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Background: The existing literature evaluating the association between neonatal morbidity and migrant status presents contradictory results. The purpose of this study was to compare the risk of preterm birth (PTB) and low birth weight (LBW) among newborns from local and migrant women in China's Pearl River Delta (PRD) region. Methods: In this observational population-based study, we included all live singleton deliveries from PRD region local women and migrant women. Data were sourced from the Guangdong Medical Birth Registry Information System between Jan 1, 2014, and Dec 31, 2020. Women were categorized into three groups by maternal migrant status: local women from PRD region, migrant women from Guangdong province or from other provinces. The outcome variables that were examined included two adverse birth outcomes: PTB and LBW. The association between the risk of PTB and LBW and maternal migrant status was assessed using logistic regression. Results: During 2014–2020, 5,219,133 single live deliveries were recorded, corresponding 13.22% to local women and the rest to migrant women coming from Guangdong (53.51%) and other provinces (33.26%). PTB prevalence was highest among local women (5.79%), followed by migrant women from Guangdong (5.29%), and the lowest among migrants from other provinces (4.95%). This association did not change after including maternal age, infant sex, delivery mode, and birth season in the models. Compared to local women, migrant women from other provinces had a lower risk of LBW (4.00% vs. 4.98%, P < 0.001). The prevalence of PTB and LBW was higher among local women than migrants. The odds of delivery PTB and LBW were higher for women who were age ≥ 35. Among the three maternal migration groups, the age-LBW association displayed a typical U-shaped pattern, with those in the youngest (16–24 years) and oldest (≥ 35) age categories exhibiting the higher odds of delivering a LBW neonate. With respect to infant sex, the prevalence of PTB was significantly higher in males than females among the three maternal migration groups. An opposite trend was found for LBW, and the prevalence of LBW was higher in females among the three maternal migration groups. Conclusion: The findings of this study contribute to the understanding of the epidemiology of PTB and LBW among migrant women. Our study suggests that it is the health and robust nature of migrant mothers that predisposes them to better birth outcomes. It is important to recognize that the results of this study, while supportive of the healthy migrant effect, cannot be considered definitive without some exploration of motivation for moving and changes in lifestyle postmigration. [ABSTRACT FROM AUTHOR]

Background: Studies have reported that exposure to air pollution during pregnancy was associated with preterm birth (PTB). However, it remains unknown whether this association differs between local residents and migrants.Objective: This study aimed to differentiate the associations between maternal air pollution exposure and PTB between local residents and migrants.Methods: We established a retrospective birth cohort in seven Chinese cities in Pearl River Delta (PRD) region during 2015-2017. The mothers were included in the cohort at their first time of hospital visit for pregnancy, and the endpoint events were identified using the birth registry. The air pollution exposure was estimated based on the daily air pollution concentrations in the nearby air monitoring stations during different pregnancy periods. Cox proportional hazards models were utilized to estimate the associations between each air pollutant and PTB for different pregnancy periods.Results: Our cohort included a total of 628,439 mother-and-live-birth pairs. Among them, 308,201 women were local residents, and 320,238 were migrants. We observed stronger effects of air pollutants among the migrants than the local residents. For the exposure during the entire pregnancy, the hazard ratio (HR) among the migrants and local residents were 1.56 (95% CI: 1.50, 1.63) and 0.98 (95% CI: 0.93, 1.02) for each 10 μg/m3 increase in PM2.5, 1.32 (95% CI: 1.27, 1.39) and 1.18 (95% CI: 1.12, 1.23) for each 10 ppb increase in O3, and 1.48 (95% CI: 1.40, 1.57) and 0.99 (95% CI: 0.93, 1.05) for each 10 μg/m3 increase in SO2, respectively. Similarly higher effects were observed among the migrants for the exposures in different trimesters of pregnancy. However, the effects of NO2 were comparable between the two groups.Conclusion: Our study suggests that maternal PM2.5, O3 and SO2 exposures might be important risk factors of preterm birth, particularly among the migrants. More specific protective and education measures should be considered for the migrant pregnant women. [ABSTRACT FROM AUTHOR]

