Acute effects of air pollutants on spontaneous pregnancy loss: a case-crossover study

The causal effect of exposure to air pollution on risk of adverse pregnancy outcomes: A two-sample Mendelian randomisation study

BACKGROUND

Epidemiological studies have examined the relation between air pollution (NOx, NO2, PM2.5, PM2.5-10, and PM10) and adverse pregnancy outcomes (APOs). There's increasing evidence that air pollution increases the risk of APOs. However, the results of these studies are controversial, and the causal relation remains uncertain. We aimed to assess whether a genetic causal link exists between air pollution and APOs and the potential effects of this relation.

METHODS

A novel two-sample Mendelian randomisation (MR) study used pooled data from a large-scale complete genome correlation study. The primary analysis method was inverse variance weighting (IVW), which explored the expose-outcome relationship for assessing single nucleotide polymorphisms (SNPs) associated with air pollution. Further sensitivity analysis, including MR-PRESSO, MR-Egger regression, and leave-one analysis, was used to test the consistency of the results.

RESULTS

There was a significant correlation between air pollution-related SNPs and APOs. A robust causal link was found between genetic susceptibility to air pollution and APOs.

CONCLUSIONS

Our MR analysis reveals a genetic causal relation between air pollution and APOs, which may help provide new insights into further mechanisms and clinical studies in air pollution-mediated APOs.

Unhealthy air quality secondary to wildfires is associated with lower blastocyst yield

OBJECTIVE

To study the impact of unhealthy air quality from the 2020 Oregon wildfires on outcomes for patients undergoing in vitro fertilization (IVF) treatment.

DESIGN

A retrospective cohort study.

SETTING

A university-based fertility clinic.

PATIENTS

Subjects were undergoing IVF treatment from the 6 weeks preceding the wildfires through a 10-day exposure period. Cohorts were classified on the basis of whether subjects experienced patient and/or laboratory exposure to unhealthy air quality. Patient exposure was defined as at least 4 days of ovarian stimulation overlapping with the exposure, and laboratory exposure was defined as at least 2 days of IVF treatment and embryogenesis overlapping with the exposure. The unexposed cohort consisted of remaining subjects without defined exposure, with cycles in the 6 weeks preceding the wildfires. As some subjects had dual exposure and appeared in both patient and laboratory exposure cohorts, each cohort was separately compared with the unexposed control cohort.

INTERVENTION

A 10-day period of unhealthy air quality caused by smoke plumes from a wildfire event.

MAIN OUTCOME MEASURES

The primary outcome was the blastulation rate. Secondary outcomes included fertilization rate, number of blastocysts obtained, and cycles with no blastocysts frozen or transferred.

RESULTS

Sixty-nine subjects underwent ovarian stimulation and IVF treatment during the 6 weeks preceding the wildfires through the 10-day period of unhealthy air quality. Of these, 15 patients were in the laboratory exposure cohort, 16 were in the patient exposure cohort, and 44 were unexposed. Six subjects appeared in both laboratory and patient exposure cohorts. Although neither exposure cohort had significantly decreased blastulation rate compared with the unexposed, the median number of blastocysts obtained was significantly lower in the laboratory exposure cohort than the unexposed group (2 [range 0-14] vs. 4.5 [range 0-21], respectively). The laboratory exposure cohort had significantly more cycles with no blastocysts obtained (3/15 [20%] vs. 1/44 [2%]). There were no significant differences in IVF treatment outcomes between patient exposure and unexposed cohorts. These findings persisted after controlling for age. There were no significant differences in pregnancy outcomes observed after embryo transfer between the exposure group and the unexposed group.

CONCLUSION

For a cohort of patients undergoing IVF treatment, an acute episode of outside wildfire smoke exposure during fertilization and embryogenesis was associated with decreased blastocyst yield.

Ambient air pollution and rate of spontaneous abortion

Spontaneous abortion (SAB), defined as a pregnancy loss before 20 weeks of gestation, affects up to 30% of conceptions, yet few modifiable risk factors have been identified. We estimated the effect of ambient air pollution exposure on SAB incidence in Pregnancy Study Online (PRESTO), a preconception cohort study of North American couples who were trying to conceive. Participants completed questionnaires at baseline, every 8 weeks during preconception follow-up, and in early and late pregnancy. We analyzed data on 4643 United States (U.S.) participants and 851 Canadian participants who enrolled during 2013-2019 and conceived during 12 months of follow-up. We used country-specific national spatiotemporal models to estimate concentrations of particulate matter <2.5 μm (PM2.5), nitrogen dioxide (NO2), and ozone (O3) during the preconception and prenatal periods at each participant's residential address. On follow-up and pregnancy questionnaires, participants reported information on pregnancy status, including SAB incidence and timing. We fit Cox proportional hazards regression models with gestational weeks as the time scale to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of time-varying prenatal concentrations of PM2.5, NO2, and O3 with rate of SAB, adjusting for individual- and neighborhood-level factors. Nineteen percent of pregnancies ended in SAB. Greater PM2.5 concentrations were associated with a higher incidence of SAB in Canada, but not in the U.S. (HRs for a 5 μg/m3 increase = 1.29, 95% CI: 0.99, 1.68 and 0.94, 95% CI: 0.83, 1.08, respectively). NO2 and O3 concentrations were not appreciably associated with SAB incidence. Results did not vary substantially by gestational weeks or season at risk. In summary, we found little evidence for an effect of residential ambient PM2.5, NO2, and O3 concentrations on SAB incidence in the U.S., but a moderate positive association of PM2.5 with SAB incidence in Canada.

Obstetric care for environmental migrants

BACKGROUND

Migration due to environmental factors is an international crisis affecting many nations globally. Pregnant people are a vulnerable subgroup of migrants.

AIM

This article explores the potential effects of environmental migration on pregnancy and aims to draw attention to this rising concern.

METHODS

Based on the study aim, a semi-structured literature review was performed. The following databases were searched: MEDLine (PubMed) and Google Scholar. The search was originally conducted on 31st January 2021 and repeated on 22nd September 2022.

