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Abstract

Objective

Preterm birth is a major global public health issue. However, sex difference in incidence and the potential association with air pollution in these disparities have not been fully explored globally.

Methods

This study is a retrospective, cross-sectional secondary analysis based on the Global Burden of Disease (GBD) 2021 database. Indicators included incidence, disability-adjusted life years (DALYs), years of life lost (YLLs), age-standardized rates, age-standardized YLL rate, age-standardized DALY rate, age-standardized YLL percent (ASYP), and age-standardized DALY percent (ASDP). Analyses were stratified by sex, socio-demographic index (SDI), and 21 GBD regions.

Results

From 1990 to 2021, male infants consistently experienced higher rates of preterm birth and greater disease burden than females, though the male-to-female ratio gradually narrowed. Particulate matter pollution significantly contributed to the burden of preterm birth, with males experiencing a higher burden than females. In 2021, particulate matter pollution accounted for roughly 1.3 times the burden observed in females and contributed to 31.1% of male ASYP and 26.7% of ASDP. Household air pollution was a major contributor, and its impact on males and females was similar in proportional terms. Regional variation was marked, with low-SDI regions, particularly sub-Saharan Africa and South Asia, experiencing the highest burden. Sex-stratified analyses revealed that air pollution, particularly household air pollution, had a more pronounced impact on males in some regions.

Conclusions

Male infants consistently face a higher risk and burden of preterm birth worldwide. Particulate matter pollution, particularly household air pollution, appears to be linked to these disparities, especially in low-SDI regions. These findings underscore the need for targeted interventions to reduce indoor air pollution and mitigate sex-based inequalities in preterm birth burden.

Keywords

Preterm birth Sex Disease burden Global Burden of Disease particulate matter pollution

Introduction

Preterm birth is a major global public health challenge, associated with increased mortality rates and long-term impairment.^1–4 It also imposes substantial financial costs and heightens the psychological distress risk among parents.^5,6 Growing evidence indicates that, compared with females, male infants are disproportionately affected by preterm birth, exhibiting a higher incidence,^7,8 greater perinatal mortality,⁹ and an increased risk of neurodevelopmental issues.^10,11 These sex-based disparities are likely shaped not only by biological factors but also external influences, such as environmental exposures.¹²

Among environmental exposures, particulate matter pollution has been identified as a significant risk factor for adverse birth outcomes.¹³ Dadvand et al. reported that maternal exposure to particulate matter pollution during pregnancy was strongly associated with preterm premature rupture of membranes.¹⁴ Cohort studies in multiple countries confirmed this finding.^15–18 Importantly, particulate matter pollution affects not only the incidence of preterm birth but also the birth sex ratio. Research in Japan has shown that elevated concentrations of fine particulate matter (PM_2.5) were associated with a reduction in male-to-female birth ratio.¹⁹ Similarly, in Taipei, the introduction of a mass rapid transit system, which reduced PM_2.5 levels, was accompanied by changes in the birth sex ratio.²⁰ In Poland, exposure to PM_2.5 and PM₁₀ was linked to a decreased proportion of Y-chromosome-bearing sperm.²¹ Additionally, historical environmental events, such as the 1952 London smog and the “Black Saturday” bushfires in Australia, have also been related to declines in the proportion of male births.²² However, most studies are country-specific, and global data remains limited.

To address this, we used the Global Burden of Disease Study (GBD) 2021 ²³ to analyze global trend in sex differences in preterm infants from 1990 to 2021. We also assessed country-level disparities in 2021 and quantified sex-stratified preterm birth burden attributable to particulate matter pollution across five socio-demographic index (SDI) categories and 21 GBD regions. By integrating sex-specific analyses with environmental risk assessment, this study highlights high-risk populations and informs the development of targeted public health strategies.

