Third trimester as the susceptibility window for maternal PM2.5 exposure and preterm birth: A nationwide surveillance-based association study in China

Examining modification of the associations between air pollution and birth outcomes by neighborhood deprivation in a North Carolina birth cohort, 2011-2015

Background

Evidence from studies of air pollutants and birth outcomes suggests an association, but uncertainties around geographical variability and modifying factors still remain. As neighborhood-level social characteristics are associated with birth outcomes, we assess whether neighborhood deprivation level is an effect measure modifier on the association between air pollution and birth outcomes in a North Carolina birth cohort.

Methods

Using birth certificate data, all North Carolina residential singleton live births from 1 January 2011 to 31 December 2015 with gestational ages of 20-44 weeks (n = 566,799) were examined for birth defect diagnoses and preterm birth. Exposures were daily average fine particulate matter (PM2.5), daily 8-h maximum nitrogen dioxide (NO2), and daily 8-h maximum ozone (O3) modeled concentrations, and the modifier of interest was the neighborhood deprivation index (NDI). Linear binomial models were used to estimate the prevalence differences and 95% confidence intervals (CI) for the association between ambient air pollution and birth defect diagnoses. Modified Poisson regression models were used to estimate risk differences (RDs) and 95% CIs for air pollution and preterm birth. Models were stratified by the neighborhood deprivation index group (low, medium, or high) to assess potential modification by NDI.

Results

Approximately 3.1% of the study population had at least one birth defect and 8.18% were born preterm. For preterm birth, associations with PM2.5 and O3 did not follow a conclusive pattern and there was no evidence of modification by NDI. The associations between NO2 and preterm birth were generally negative across exposure windows except for a positive association with NO2 and preterm birth for high NDI [RD: 34.70 (95% CI 4.84-64.56)] for entire pregnancy exposure. There was no evidence of associations between pollutants examined and birth defects.

Conclusions

There may be differences in the association between NO2 exposure and preterm birth by NDI but we did not observe any evidence of associations for birth defects. Our results support the public health protection afforded by reductions in air pollution, even in areas of neighborhood deprivation, but future research conducted in areas with higher levels of air pollution and evaluating the potential for modification by neighborhood deprivation level would be informative.

Prevalence of congenital cryptorchidism in China: A nationwide population-based surveillance study, 2007-2021

BACKGROUND

Despite cryptorchidism being a common genital abnormality in male newborns with significant prevalence variations globally, there is a notable scarcity of epidemiological data on this condition in China.

OBJECTIVE

This study aimed to delineate the prevalence pattern of cryptorchidism in Chinese population over the past 15 years using nationwide surveillance data.

MATERIALS AND METHODS

Data from the China National Population-based Birth Defects Surveillance System (2007-2021) were analyzed to calculate the prevalence rates of cryptorchidism, stratified by birth year, maternal age, maternal residence, and geographic region. Adjusted prevalence rate ratios were computed using Poisson regression, while trends in prevalence and average annual percent change (AAPC) were assessed using the joinpoint regression model.

RESULTS

During the study period, a total of 1,833 cases of cryptorchidism were identified among 2,565,964 full-term male births, resulting in prevalence rates of 7.14, 5.60, and 1.54 per 10,000 births for overall, isolated, and associated cryptorchidism, respectively. The overall prevalence increased from 3.86 to 11.20 per 10,000 births, with an AAPC of 7.9% (95% confidence interval: 5.5-11.0). Significant variations were observed across maternal age (< 20 years, 7.62/10,000; 20-24 years, 6.14/10,000; 25-29 years, 6.96/10,000; 30-34 years, 7.48/10,000; ≥35 years, 9.22/10,000), maternal residence (urban vs. rural, 10.99/10,000 vs. 2.86/10,000), and geographic region (eastern, 12.38/10,000; central, 2.36/10,000; western, 2.63/10,000). Approximately one-third of cryptorchidism cases were bilaterally, while two-thirds were unilateral. Commonly observed associated abnormalities included congenital hydrocele testis, as well as anomalies in the genital organs, circulatory system, and musculoskeletal system.