RESULTS

Pregnant migrants are at increased risk of mental health disorders, congenital anomalies, preterm birth, and maternal mortality. Pregnancies exposed to natural disasters are at risk of low birth weight, preterm birth, hypertensive disorders, gestational diabetes, and mental health morbidity. Along with the health risks, there are additional complex social factors affecting healthcare engagement in this population.

CONCLUSION

Maternity healthcare providers are likely to provide care for environmental migrants over the coming years. Environmental disasters and migration as individual factors have complex effects on perinatal health, and environmental migrants may be at risk of specific perinatal complications. Obstetricians and maternity healthcare workers should be aware of these challenges and appreciate the individualised and specialised care that these patients require.

A comprehensive review on endocrine toxicity of gaseous components and particulate matter in smog

Smog is a form of extreme air pollution which comprises of gases such as ozone, sulfur dioxide, nitrogen and carbon oxides, and solid particles including particulate matter (PM2.5 and PM10). Different types of smog include acidic, photochemical, and Polish. Smog and its constituents are hazardaous to human, animals, and plants. Smog leads to plethora of morbidities such as cancer, endocrine disruption, and respiratory and cardiovascular disorders. Smog components alter the activity of various hormones including thyroid, pituitary, gonads and adrenal hormones by altering regulatory genes, oxidation status and the hypothalamus-pituitary axis. Furthermore, these toxicants are responsible for the development of metabolic disorders, teratogenicity, insulin resistance, infertility, and carcinogenicity of endocrine glands. Avoiding fossil fuel, using renewable sources of energy, and limiting gaseous discharge from industries can be helpful to avoid endocrine disruption and other toxicities of smog. This review focuses on the toxic implications of smog and its constituents on endocrine system, their toxicodynamics and preventive measures to avoid hazardous health effects.

Relationship between air pollutants and spontaneous abortion in a coal resource valley city: a retrospective cohort study

OBJECTIVE

Pollutants in the atmosphere have been linked to poor pregnancy outcomes in women. However, such investigations are scarce in metropolitan northern China. The major exposure window of air pollution affecting pregnant women is also unknown.

METHODS

For the analysis, this retrospective cohort study enrolled 6960 pregnant women recorded at Tongchuan People's Hospital from January 2018 to December 2019. Pollutant concentration values from the nearest monitoring station to the pregnant women were used to estimate exposure doses for each exposure window. Logistic regression models were created to investigate the connection between pollutants and spontaneous abortion while controlling for confounding factors.

RESULTS

PM2.5 was a risk factor for spontaneous abortion in T3 (30-60 days before the first day of the last menstrual period [LMP]), (OR: 1.305, 95% CI: 1.143-1.490) and T4 (60-90 days before the first day of the LMP),(OR: 1.450, 95% CI: 1.239-1.696) after controlling for covariates. In the same window, PM10 was a risk factor (OR: 1.308, 95% CI: 1.140-1.500), (OR: 1.386, 95% CI: 1.184-1.621). In T2 (30 days before the first day of the LMP), T3, and T4, SO2 was a risk factor for spontaneous abortion (OR: 1.185, 95% CI: 1.025-1.371), (OR: 1.219, 95% CI: 1.071-1.396), (OR: 1.202, 95% CI: 1.040-1.389). In T3 and T4, NO2 was a risk factor (OR: 1.171, 95% CI: 1.019- 1.346), (OR: 1.443, 95% CI: 1.259-1.655). In T1 (from the first day of the LMP to the date of abortion), O3 was found to be a risk factor (OR: 1.366, 95% CI: 1.226-1.521).

CONCLUSION

Exposure to high levels of air pollutants before and during pregnancy may be a risk factor for spontaneous abortion in pregnant women. This study further illustrates the importance of reducing air pollution emissions.

Characterisation of personalised air pollution exposure in pregnant women participating in a birth cohort study

BACKGROUND

Air pollution is a health risk in pregnant women and children. Despite the importance of refined exposure assessment, the characterisation of personalised air pollution exposure remains a challenge in paediatric and perinatal epidemiology.

OBJECTIVE

We used portable personal air monitors to characterise personalised exposure to air pollutants in pregnant women.

METHODS

Between November 2019 and May 2022, we offered personal air monitors to pregnant women participating in a birth cohort in New York City. During pregnancy, women used air monitors, which measured particulate matter (PM), nitrogen dioxide (NO2 ), and volatile organic compounds (average use = 14 days). Data were stored in real-time on a secure database via synchronisation with a smartphone application. Of 497 women who agreed to use air monitors, 273 women (55%) were successful in using air monitors for longer than a day. For these participants, we identified daily patterns of exposure to air pollutants using functional principal component analysis (3827 days of air monitoring).

RESULTS

Compared to women with no pollution data (n = 224), women who successfully used monitors were more likely to be non-Hispanic White and Asian (vs. Hispanic), nulliparous, unemployed, married/partnered, and received the device in-person (vs. mailed). We identified different daily patterns of exposure to air pollutants. The most dominant pattern for all pollutants was low exposure levels with little variations within 24 h, followed by a pattern that showed differences between day and night levels. NO2 had higher daily variations compared to PM.

CONCLUSIONS

Small wearables are useful for the measurement of personalised air pollution exposure in birth cohorts and identify daily patterns that cannot be captured otherwise. Successful participation, however, depends on certain individual characteristics. Future studies should consider strategies in design and analysis to account for selective participation.

Aerosol Measurement Degradation in Low-Cost Particle Sensors Using Laboratory Calibration and Field Validation

Increasing concern over air pollution has led to the development of low-cost sensors suitable for wide-scale deployment and use by citizen scientists. This project investigated the AirU low-cost particle sensor using two methods: (1) a comparison of pre- and post-deployment calibration equations for 24 devices following use in a field study, and (2) an in-home comparison between 3 AirUs and a reference instrument, the GRIMM 1.109. While differences (and therefore some sensor degradation) were found in the pre- and post-calibration equation comparison, absolute value changes were small and unlikely to affect the quality of results. Comparison tests found that while the AirU did tend to underestimate minimum and overestimate maximum concentrations of particulate matter, ~88% of results fell within ±1 μg/m³ of the GRIMM. While these tests confirm that low-cost sensors such as the AirU do experience some sensor degradation over multiple months of use, they remain a valuable tool for exposure assessment studies. Further work is needed to examine AirU performance in different environments for a comprehensive survey of capability, as well as to determine the source of sensor degradation.