Materials and methods

Data sources

Our study is a retrospective, cross-sectional secondary analysis based on data from the 2021 GBD study, which provides a detailed epidemiologic assessment of 371 diseases and injuries and 88 risk factors across 204 countries and 811 subnational locations spanning the years from 1990 to 2021.²⁴ Further details and original data can be accessed through the website of Global Health Data Exchange query tool (http://ghdx.healthdata.org/gbd-results-tool). The reporting of this study conforms to the STROBE guidelines.²⁵

Attributable burden of preterm birth due to particulate matter pollution

GBD classifies all GBD risk factors into a risk factor hierarchy with four levels, plus an overarching aggregate of all risk factors combined. Particulate matter pollution, belonging to level 3, was disaggregated into ambient particulate matter pollution and household air pollution from solid fuels at level 4. To analyze the attributable burden due to particulate matter pollution, relative risk (RR) estimates were first quantified by meta-regression in the burden of proof approach, utilizing distinct sources from all cohort, case-control, or randomized controlled trial studies that report RRs of mortality or morbidity from preterm labor as a function of risk exposure.²⁶ Burden of proof risk function (BPRF) methods were newly developed to evaluate potential publication or reporting bias and quantified unexplained between-study heterogeneity, complementing estimates of RR in GBD 2021.²⁴ Population attributable fraction (PAFs) were then calculated as the proportional change in health that would occur if exposure to the risk factor in the past had been at the counterfactual level of the theoretical minimum risk exposure level (TMREL) based on epidemiological evidence. Since GBD 2015, a uniform counterfactual distribution from 2.4 to 5.9 μg/m³ as TMREL was determined for both ambient and household PM_2.5.²⁷ The proportion of disease burden attributable to particulate matter pollution was finally quantified by the product of the PAF and the disability-adjusted life years (DALYs) or deaths associated with the outcome.

Definition

Age-standardized incidence rate (ASIR) is the incidence rate per 100,000 population following standardization to the global age structure, enabling comparisons across time and geography.

Years of life lost (YLLs) represent the years lost due to premature mortality, calculated by multiplying the number of deaths at each age by the standard life expectancy for that age.

Age-standardized YLL rate (ASYR) is the YLL rate per 100,000 population, adjusted to the standard population age distribution, which enables consistent comparisons of premature mortality burden across populations.

Age-standardized YLL percent (ASYP) is the proportion of the total YLL rate. It is calculated by dividing the age-standardized YLL rate attributed to air pollution by the overall ASYR of preterm birth and multiplying by 100 to express the result as a percentage.

DALYs is obtained by summing YLLs and years lived with disability. It reflects the total burden of disease, combining YLLs due to premature death and years lived with disability.

Age-standardized DALY rate (ASDR) is the DALY rate per 100,000 population, adjusted to a standard age structure to allow comparisons across populations.

Age-standardized DALY percent (ASDP) is the percentage of the total ASDR. It is calculated by dividing the age-standardized DALY rate attributable to air pollution by the overall ASDR for preterm birth, and then multiplying the result by 100 to express the result as a percentage.

SDI is a composite indicator of income, average years of schooling, and fertility for each GBD location and year. It was first developed for GBD 2015, based on the human development index methodology, which integrates life expectancy, education, and gross national income to reflect overall sociodemographic development.²⁸

Data analysis

We downloaded the absolute numbers of incidence, ASIR, DALYs, ASDR, YLLs, ASYR, and ASYP of preterm birth by sex, country, and year (from 1990 to 2021) from the GBD site. The male-to-female ratio was applied to quantify the gender difference in morbidity and disease burden. Absolute numbers, age-standardized rates per 100,000 population and percent of DALYs and YLLs of preterm birth attributable to particulate matter pollution, ambient particulate matter pollution, and household air pollution from solid fuels by sex, SDI, and territory were also obtained. Our study applied male-to-female ratio of DALYs, YLLs, ASDR, ASYR, and the difference in ASYP between males and females to quantify the gender variation. Statistical analyses in this study were conducted using R software (version 4.2.1) and Prism (version 9.5). The 95% Uncertainty Interval (95% UI) are given as the 2.5th and 97.5th percentiles of that distribution.

