accident injury risk is aggravated by inadequate emergency response systems and trauma care. National air quality standards and emission control technologies are having a positive effect on air quality, but persistent air pollution is increasingly attributable to a growing and outdated vehicle fleet and to famously congested roads. Urban design favours motorised transport, and physical activity and its associated health benefits are hindered by poor urban infrastructure. Transport emissions of greenhouse gases contribute substantially to regional and global climate change, which compound public health risks from multiple factors. Despite these complex challenges, technological advances and innovations in planning and policy stand to make China a leader in sustainable, healthy transportation.

Ambient temperature and air quality in relation to small for gestational age and term low birthweight

BACKGROUND

Exposures to extreme ambient temperature and air pollution are linked to adverse birth outcomes, but the associations with small for gestational age (SGA) and term low birthweight (tLBW) are unclear. We aimed to investigate exposures to site-specific temperature extremes and selected criteria air pollutants in relation to SGA and tLBW.

METHODS

We linked medical records of 220,572 singleton births (2002-2008) from 12 US sites to local temperature estimated by the Weather Research and Forecasting model, and air pollution estimated by modified Community Multiscale Air Quality models. Exposures to hot (>95th percentile) and cold (<5th percentile) were defined using site-specific distributions of daily temperature over three-month preconception, each trimester, and whole-pregnancy. Average concentrations of five criteria air pollutants and six fine particulate matter constituents were also calculated for these pregnancy windows. Poisson regression with generalized estimating equations calculated the relative risks (RR) and 95% confidence intervals for SGA (weight <10th percentile conditional on gestational age and sex) and tLBW (≥37 weeks and <2500g) associated with an interquartile range increment of air pollutants, and cold or hot compared to mild (5-95th percentile) temperature. Models were adjusted for maternal demographics, lifestyle, and clinical factors, season, and site.

RESULTS

Compared to mild temperature, cold exposure during trimester 2 [RR: 1.21 (1.05-1.38)], trimester 3 [RR: 1.18 (1.03-1.36)], and whole-pregnancy [RR: 2.57 (2.27-2.91)]; and hot exposure during trimester 3 [RR: 1.31 (1.15-1.50)] and whole-pregnancy [RR: 2.49 (2.20-2.83)] increased tLBW risk. No consistent association was observed between temperature and SGA. Air pollutant analyses were generally null but preconception elemental carbon was associated with a 4% increase in SGA while dust particles increased tLBW by 10%. Particulate matter ≤10µm in the second trimester and whole pregnancy also appeared related to tLBW.

CONCLUSIONS

Our findings suggest prenatal exposures to extreme ambient temperature relative to usual environment may increase tLBW risk. Given concerns related to climate change, these findings merit further investigation.

The Associations Between Air Pollution and Adverse Pregnancy Outcomes in China

Research on the potential impact of air pollution on the human's health has increased rapidly in recent years. Several studies have suggested that exposure to air pollutants during period of pregnancy which is a crucial time point of mother-fetus development may have long-term and serious impact on adverse pregnancy outcomes. There is lack of review to evaluate the existed epidemiologic evidence on the associations between air pollutants and adverse pregnancy outcomes in China, so we conducted a review to explore the current epidemiological evidence on the effects of air pollutants to pregnancy outcomes and possible mechanisms during the pregnancy process. We used keywords to systematically search all the English and Chinese literatures on studies that were conducted in China. Exposure to air pollutants during pregnancy had shown there were harmful effects for different birth outcomes: preterm birth, low birth weight, stillbirth, birth defects, infertility, and macrosomia fetus. Results on the effects of air pollutants on adverse pregnancy outcomes are small and inconsistent because they vary in their design and methodology. The existed available evidence is compatible with either a small negative effect of air pollutants on pregnancy outcomes or with no effect; therefore, further studies are needed to confirm and quantify the possible associations and potential biologic mechanisms between air pollutants and pregnancy outcomes.