Associations between maternal exposure to ambient air pollution and very low birth weight: A birth cohort study in Chongqing, China

Introduction

There have been many researches done on the association between maternal exposure to ambient air pollution and adverse pregnancy outcomes, but few studies related to very low birth weight (VLBW). This study thus explores the association between maternal exposure to ambient air pollutants and the risk of VLBW, and estimates the sensitive exposure time window.

Methods

A retrospective cohort study analyzed in Chongqing, China, during 2015-2020. The Generalized Additive Model were applied to estimate exposures for each participant during each trimester and the entire pregnancy period.

Results

For each 10 μg/m³ increase in PM_2.5 during pregnancy, the relative risk of VLBW increased on the first trimester, with RR = 1.100 (95% CI: 1.012, 1.195) in the single-pollutant model. Similarly, for each 10 μg/m³ increase in PM₁₀, there was a 12.9% (RR = 1.129, 95% CI: 1.055, 1.209) increase for VLBW on the first trimester in the single-pollutant model, and an 11.5% (RR = 1.115, 95% CI: 1.024, 1.213) increase in the multi-pollutant model, respectively. The first and second trimester exposures of NO₂ were found to have statistically significant RR values for VLBW. The RR values on the first trimester were 1.131 (95% CI: 1.037, 1.233) and 1.112 (95% CI: 1.015, 1.218) in the single-pollutant model and multi-pollutant model, respectively; The RR values on the second trimester were 1.129 (95% CI: 1.027, 1.241) and 1.146 (95% CI: 1.038, 1.265) in the single-pollutant model and multi-pollutant model, respectively. The RR of O3 exposure for VLBW on the entire trimester was 1.076 (95% CI: 1.010-1.146), and on the second trimester was 1.078 (95% CI: 1:016, 1.144) in the single-pollutant model.

Conclusion

This study indicates that maternal exposure to high levels of PM_2.5, PM₁₀, NO₂, and O₃ during pregnancy may increase the risk of very low birth weight, especially for exposure on the first and second trimester. Reducing the risk of early maternal exposure to ambient air pollution is thus necessary for pregnant women.

Construction of machine learning tools to predict threatened miscarriage in the first trimester based on AEA, progesterone and β-hCG in China: a multicentre, observational, case-control study

Background

Endocannabinoid anandamide (AEA), progesterone (P4) and β-human chorionic gonadotrophin (β-hCG) are associated with the threatened miscarriage in the early stage. However, no study has investigated whether combing these three hormones could predict threatened miscarriage. Thus, we aim to establish machine learning models utilizing these three hormones to predict threatened miscarriage risk.

Methods

This is a multicentre, observational, case-control study involving 215 pregnant women. We recruited 119 normal pregnant women and 96 threatened miscarriage pregnant women including 58 women with ongoing pregnancy and 38 women with inevitable miscarriage. P4 and β-hCG levels were detected by chemiluminescence immunoassay assay. The level of AEA was tested by ultra-high-performance liquid chromatography-tandem mass spectrometry. Six predictive machine learning models were established and evaluated by the confusion matrix, area under the receiver operating characteristic (ROC) curve (AUC), accuracy and precision.

Results

The median concentration of AEA was significantly lower in the healthy pregnant women group than that in the threatened miscarriage group, while the median concentration of P4 was significantly higher in the normal pregnancy group than that in the threatened miscarriage group. Only the median level of P4 was significantly lower in the inevitable miscarriage group than that in the ongoing pregnancy group. Moreover, AEA is strongly positively correlated with threatened miscarriage, while P4 is negatively correlated with both threatened miscarriage and inevitable miscarriage. Interestingly, AEA and P4 are negatively correlated with each other. Among six models, logistic regression (LR), support vector machine (SVM) and multilayer perceptron (MLP) models obtained the AUC values of 0.75, 0.70 and 0.70, respectively; and their accuracy and precision were all above 0.60. Among these three models, the LR model showed the highest accuracy (0.65) and precision (0.70) to predict threatened miscarriage.

Conclusions

The LR model showed the highest overall predictive power, thus machine learning combined with the level of AEA, P4 and β-hCG might be a new approach to predict the threatened miscarriage risk in the near feature.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-05025-y.

The acute effect and lag effect analysis between exposures to ambient air pollutants and spontaneous abortion: a case-crossover study in China, 2017-2019

INTRODUCTION

Recent studies demonstrated that living in areas with high ambient air pollution may have adverse effects on pregnancy outcomes, but few studies have investigated its association with spontaneous abortion. Further investigation is needed to explore the acute effect and lag effect of air pollutants exposure on spontaneous abortion.

OBJECTIVE

To investigate the acute effect and lag effect between exposure to ambient air pollutants and spontaneous abortion.

METHODS

Research data of spontaneous abortion were collected from the Chongqing Health Center for Women and Children (CQHCWC) in China. The daily ambient air pollution exposure measurements were estimated for each woman using inverse distance weighting from monitoring stations. A time-stratified, case-crossover design combined with distributed lag linear models was applied to assess the associations between spontaneous pregnancy loss and exposure to each of the air pollutants over lags 0-7 days, adjusted for temperature and relative humidity.

RESULTS

A total of 1399 women who experienced spontaneous pregnancy loss events from November 1, 2016, to September 30, 2019, were selected for this study. Maternal exposure to particulate matter 2.5 (PM_2.5), particle matter 10 (PM₁₀) nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) exhibited a significant association with spontaneous abortion. For every 20 μg/m³ increase in PM_2.5, PM₁₀, NO₂, and SO₂, the RRs were 1.18 (95% CI: 1.06, 1.34), 1.12 (95% CI, 1.04-1.20), 1.15 (95% CI: 1.02, 1.30), and 1.92 (95% CI: 1.18, 3.11) on lag day 3, lag day 3, lag day 0, and lag day 3, respectively. In two-pollutant model combined with PM_2.5 and PM₁₀, a statistically significant increase in spontaneous abortion incidence of 18.0% (RR = 1.18, 95% CI: 1.06, 1.32) was found for a 20 μg/m³ increase in PM_2.5 exposure, and 11.2% (RR = 1.11, 95% CI: 1.03, 1.20) for a 20 μg/m³ increase in PM₁₀ exposure on lag day 3, similar to single-pollutant model analysis.