Results

Global trends in preterm birth rates and disease burden by sex

From 1990 to 2021, the global number of preterm births has shown a decreasing trend for both sexes, with a consistently higher burden observed in males. In 1990, the estimated number of preterm births was 13.45 million (95% UI: 13.58–13.32) for males and 9.55 million (95% UI: 9.66–9.43) for females. By 2021, these numbers had decreased to 12.33 million (95% UI: 12.46–12.19) and 9.22 million (95% UI: 9.33–9.11) (Table 1). Correspondingly, the male-to-female ratio of preterm birth counts had declined from 1.41 in 1990 to 1.34 in 2021 (Table 1), indicating a persistent but gradually narrowing sex disparity over time.

Table 1.

Absolute number per year and age-standardized rates of incidence and DALY per 100,000 population in 1990 and 2021 stratified by sex.

	Incidences, n (95% UI)			ASIR, n (95% UI)			DALYs, n (95% UI)			ASDR, n (95% UI)
	Male (million)	Female (million)	Male/female ratio	Male	Female	Male/female ratio	Male (million)	Female (million)	Male/female ratio	Male	Female	Male/female ratio
1990	13.45 (13.58–13.32)	9.55 (9.65–9.43)	1.41	405.15 (409.05–401.24)	309.26 (312.71–305.58)	1.31	71.10 (77.86–64.91)	53.24 (58.59–48.10)	1.34	2167.7 (2371.0–1979.6)	1741.8 (1916.2–1573.8)	1.24
2021	12.32 (12.46–12.19)	9.22 (9.33–9.11)	1.34	385.35 (389.59–381.09)	308.84 (312.37–305.13)	1.25	45.13 (53.29–38.48)	35.19 (40.30–30.06)	1.28	1368.9 (1624.6–1156.1)	1131.6 (1292.9–960.5)	1.21

DALY, disability-adjusted life year; ASIR, age-standardized rate of incidence; ASDR, age-standardized DALY rate.

After age-standardization, the ASIR for males in 1990 was 405.15 per 100,000 people, compared to 309.26 for females, with a male-to-female ratio of 1.31. By 2021, ASIRs had declined to 385.35 (95% UI: 389.59–381.09) for males and 308.84 (95% UI: 312.37–305.13) for females, with the ratio decreasing to 1.25 (Table 1). The ASIR for both sexes declined steadily from 1990 to 2016 but showed a mild rebound thereafter, reaching a secondary peak around 2016–2018 (Figure 1(a)). In contrast, the global disease burden attributable to preterm birth, measured by DALYs, showed a sustained decline from 1990 to 2021 (Figure 1(a)). Specifically, the DALYs for preterm male infants decreased from 71.10 million to 45.14 million, and those for female infants declined from 53.25 million to 35.20 million (Table 1). Correspondingly, the ASDR declined steadily in both sexes, with a more pronounced reduction in females, particularly after 2000, contributing to the narrowing of sex disparities in disease burden (Figure 1(b)).

Figure 1.

ASIR and ASDR of preterm birth by sex, 1990–2021. (a) ASIR of preterm birth by sex. (b) ASDR of preterm birth by sex. ASIR: age-standardized incidence rate; ASDR: age-standardized DALY rate; DALY: disability-adjusted life year.

Geographic variation in sex ratios of preterm birth burden in 2021

Subsequently, we analyzed national-level sex ratios of ASIR, ASDR, and ASYR in 2021. In 193 countries (94.6%), males had a higher ASIR, with the greatest predominance observed in Montenegro (1.78), Kyrgyz Republic (1.72), and South Africa (1.71) (Figure 2(a)). In contrast, 10 countries showed higher ASIRs in females, including Saint Lucia, Sao Tome and Principe, Djibouti, Somalia, Uruguay, Brunei, France, Czech Republic, Nigeria, and Argentina (Figure 2(a)). Among these, Brunei, France, and the Czech Republic are high-income countries. Notably, Romania was the only country with an equal ASIR between sexes (Supplemental Table 1).

Figure 2.

Sex ratio of ASIR, ASDR, and ASYR in 204 countries. (a) Male-to-female ratio of ASIR. (b) Male-to-female ratio of ASDR. (c) Male-to-female ratio of ASYR. DALY: disability-adjusted life year; YLL: years of life lost; ASIR: age-standardized incidence rate; ASDR: age-standardized DALY rate; ASYR: age-standardized YLL rate.