Abstract Background Previous studies have reported that maternal exposure to particles with aerodynamic diameter <2.5 μm (PM 2.5) is associated with birth outcomes. However, a multicity birth cohort study has not been conducted in China, and the attributable fraction of adverse birth outcomes due to PM 2.5 exposure remains unknown. Methods We examined associations in a birth cohort of 1,455,026 mother-and-live-birth pairs who were followed up from the first hospital visit for pregnancy until the birth of the baby during 2014–2017 in nine cites of the Pearl River Delta (PRD) region, China. The PM 2.5 exposures were estimated based on the air pollution concentrations of the nearby monitors. Cox proportional hazards regressions were employed to examine the associations. Results We found 1% (HR = 1.01; 95% CI: 1.00, 1.02), 6% (HR = 1.06; 95% CI: 1.05, 1.07), and 7% (HR = 1.07; 95% CI: 1.06, 1.08) increases in risk of PTB and 20% (HR = 1.20; 95% CI: 1.18, 1.22), 18% (HR = 1.18; 95% CI: 1.15, 1.20), and 20% (HR = 1.20; 95% CI: 1.17, 1.23) increases in risk of LBW, with each 10 μg/m3 increase in PM 2.5 from trimester 1 to trimester 3, respectively. For PTB, highest HRs were observed during trimester 3, as for LBW, stronger effect were observed during trimester 1 and trimester 3. We further estimated that 7.84% (95% CI: 6.21%, 9.50%) of PTB and 14.85% (95% CI: 13.00%, 16.61%) of the LBW cases could be attributable to PM 2.5 exposure during the third trimester. Conclusion The results indicate that maternal PM 2.5 exposure is a risk factor for both LBW and PTB, and responsible for considerable burdens of PTB and LBW in the Pearl River Delta region. Highlights • We examined the effects of PM 2.5 on preterm birth and low birth weight. • PM 2.5 exposure was found to be associated with increased risk of preterm birth. • PM 2.5 exposure was observed to be associated with increased risk of low birth weight. • Substantial burden of preterm birth and low birth weight could be attributable to PM2.5 exposure. [ABSTRACT FROM AUTHOR]

Background: A few studies have examined the association between ambient temperature and preterm birth (PTB), and the results have been inconsistent. This study explored the association between ambient temperature and PTB in Shenzhen, China.Methods: Data of daily singleton PTB, air pollution and meteorological variables from 2005 to 2011 were collected in Shenzhen. A distributed lag non-linear model (DLNM) was used to investigate the association of the low and high temperatures (1st, 5th, 95th, and 99th percentiles) with PTB.Results: The median temperature was 24.5 °C and the 1st, 5th, 95th, and 99th percentiles of daily mean temperatures were 9, 12.5, 29.9 and 30.7 °C, respectively. The prevalence of singleton PTB was 5.61 % in Shenzhen. The association between temperature and PTB was not linear. There was an immediate positive association of low temperature (1st and 5th percentiles) and a negative association of high temperature (95th and 99th percentiles) with PTB. The effect of low temperature 9 °C (1st) on PTB on the current day was stronger than that of 12.5 °C (5th), with a relative risk (RR) of 1.54 (95 % CI: 1.36-1.75) and 1.49 (95 % CI: 1.35-1.63), respectively. The cumulative RR (up to 30 days) of 9 and 12.5 °C was 1.72 (95 % CI: 1.28-2.33) and 1.96 (95 % CI: 1.60-2.39), respectively. The cumulative effects (up to 30 days) of high temperature (95th and 99th percentiles) on PTB were 0.69 (95 % CI: 0.60-0.80) and 0.62 (95 % CI: 0.52-0.74), respectively. The cumulative effect (up to 30 days) of low temperatures on vaginal delivery PTB was lower than that of the cesarean section PTB with an RR of 1.58 (95 % CI: 1.12-2.22) and 1.93 (95 % CI: 1.21-3.08), respectively.Conclusions: This study suggests that low temperature might be a risk factor, while high temperature might be a protective factor of PTB in Shenzhen. [ABSTRACT FROM AUTHOR]

Previous studies have indicated maternal exposure to particles with aerodynamic diameter <2.5 μm (PM 2.5) is associated with preterm birth (PTB). However, no study has investigated this effect in pre-pregnancy impaired fasting glucose (IFG) women. This study aimed to differentiate the effects of maternal PM 2.5 exposure on PTB between pre-pregnancy IFG and normoglycemia women, and to further identify the susceptible window. This cohort study was conducted between January 2014 and December 2017 in 21 Chinese cities. All the recruited women received pre-pregnancy fasting serum glucose (FSG) tests and were followed up for their delivery outcomes. The PM 2.5 exposures were estimated by the daily air pollution concentrations of the nearby monitors. Women with FSG below 7.0 mmol/L were included in the analysis. We employed the Cox proportional hazards models to examine whether PM 2.5 exposure was associated with PTB. 237957 women were included and 7055 (3.0%) of them were pre-pregnancy IFG. During the entire pregnancy, we found 24.1% (HR = 1.241; 95% CI: 1.069, 1.439), 61.8% (HR = 1.618; 95% CI: 1.311, 1.997) and 18.6% (HR = 1.186; 95% CI: 1.004, 1.402) of increases in risk for all PTB, early PTB (20–33 gestational weeks) and late PTB (34–36 gestational weeks) among the pre-pregnancy IFG women, and 15.9% (HR = 1.159; 95% CI: 1.127, 1.192), 33.9% (HR = 1.339; 95% CI: 1.255, 1.430) and 13.2% (HR = 1.132; 95% CI: 1.098, 1.168) of increases in risk for all PTB, early PTB and late PTB among the normoglycemia women, with each 10 μg/m3 increment of PM 2.5 exposure, respectively. Furthermore, PM 2.5 exposure had the strongest effect on all PTB during trimester 1 (0–12 gestational weeks) among the pre-pregnancy IFG women, compared with the less strong effect during trimester 1 among the normoglycemia women. In conclusion, pre-pregnancy IFG increases the risk of PTB attributed to PM 2.5 , especially during trimester 1. Moreover, the effects of PM 2.5 are greater on early PTB than late PTB for both pre-pregnancy IFG and normoglycemia women. • The first study on association of PTB with PM2.5 in pre-pregnancy IFG women. • Pre-pregnancy IFG increases the risk of PTB attributed to ambient PM2.5. • Susceptible exposure windows for pre-pregnancy IFG women is the trimester 1. • Effects of PM2.5 are greater on early PTB than late PTB for pregnancy women. [ABSTRACT FROM AUTHOR]