CONCLUSION

Maternal exposure to high levels of PM_2.5, PM₁₀, NO₂, and SO₂ during pregnancy may increase the risk of spontaneous abortion for acute effects and lag effects. Further research to explore sensitive exposure time windows is needed.

Outdoor Air Pollution and Pregnancy Loss: a Review of Recent Literature

Purpose of Review

This review summarizes recent literature about the impacts of outdoor air pollution on pregnancy loss (spontaneous abortion/miscarriage and stillbirth), identifies challenges and opportunities, and provides recommendations for actions.

Recent Findings

Both short- and long-term exposures to ubiquitous air pollutants, including fine particulate matter < 2.5 and < 10 μm, may increase pregnancy loss risk. Windows of susceptibility include the entire gestational period, especially early pregnancy, and the week before event. Vulnerable subpopulations were not consistently explored, but some evidence suggests that pregnant parents from more disadvantaged populations may be more impacted even at the same exposure level.

Summary

Given environmental conditions conductive to high air pollution exposures become more prevalent as the climate shifts, air pollution’s impacts on pregnancy is expected to become a growing public health concern. While awaiting larger preconception studies to further understand causal impacts, multi-disciplinary efforts to minimize exposures among pregnant women are warranted.

Impact of Environmental Pollution on Female Reproduction

The increased pollution in the world atmosphere is a global concern. Water, air, and soil are polluted by various sources, such as farm fertilizer, sewage industrial waste products, fumes, and plastics, which in turn impact human health. Plastics and other mixtures of waste affect live in the water. Moreover, the ecosystem is disrupted by the use of heavy metal-containing chemicals in agriculture, and those are eventually consumed by humans. The consequences are a significant negative impact on health including reproductive health, which impairs fertility in the human population. Reproductive functions are severely affected by different chemicals which may interfere with hormonal functions. Greater consequences are faced by the women as the number of germ cells present in the ovary is fixed during fetal life, and which are nonrenewable. From the production of ovum to fertilization, to implantation, and finally continuation of pregnancy, all are affected by the heavy metals and endocrine disruptors. Lifestyle modifications such as consumption of organic foods, plastic product avoidance, separation of residential areas from industrial/agricultural areas, proper waste disposal, and so on, may help to improve the situation.

Ambient Air Pollution Exposure Assessments in Fertility Studies: a Systematic Review and Guide for Reproductive Epidemiologists

Purpose of Review

We reviewed the exposure assessments of ambient air pollution used in studies of fertility, fecundability, and pregnancy loss.

Recent Findings

Comprehensive literature searches were performed in the PUBMED, Web of Science, and Scopus databases. Of 168 total studies, 45 met the eligibility criteria and were included in the review. We find that 69% of fertility and pregnancy loss studies have used one-dimensional proximity models or surface monitor data, while only 35% have used the improved models, such as land-use regression models (4%), dispersion/chemical transport models (11%), or fusion models (20%). No published studies have used personal air monitors.

Summary

While air pollution exposure models have vastly improved over the past decade from a simple, one-dimensional distance or air monitor data to models that incorporate physiochemical properties leading to better predictive accuracy, precision, and increased spatiotemporal variability and resolution, the fertility literature has yet to fully incorporate these new methods. We provide descriptions of each of these air pollution exposure models and assess the strengths and limitations of each model, while summarizing the findings of the literature on ambient air pollution and fertility that apply each method.

Association between Maternal Exposure to Ambient Air Pollution and the Risk of Preterm Birth: A Birth Cohort Study in Chongqing, China, 2015-2020

Recent study results on the association between maternal exposure to ambient air pollution with preterm birth have been inconsistent. The sensitive window of exposure and influence level of air pollutants varied greatly. We aimed to explore the association between maternal exposure to ambient air pollutants and the risk of preterm birth, and to estimate the sensitive exposure time window. A total of 572,116 mother–newborn pairs, daily concentrations of air pollutants from nearest monitoring stations were used to estimate exposures for each participant during 2015–2020 in Chongqing, China. We applied a generalized additive model and estimated RRs and 95% CIs for preterm birth in each trimester and the entire pregnancy period. In the single-pollutant model, we observed that each 10 μg/m³ increase in PM_2.5 had a statistically significant effect on the third trimester and entire pregnancy, with RR = 1.036 (95% CI: 1.021, 1.051) and RR = 1.101 (95% CI: 1.075, 1.128), respectively. Similarly, for each 10 μg/m³ increase in PM₁₀, there were 2.7% (RR = 1.027, 95% CI: 1.016, 1.038) increase for PTB on the third trimester, and 3.8% (RR = 1.038, 95% CI: 1.020, 1.057) increase during the whole pregnancy. We found that for each 10 mg/m³ CO increases, the relative risk of PTB increased on the first trimester (RR = 1.081, 95% CI: 1.007, 1.162), second trimester (RR = 1.116, 95% CI: 1.035, 1.204), third trimester (RR = 1.167, 95% CI: 1.090, 1.250) and whole pregnancy (RR = 1.098, 95% CI: 1.011, 1.192). No statistically significant RR was found for SO₂ and NO₂ on each trimester of pregnancy. Our study indicates that maternal exposure to high levels of PM_2.5 and PM₁₀ during pregnancy may increase the risk for preterm birth, especially for women at the late stage of pregnancy. Statistically increased risks of preterm birth were associated with CO exposure during each trimester and entire pregnancy. Reducing exposure to ambient air pollutants for pregnant women is clearly necessary to improve the health of infants.