CONCLUSION

Despite lower rates compared to other countries, the increasing trend in prevalence of cryptorchidism necessitates further investigation and intervention.

Association between risk of preterm birth and long-term and short-term exposure to ambient carbon monoxide during pregnancy in chongqing, China: a study from 2016-2020

BACKGROUND

Preterm birth (PTB) is an important predictor of perinatal morbidity and mortality. Previous researches have reported a correlation between air pollution and an increased risk of preterm birth. However, the specific relationship between short-term and long-term exposure to carbon monoxide (CO) and preterm birth remains less explored.

METHODS

A population-based study was conducted among 515,498 pregnant women in Chongqing, China, to assess short-term and long-term effects of CO on preterm and very preterm births. Generalized additive models (GAM) were applied to evaluate short-term effects, and exposure-response correlation curves were plotted after adjusting for confounding factors. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using COX proportional hazard models to estimate the long-term effect.

RESULTS

The daily incidence of preterm and very preterm birth was 5.99% and 0.41%, respectively. A positive association between a 100 µg/m³ increase in CO and PTB was observed at lag 0-3 days and 12-21 days, with a maximum relative risk (RR) of 1.021(95%CI: 1.001-1.043). The exposure-response curves (lag 0 day) revealed a rapid increase in PTB due to CO. Regarding long-term exposure, positive associations were found between a 100 µg/m3 CO increase for each trimester(Model 2 for trimester 1: HR = 1.054, 95%CI: 1.048-1.060; Model 2 for trimester 2: HR = 1.066, 95%CI: 1.060-1.073; Model 2 for trimester 3: HR = 1.007, 95%CI: 1.001-1.013; Model 2 for entire pregnancy: HR = 1.080, 95%CI: 1.073-1.088) and higher HRs of very preterm birth. Multiplicative interactions between air pollution and CO on the risk of preterm and very preterm birth were detected (P- interaction<0.05).

CONCLUSIONS

Our findings suggest that short-term exposure to low levels of CO may have protective effects against preterm birth, while long-term exposure to low concentrations of CO may reduce the risk of both preterm and very preterm birth. Moreover, our study indicated that very preterm birth is more susceptible to the influence of long-term exposure to CO during pregnancy, with acute CO exposure exhibiting a greater impact on preterm birth. It is imperative for pregnant women to minimize exposure to ambient air pollutants.

Joint effects of green space and air pollutant exposure on preterm birth: evidence from a nationwide study in China

An association between green space exposure and preterm birth has been reported. However, evidence on the joint effects of air pollutant and green space exposure on preterm birth from nationwide research is limited in China. Based on a nationwide cohort, this study aims to explore the effect of green space exposure on preterm birth and analyze the joint effects of green space and air pollutant. Logistic regression models were developed to analyze the effects of green space exposure, and interaction effects were evaluated by adding interaction terms between green space and air pollutants. From 2013 to 2019, this study included 2,294,188 records of newborn births, of which 82,921 were preterm births. The results show that for buffer zones with 250 m, 500 m, 1000 m, and 1500 m, every 0.1 unit increase in NDVI exposure was associated with a decrease in the risk of preterm birth by 5.5% (95% CI: 4.6-6.4%), 5.8% (95% CI: 4.9-6.6%), 6.1% (95% CI: 5.3-7.0%), and 5.6% (95% CI: 4.7-6.5%), respectively. Under high-level exposure to air pollutants, high-level NDVI exposure was more strongly negatively correlated with preterm birth than low-level NDVI exposure. High-level green space exposure might mitigate the adverse effect of air pollutants on preterm birth by promoting physical activity, reducing stress, and adsorbing pollutants. Further investigation is needed to explore how green space and air pollution interact and affect preterm birth, in order to improve risk management and provide a reference for newborn health.