Maternal exposure to various air pollutants is one crucial contributor to adverse birth outcomes, however, the effects of ozone (O 3) exposure have remained largely unknown, especially attributable burden in different exposure windows. We performed a birth cohort study in nine Chinese cities in Guangdong Province during 2014–2017. The mothers were included in this study at their first time hospital visits for pregnancy in the nine cities, and followed up till the delivery. Air pollution exposure of each participant was estimated using the daily data from air monitoring stations in the mother's residential district. The status of low birth weight (LBW) and preterm birth (PTB) was ascertained based on standard criteria and collected from the electronic medical record. We applied a Cox regression model to estimate the associations and the attributable burden. Among the 1,455,026 mother-and-live-birth pairs, 64,028 (4.40%) were PTB, and 57,618 (3.96%) were LBW. After adjustment for potential confounders, the hazard ratios for each 10 μg/m3 increase in O 3 concentrations during trimester 1, trimester 2, one week prior and four weeks prior were 1.025 (95% CI: 1.020, 1.030), 1.033 (95% CI: 1.028, 1.039), 1.013 (95% CI: 1.010, 1.017) and 1.016 (95% CI: 1.011, 1.020) for PTB, 1.035 (95% CI: 1.030, 1.040), 1.035 (95% CI: 1.029, 1.041), 1.013 (95% CI: 1.009, 1.017) and 1.016 (95% CI: 1.012, 1.021) for LBW, respectively. The estimated attributable fractions at one week prior to delivery were 0.86% (95% CI: 0.39%, 9.26%) of PTB and 0.87% (95% CI: 0.60%, 1.14%) of LBW. This study indicates that maternal exposure to O 3 might lead to increased risk of PTB and LBW, and is responsible for non-negligible burden of PTB and LBW in the study region. • Maternal O 3 exposure might lead to increased risk of PTB. • Maternal O 3 exposure might lead to increased risk of LBW. • These associations were not confounded by PM 2.5 , NO 2 , and SO 2 concentrations. [ABSTRACT FROM AUTHOR]

Background: Preterm birth is the leading cause of child mortality under 5 years of age. Temporal trends in preterm birth rates are highly heterogeneous among countries and little information exists for China. To address this data gap, we investigated annual changes in preterm birth incidence rate and explored potential determinants of these changes in Shenzhen, China. Methods: A total of 1.4 million live births, during 2003-2012, were included from the Shenzhen birth registry. Negative-binominal regression models were used to estimate the annual percent changes in incidence. To identify the potential determinants behind temporal trends, we estimated the contribution of each changing risk factor to changes in rate by calculating the difference in population-attributable risk fraction. Results: Annual preterm birth incidence rates increased by 0.94% (95% CI 0.30%, 1.58%) overall, 3.60% (95% CI 2.73%, 4.48%) for medically induced, and 3.13% (95% CI 1.01%, 5.31%) for preterm premature rupture of membranes, but decreased by 2.34% (95% CI 1.62%, 3.06%) for spontaneous preterm labor. Higher maternal educational attainment (0.20 rate increase), lower proportion of inadequate prenatal care (0.15 rate reduction), more multipara (0.08 rate reduction), decreased proportion of preeclampsia or eclampsia (0.05 rate reduction), and larger proportion of young and older pregnant women (0.04 rate increase) were significant contributors to the overall change over time. Contributions of changing risk factors were different between preterm birth subtypes. Conclusions: Preterm birth rate in Shenzhen, China increased overall during 2003-2012, although trends varied across three preterm birth subtypes. The rising rates were associated with changes in maternal education and age. [ABSTRACT FROM AUTHOR]