Observable variations in human sex ratio at birth

The human sex ratio at birth (SRB), defined as the ratio between the number of newborn boys to the total number of newborns, is typically slightly greater than 1/2 (more boys than girls) and tends to vary across different geographical regions and time periods. In this large-scale study, we sought to validate previously-reported associations and test new hypotheses using statistical analysis of two very large datasets incorporating electronic medical records (EMRs). One of the datasets represents over half (∼ 150 million) of the US population for over 8 years (IBM Watson Health MarketScan insurance claims) while another covers the entire Swedish population (∼ 9 million) for over 30 years (the Swedish National Patient Register). After testing more than 100 hypotheses, we showed that neither dataset supported models in which the SRB changed seasonally or in response to variations in ambient temperature. However, increased levels of a diverse array of air and water pollutants, were associated with lower SRBs, including increased levels of industrial and agricultural activity, which served as proxies for water pollution. Moreover, some exogenous factors generally considered to be environmental toxins turned out to induce higher SRBs. Finally, we identified new factors with signals for either higher or lower SRBs. In all cases, the effect sizes were modest but highly statistically significant owing to the large sizes of the two datasets. We suggest that while it was unlikely that the associations have arisen from sex-specific selection mechanisms, they are still useful for the purpose of public health surveillance if they can be corroborated by empirical evidences.

The human sex ratio at birth (SRB), usually slightly greater than 1/2, have been reported to vary in response to a wide array of exogenous factors. In the literature, many such factors have been posited to be associated with higher or lower SRBs, but the studies conducted so far have focused on no more than a few factors at a time and used far smaller datasets, thus prone to generating spurious correlations. We performed a series of statistical tests on 2 large, country-wide health datasets representing the United States and Sweden to investigate associations between putative exogenous factors and the SRB, and were able to validate a set of previously-reported associations while also discovering new signals. We propose to interpret these results simply as public health indicators awaiting further empirical confirmation rather than as implicated in (adaptive) sexual selection mechanisms.

Chemical pollution: A growing peril and potential catastrophic risk to humanity

Anthropogenic chemical pollution has the potential to pose one of the largest environmental threats to humanity, but global understanding of the issue remains fragmented. This article presents a comprehensive perspective of the threat of chemical pollution to humanity, emphasising male fertility, cognitive health and food security. There are serious gaps in our understanding of the scale of the threat and the risks posed by the dispersal, mixture and recombination of chemicals in the wider environment. Although some pollution control measures exist they are often not being adopted at the rate needed to avoid chronic and acute effects on human health now and in coming decades. There is an urgent need for enhanced global awareness and scientific scrutiny of the overall scale of risk posed by chemical usage, dispersal and disposal.

Periconception air pollution, metabolomic biomarkers, and fertility among women undergoing assisted reproduction

BACKGROUND

Air pollution exposure has been linked with diminished fertility. Identifying the metabolic changes induced by periconception air pollution exposure among women could enhance our understanding of the potential biological pathways underlying air pollution's reproductive toxicity.

OBJECTIVE

To identify serum metabolites associated with periconception air pollution exposure and evaluate the extent to which these metabolites mediate the association between air pollution and live birth.

METHODS

We included 200 women undergoing a fresh assisted reproductive technology (ART) cycle at Massachusetts General Hospital Fertility Center (2005-2015). A serum sample was collected during stimulation, and untargeted metabolic profiling was conducted using liquid chromatography with ultra-high-resolution mass spectrometry. Exposure to nitrogen dioxide (NO₂), ozone (O₃), fine particulate matter <2.5 µm (PM_2.5), and black carbon (BC) was estimated using validated spatiotemporal models. Multivariable linear regression models were used to evaluate the associations between the air pollutants, live birth, and metabolic feature intensities. A meet in the middle approach was used to identify overlapping features and metabolic pathways.

RESULTS

From the C18 and HILIC chromatography columns, 10,803 and 12,968 metabolic features were extracted. There were 190 metabolic features and 18 pathways that were significantly associated with both air pollution and live birth (P < 0.05) across chromatography columns. Eight features were confirmed metabolites implicated in amino acid and nutrient metabolism with downstream effects on oxidative stress and inflammation. Six confirmed metabolites fell into two intuitive clusters - "antioxidants" and "oxidants"- which could potentially mediate some of the association between air pollution and lower odds of live birth. Tryptophan and vitamin B3 metabolism were common pathways linking air pollution exposure to decreased probability of live birth.

CONCLUSION

Higher periconception air pollution exposure was associated with metabolites and biologic pathways involved in inflammation and oxidative stress that may mediate the observed associations with lower probability of live birth following ART.

Short-term ambient nitrogen dioxide exposure is associated with increased risk of spontaneous abortion: A hospital-based study

There are increasing concerns with regard to spontaneous abortion (SAB), the loss of pregnancy without external intervention before 20 weeks of gestation, among reproductive-aged women. To date, limited evidence is available concerning the association between SAB and air pollutants, especially in developing countries. Daily baseline outpatient data for SAB from January 1, 2014, to December 31, 2018 (1826 days) were obtained in Chongqing, a metropolis of southwest China. The over-dispersed Poisson generalized additive model with control of meteorological conditions and day of week was used to estimate the short-term effects of ambient air pollution on the daily number of SAB outpatients. A total of 42,334 SAB outpatient visits for SAB were recorded. No statistically significant association was observed between SAB and CO, PM2.5, PM10, O3, and SO2. The positive association only appeared for NO2: positive associations between SAB and NO2 were observed in both single-day models (lag 0, lag 1, lag 3, and lag 4) and cumulative exposure models (lag 01, lag 03, and lag 05) and the most significant effects were observed at lag 05 (3.289%; 95% CI: 1.568%, 5.011%). Moreover, the women with higher ages (30-39 and > 39) were more sensitive than those with lower ages (18-29), and the effect estimates were more evident in cool seasons. Collectively, our results suggested that short-term NO2 exposure was associated with higher risk of SAB, especially in elder women and cool seasons, which may contribute to further understand the role of air pollution on SAB and other adverse obstetric outcomes.

Association of maternal exposure to ambient particulate pollution with incident spontaneous pregnancy loss

BACKGROUND

Maternal exposure to ambient fine particulate matter (PM2.5) is a potential risk factor for pregnancy loss, but the extant findings are inconsistent. One reason for the inconsistency is the difficulty of distinguishing spontaneous from induced pregnancy losses, particularly in countries with planning policies.

OBJECTIVE

To examine the association between maternal PM2.5 exposure and spontaneous incident pregnancy loss in China.