Effect of a chimney-fitted improved stove on pregnancy outcomes in Northwest Ethiopia: a randomized controlled trial

BACKGROUND

Exposure to household air pollution during pregnancy has been linked to adverse pregnancy outcomes. Improved stove was implemented in Ethiopia to reduce this exposure and related health problems. However, the effects of improved stove interventions on pregnancy outcomes remains uncertain.

METHOD

Individually randomized stove replacement trial was conducted among 422 households in six low-income rural kebeles of Northwestern Ethiopia. Pregnant women without known health conditions were recruited at ≤ 24 weeks gestation and randomized to an intervention or control group with a 1:1 ratio. A baseline survey was collected and a balance test was done. Two-sided independent samples t-test for continuous outcomes and chi-square for categorical variables were used to compare the effect of the intervention between the groups. Mean differences with 95% CIs were calculated and a p-value of < 0.05 was considered statistically significant.

RESULT

In this study, the mean birth weight was 3065 g (SD = 453) among the intervention group and not statistically different from 2995 g (SD = 541) of control group. After adjusting for covariates, infants born from intervention group weighed 55 g more [95% CI: - 43 to 170) than infants born from the control group, but the difference was not statistically significant (P = 0.274). The respective percentages for low birth weight were 8% and 10.3% for intervention and control groups respectively (P = 0.346). However, the average gestational age at delivery was higher among improved stove users (38 weeks (SD = 8.2) compared to control groups 36.5 weeks (SD = 9.6) with statistically significant difference at 0.91 weeks (95% CI: 0.52 to 1.30 weeks, p < 0.001). The corresponding difference in risk ratio for preterm birth is 0.94 (95% CI:0.92 to 0.97; p < 0.001). The percentages for maternal complications, stillbirth, and miscarriage in the intervention group were not statistically different from the control group.

CONCLUSIONS

While the increase in average birth weight among babies born to mothers using improved stoves was not statistically significant, babies had a longer gestational age on average, offering valuable health benefits. However, the study didn't find a significant impact on other pregnancy outcomes like stillbirth, miscarriage, or maternal complications.

TRIAL REGISTRATION

The study was registered at the Pan African Clinical Trial Registry website under the code PACTR202111534227089, ( https://pactr.samrc.ac.za/ (Identifier). The first trial registration date was (11/11/2021).

Prenatal exposure to PM2.5 components and the risk of different types of preterm birth and the mediating effect of pregnancy complications: a cohort study

OBJECTIVES

This study aims to reveal the single and mixed associations of PM2.5 and its components with very, moderately, and late preterm births and to explore the potential mediating role of pregnancy complications in PM2.5-induced preterm birth.

STUDY DESIGN

This was a retrospective cohort study.

METHODS

We enrolled 168,852 mothers and matched the concentrations of PM2.5 and its five components (OM, SO42-, BC, NO3-, and NH4+) based on their geographical location. Next, we used generalized linear models, quantile g-computation, and mediation analysis to evaluate the associations of PM2.5 and its components with very, moderately, and late preterm births and the mediating role of pregnancy complications.

RESULTS

Prenatal exposure to PM2.5 and its components was associated with preterm birth, and the association was strongest in the third trimester. Preterm birth was associated with co-exposure to a mixture of PM2.5 components in the third trimester, and the contributions of NO3-, NH4+, and BC to the risk of preterm birth were positive. Meanwhile, pregnancy complications mediated PM2.5-induced preterm birth. Moreover, very and moderately preterm births were associated with PM2.5 and its components in the second and third trimesters, and very and late preterm births were associated with co-exposure to a mixture of PM2.5 components in the third trimester.

CONCLUSIONS

Later exposure to PM2.5 during pregnancy will cause earlier preterm birth. Targeted and positive interventions for anthropogenic sources of specific PM2.5 components and pregnancy complications are helpful for preterm birth prevention.