METHODS

A total of 18,513 women of reproductive age was recruited from Jiangsu Province, China, in 2007. Among them, 2451 women reported 2613 valid records of incident pregnancies from 2007 to 2010. We used Cox regression to link the outcomes (live birth, spontaneous pregnancy loss, or induced abortion) of those incident pregnancies with maternal PM2.5 exposures, assessed using well-developed estimates of historical concentrations at the county level.

RESULTS

Among the 2613 incident pregnancies, 69 spontaneous pregnancy losses, 596 induced abortions, and 1948 live births occurred. According to the adjusted model, each 10-μg/m3 increment in the average PM2.5 concentration during pregnancy was associated with a 43.3% (95% confidence interval, 6.6-92.5%) increased probability of spontaneous pregnancy loss. Advanced maternal age, a potential competing risk factor, weakened the association between PM2.5 and spontaneous pregnancy loss. The association was nonsignificant for unintended pregnancies.

CONCLUSION

Maternal PM2.5 exposure was associated significantly with incident spontaneous pregnancy loss. Our findings provide insight into the harmful effect of air pollution on human reproduction.

Miscarriage matters: the epidemiological, physical, psychological, and economic costs of early pregnancy loss

Miscarriage is generally defined as the loss of a pregnancy before viability. An estimated 23 million miscarriages occur every year worldwide, translating to 44 pregnancy losses each minute. The pooled risk of miscarriage is 15·3% (95% CI 12·5-18·7%) of all recognised pregnancies. The population prevalence of women who have had one miscarriage is 10·8% (10·3-11·4%), two miscarriages is 1·9% (1·8-2·1%), and three or more miscarriages is 0·7% (0·5-0·8%). Risk factors for miscarriage include very young or older female age (younger than 20 years and older than 35 years), older male age (older than 40 years), very low or very high body-mass index, Black ethnicity, previous miscarriages, smoking, alcohol, stress, working night shifts, air pollution, and exposure to pesticides. The consequences of miscarriage are both physical, such as bleeding or infection, and psychological. Psychological consequences include increases in the risk of anxiety, depression, post-traumatic stress disorder, and suicide. Miscarriage, and especially recurrent miscarriage, is also a sentinel risk marker for obstetric complications, including preterm birth, fetal growth restriction, placental abruption, and stillbirth in future pregnancies, and a predictor of longer-term health problems, such as cardiovascular disease and venous thromboembolism. The costs of miscarriage affect individuals, health-care systems, and society. The short-term national economic cost of miscarriage is estimated to be £471 million per year in the UK. As recurrent miscarriage is a sentinel marker for various obstetric risks in future pregnancies, women should receive care in preconception and obstetric clinics specialising in patients at high risk. As psychological morbidity is common after pregnancy loss, effective screening instruments and treatment options for mental health consequences of miscarriage need to be available. We recommend that miscarriage data are gathered and reported to facilitate comparison of rates among countries, to accelerate research, and to improve patient care and policy development.

Dietary Antioxidants in the Treatment of Male Infertility: Counteracting Oxidative Stress

Infertility affects about 15% of the population and male factors only are responsible for ~25-30% of cases of infertility. Currently, the etiology of suboptimal semen quality is poorly understood, and many environmental and genetic factors, including oxidative stress, have been implicated. Oxidative stress is an imbalance between the production of free radicals, or reactive oxygen species (ROS), and the capacity of the body to counteract their harmful effects through neutralization by antioxidants. The purpose of this review, by employing the joint expertise of international researchers specialized in nutrition and male fertility areas, is to update the knowledge about the reproductive consequences of excessive ROS concentrations and oxidative stress on the semen quality and Assisted Reproduction Techniques (ART) clinical outcomes, to discuss the role of antioxidants in fertility outcomes, and finally to discuss why foods and dietary patterns are more innocuous long term solution for ameliorating oxidative stress and therefore semen quality results and ART fertility outcomes. Since this is a narrative review and not a systematic/meta-analysis, the summarized information in the present study should be considered cautiously.

Inferential challenges when assessing racial/ethnic health disparities in environmental research

Numerous epidemiologic studies have documented environmental health disparities according to race/ethnicity (R/E) to inform targeted interventions aimed at reducing these disparities. Yet, the use of R/E under the potential outcomes framework implies numerous underlying assumptions for epidemiologic studies that are often not carefully considered in environmental health research. In this commentary, we describe the current state of thinking about the interpretation of R/E variables in etiologic studies. We then discuss how such variables are commonly used in environmental epidemiology. We observed three main uses for R/E: i) as a confounder, ii) as an effect measure modifier and iii) as the main exposure of interest either through descriptive analysis or under a causal framework. We identified some common methodological concerns in each case and provided some practical solutions. The use of R/E in observational studies requires particular cautions in terms of formal interpretation and this commentary aims at providing a practical resource for future studies assessing racial/ethnic health disparities in environmental research.

Ambient air pollution and risk of pregnancy loss among women undergoing assisted reproduction

Accumulating evidence suggests that air pollution increases pregnancy loss; however, most previous studies have focused on case identification from medical records, which may underrepresent early pregnancy losses. Our objective was to investigate the association between acute and chronic exposure to ambient air pollution and time to pregnancy loss among women undergoing assisted reproductive technologies (ART) who are closely followed throughout early pregnancy. We included 275 women (345 human chorionic gonadotropin (hCG)-confirmed pregnancies) undergoing ART at a New England academic fertility center. We estimated daily nitrogen dioxide (NO₂), ozone (O₃), fine particulate matter <2.5 μm (PM_2.5), and black carbon (BC) exposures using validated spatiotemporal models estimated from first positive hCG test until day of failure or live birth. Air pollution exposures were averaged over the past week and the whole pregnancy. Multivariable Cox proportional hazards models were used to estimate the hazards ratio (HR) for pregnancy loss for an interquartile range (IQR) increase in pollutant exposure. We tested for violation of proportional hazards by considering an interaction between time (in days) since positive hCG (<30 days vs. ≥30 days) and air pollution. The incidence of pregnancy loss was 29 per 100 confirmed pregnancies (n = 99). Among pregnancies not resulting in live birth, the median (IQR) time to loss was 21 (11, 30) days following positive hCG. Average past week exposures to NO₂, O₃, PM_2.5, and BC were not associated with time to pregnancy loss. Exposure throughout pregnancy to NO₂ was not associated with pregnancy loss; however, there was a statistically significant interaction with time (p-for-interaction<0.001). Specifically, an IQR increase in exposure to NO₂ was positively associated with pregnancy loss after 30 days (HR = 1.34, 95% CI: 1.13, 1.58), but not in the first 30 days after positive hCG (HR = 0.83, 95% CI: 0.57, 1.20). Overall pregnancy exposure to O₃, PM_2.5, and BC were not associated with pregnancy loss regardless of timing. Models evaluating joint effects of all pollutants yielded similar findings. In conclusion, acute and chronic exposure to NO₂, O₃, PM_2.5, and BC were not associated with risk of pregnancy loss; however, higher exposure to NO₂ throughout pregnancy was associated with increased risk of loss 30 days after positive hCG. In this cohort, later pregnancy losses appeared more susceptible to the detrimental effects of air pollution exposure.

Human Health and Economic Costs of Air Pollution in Utah: An Expert Assessment

Air pollution causes more damage to health and economy than previously understood, contributing to approximately one in six deaths globally. However, pollution reduction policies remain controversial even when proven effective and cost negative, partially because of misunderstanding and growing mistrust in science. We used an expert assessment to bridge these research–policy divides in the State of Utah, USA, combining quantitative estimates from 23 local researchers and specialists on the human health and economic costs of air pollution. Experts estimated that air pollution in Utah causes 2480 to 8000 premature deaths annually (90% confidence interval) and decreases the median life expectancy by 1.1 to 3.6 years. Economic costs of air pollution in Utah totaled $0.75 to $3.3 billion annually, up to 1.7% of the state’s gross domestic product. Though these results were generally in line with available estimates from downscaled national studies, they were met with surprise in the state legislature, where there had been an almost complete absence of quantitative health and economic cost estimates. We discuss the legislative and personal responses of Utah policy makers to these results and present a framework for increasing the assimilation of data into decision making via regional expert assessment. In conclusion, combining quantitative assessments from local experts is a responsive and cost-effective tool to increase trust and information uptake during time-sensitive policy windows.

Nitrogen dioxide exposure during pregnancy and risk of spontaneous abortion: a case-control study in China

BACKGROUND

Evidence on the relationship between prenatal exposure to NO₂ and CO and spontaneous abortion (SAB) is insufficient. We investigated whether there is an association between maternal exposure to nitrogen dioxide (NO₂) and carbon monoxide (CO) before and during pregnancy and SAB.

METHODS

We conducted a case-control study using medical records of 2445 pregnant women who admitted for abortion prior to 20 weeks of gestational age from January 2014 to December 2019 at a tertiary-care hospital in Shanghai, China. Of the 2445 participants, 1075 were SAB cases and 1370 were healthy controls (underwent elective abortions). Maternal exposure to NO₂ and CO before and during pregnancy was estimated using daily air pollution concentration data. Multivariable logistic regression models were constructed to quantify the relationships between maternal exposure to NO₂ or CO and the risk of SAB while controlling for potential confounders.

RESULTS

NO₂ exposure levels during pregnancy were significantly higher in SAB cases than in healthy controls (42.26 vs. 40.67, p < .01). NO₂ exposure during pregnancy was positively associated with the risk of SAB. An interquartile range (16 μg/m³) increase in NO₂ exposure was associated with 68% increase in the odds of SAB (OR = 1.68, 95% CI, 1.28, 2.21). Analyses of associations by quartile of NO₂ exposure showed that elevated NO₂ exposure during pregnancy was associated with increased odds of SAB in linear dose-response manners. Compared with the lowest quartile of NO₂ exposure, the odds of SAB in the fourth quartile of NO₂ exposure increased 61% (OR = 1.61, 95% CI, 1.03-2.53). No associations of CO exposure with SAB risk were observed.

CONCLUSIONS

Our study suggested that exposure to NO₂ during early pregnancy was associated with increased risk of SAB. Further studies are needed to confirm our results and explore the potential biological mechanism underlying these associations.

Prenatal exposure to ambient air pollution and adverse pregnancy outcomes in Ahvaz, Iran: a generalized additive model

OBJECTIVE

There is some evidence about the short-term effects of air pollutants on adverse pregnancy outcomes. The aim of this study was to determine the association between air pollutants and spontaneous abortion, stillbirth, gestational hypertension, preeclampsia, gestational diabetes and macrosomia in Ahvaz, which is one of the most polluted cities in the Middle East.

METHODS

Data on adverse pregnancy outcomes and air pollutants including ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), carbon monoxide (CO), particles with a diameter of less than 10 µm (PM₁₀) and particles with a diameter less than 2.5 µm (PM_2.5) were inquired from the Health Department of Ahvaz Jundishapur University of Medical Sciences and the Environmental Protection Agency of Khuzestan Province for the years 2008-2018. A time series analysis using the generalized additive model (GAM) with up to 6-day lags was used.

RESULTS

The results showed that the SO₂ pollutant on 0, 1, 3, 4, and 6-day lags and PM₁₀ on lag 0 had direct and significant associations with spontaneous abortion. NO, NO₂ and CO on 0-6-day lags, and O₃ on 6-day lags showed direct and significant associations with preeclampsia. NO and NO₂ pollutants showed significant and direct associations with gestational diabetes, during 0- and 6-day lags. NO on 0-, 3- and 4-day lags, CO in all 0-6-day lags and PM_2.5 on 1-, 3-, 5-, and 6-day lags showed direct and significant associations with macrosomia. None of the pollutants showed significant associations with stillbirth or gestational hypertension.

CONCLUSIONS

The results of this study suggest that some air pollutants are associated with spontaneous abortion, preeclampsia, gestational diabetes and macrosomia. This study further emphasizes the need to control ambient air pollution.

Sporadic pregnancy loss and recurrent miscarriage

Progesterone is essential for the maintenance of pregnancy, and progesterone deficiency is associated with miscarriage. The subject of whether progesterone supplementation in early pregnancy can prevent miscarriage has been a long-standing research question and has been investigated and debated in the medical literature for over 70 years. During this time, several different progestogens have been synthesised and tested for the prevention of miscarriage. In this chapter, we describe the prior evidence alongside the latest research using micronized natural progesterone as well as synthetic progestogens, which were used to treat both recurrent and threatened miscarriage. The totality of evidence indicates that women with a past history of miscarriage who present with bleeding in early pregnancy may benefit from the use of vaginal micronized progesterone. The clinical implications of the findings are discussed.

The short-term effects of air pollution on respiratory disease hospitalizations in 5 cities in Poland: comparison of time-series and case-crossover analyses

Very few publications have compared different study designs investigating the short-term effects of air pollutants on healthcare visits and hospitalizations for respiratory tract diseases. This study describes, using two different study designs (a case-crossover design and a time-series analysis), the association of air pollutants and respiratory disease hospitalizations. The study has been conducted on 5 cities in Poland on a timeline of almost 4 years. DLNM and regression models were both used for the assessment of the short-term effects of air pollution peaks on respiratory hospitalizations. Both case-crossover and time-series studies equally revealed a positive association between air pollution peaks and hospitalization occurrences. Results were provided in the form of percentage increase of a respiratory visit/hospitalization, for each 10-μg/m3 increment in single pollutant level for both study designs. The most significant estimated % increases of hospitalizations linked to increase of 10 μg/m3 of pollutant have been recorded in general with particulate matter, with highest values for 24 h PM2.5 in Warsaw (6.4%, case-crossover; 4.5%, time series, respectively) and in Białystok (5.6%, case-crossover; 4.5%, time series, respectively). The case-crossover analysis results have shown a larger CI in comparison to the results of the time-series analysis, while the lag days were easier to identify with the case-crossover design. The trends and the overlap of the results occurring from both methods are good and show applicability of both study designs to air pollution effects on short-term hospitalizations.

Before the beginning: environmental exposures and reproductive and obstetrical outcomes

There is growing consensus that preconception exposure to environmental toxins can adversely affect fertility, pregnancy, and fetal development, which may persist into the neonatal and adult periods and potentially have multigenerational effects. Here we review current data on preconception and prenatal exposure to several chemicals, including heavy metals, endocrine-disrupting chemicals, pesticides, and air pollution, and their associated obstetrical and reproductive health effects. Reproductive endocrinologists and affiliated health care providers have a unique opportunity to counsel patients before they get pregnant to minimize exposure to hazardous chemicals with the goal to improve reproductive outcomes and assure a healthy lifestyle overall. We provide practical tools and some publicly available resources for reproductive health professionals to assess a patient's risks and ways to reduce chemical and air pollution exposures during the critical preconception and prenatal periods.

Air Pollution and Health - A Science-Policy Initiative

Air pollution is a major, preventable and manageable threat to people's health, well-being and the fulfillment of sustainable development. Air pollution is estimated to contribute to at least 5 million premature deaths each year across the world. No one remains unaffected by dirty air, but the adverse impacts of air pollution fall most heavily upon vulnerable populations, such as children, women, and people living in poverty - groups to whom States have special obligations under international human rights law. The National Academies of Sciences and Medicine of South Africa, Brazil, Germany and the United States of America are calling upon government leaders, business and citizens to take urgent action on reducing air pollution throughout the world - to the benefit of human health and well-being, to the benefit of the environment and as a condition towards sustainable development. Air pollution is a cross-cutting aspect of many UN Sustainable Development Goals.

Air pollution exposure and risk of spontaneous abortion in the Nurses' Health Study II

STUDY QUESTION

Is there an association between air pollution exposures and the risk of spontaneous abortion (SAB)?

SUMMARY ANSWER

Higher exposure to particulate matter (PM) air pollution above and beyond a woman's average exposure may be associated with greater risk of SAB, particularly among women experiencing at least one SAB during follow-up.

WHAT IS KNOWN ALREADY

There is sufficient biologic plausibility to suggest that air pollution adversely affects early pregnancy outcomes, particularly pregnancy loss; however, the evidence is limited.

STUDY DESIGN, SIZE, DURATION

Our prospective cohort study included 19 309 women in the Nurses' Health Study II who contributed a total of 35 025 pregnancies between 1990 and 2008. We also conducted a case-crossover analysis among 3585 women (11 212 pregnancies) with at least one SAB and one live birth during follow-up.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Proximity to major roadways and exposure to PM <10 microns (PM10), 2.5-10 microns (PM2.5-10) and <2.5 microns (PM2.5) were determined for residential addresses between 1989 and 2007. Pregnancy outcomes were self-reported biannually throughout follow-up and comprehensively in 2009. Multivariable log-binomial regression models with generalized estimating equations were used to estimate the risk ratios and 95% CIs of SAB. Conditional logistic regression was used for the case-crossover analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

During the 19 years of follow-up, 6599 SABs (18.8% of pregnancies) were reported. In the main analysis, living closer to a major roadway and average exposure to PM10, PM10-2.5 or PM2.5 in the 1 or 2 years prior to pregnancy were not associated with an increased risk of SAB. However, small positive associations between PM exposures and SAB were observed when restricting the analysis to women experiencing at least one SAB during follow-up. In the case-crossover analysis, an increase in PM10 (per 3.9 μg/m3), PM2.5-10 (per 2.3 μg/m3) and PM2.5 (per 2.0 μg/m3) in the year prior to pregnancy was associated with 1.12 (95% CI 1.06, 1.19), 1.09 (95% CI 1.03, 1.14) and 1.10 (95% CI 1.04, 1.17) higher odds of SAB, respectively.

LIMITATIONS, REASONS FOR CAUTION

We did not have information on the month or day of SAB, which precluded our ability to examine specific windows of susceptibility or acute exposures. We also used ambient air pollution exposures as a proxy for personal exposure, potentially leading to exposure misclassification.

WIDER IMPLICATIONS OF THE FINDINGS

In our case-crossover analysis (but not in the entire cohort) we observed positive associations between exposure to all size fractions of PM exposure and risk of SAB. This may suggest that changes in PM exposure confer greater risk of SAB or that women with a history of SAB are a particularly vulnerable subgroup.

STUDY FUNDING/COMPETING INTEREST(S)

The authors are supported by the following NIH grants UM1CA176726, R00ES026648 and P30ES000002. The authors have no actual or potential competing financial interests to disclose.