For the ASDR, 178 countries (87.3%) reported higher ASDRs in males, with the highest sex ratios in Mali (1.66), Namibia (1.58), and Ethiopia (1.55), all from sub-Saharan Africa (Figure 2(b)). Conversely, 23 countries had higher ASDRs in females, with the top six being Pacific Island nations: Cook Islands, Samoa, Tokelau, Guam, Niue, and Tonga (Figure 2(b)). Regarding ASYR, 184 countries (90.2%) exhibited higher ASYRs in males. The most extreme disparity was observed in the US Virgin Islands, where the male ASYR was 2.5 times that of females (Figure 2(c)). In most of these countries, the ASYR ratio exceeded the ASDR ratio. Interestingly, in Haiti, Iceland, and Laos, male ASYRs were higher than female ASYRs, despite lower male ASDRs (Supplemental Table 1), indicating that male infants may be more likely to die prematurely, whereas female infants may survive but experience more years lived with disability.

Preterm birth burden attributed to particulate matter pollution by sex, SDI, and region in 2021

Building on the observed sex disparities in preterm birth burden, we further examined how the burden associated with particulate matter pollution varied across sex, SDI levels, and 21 GBD regions in 2021. In 2021, particulate matter pollution contributed to 11.69 million YLLs and 11.70 million DALYs in males, approximately 1.3 times the values observed in females. Corresponding ASYR and ASDR in males were 365.4 (95% UI: 287.9–444.8) and 365.6 (95% UI: 288.3–445.1) per 100,000, respectively, both 1.24 times higher than female rates (Supplemental Table 2). In proportional terms, particulate matter pollution accounted for 31.1% (95% UI: 27.7–34.1) of ASYP and 26.7% (95% UI: 23.6–29.6) of ASDP in male, both higher than females (ASYP: 30.6%, ASDP: 26%) (Supplemental Table 2). Household air pollution accounted for 21.2 and 18.3% of ASYP and ASDP in males, compared to 20.7 and 17.6% in females, suggesting only minor sex differences (Supplemental Table 3). These findings indicate that males bear a higher absolute burden, while household air pollution may partly explain the subtle sex gaps observed in proportional metrics.

The burden attributable to air pollution increased as SDI decreases (Figure 3(a) and (b)). In 2021, low-SDI regions accounted for 8.82 million YLLs and 8.83 million DALYs. The ASYR and ASDR in these regions were both approximately 34 times higher than in high-SDI regions (Supplemental Table 2). Across all SDI strata, males consistently bore greater burdens, with sex ratios more pronounced for household air pollution (1.37) than for ambient particulate matter (1.30) (Supplemental Tables 3 and 4). In proportional terms, low-SDI regions again showed the heaviest burdens (ASYP: 34.2%, ASDP: 30.7%), compared to 6.9 and 4.4% in high-SDI regions (Figure 3(c) and (d)). Household air pollution followed a similar gradient, contributing 28.2% of YLLs in low-SDI regions but negligible shares in high-SDI settings (Supplemental Table 3). By contrast, the proportional burden attributable to ambient particulate matter was highest in middle-SDI regions (ASYP: 16.9%, ASDP: 13.8%), although absolute YLLs and DALYs peaked in low-middle SDI (≈2.8 million) (Supplemental Table 4).

Figure 3.

Sex disparities in disease burden of preterm birth attributable to particulate matter pollution by SDI quintile and GBD region. (a) ASYR attributable to household air pollution and ambient particulate matter pollution by SDI quintile and sex. (b) ASDR attributable to household and ambient air pollution by SDI quintile and sex. (c) ASYP attributable to household and ambient air pollution by SDI quintile and sex. (d) ASDP attributable to household and ambient air pollution by SDI quintile and sex. (e) ASYR attributable to household and ambient air pollution by GBD region and sex. (f) ASDR attributable to household and ambient particulate matter by GBD region and sex. ASDR: age-standardized DALY rate; ASYR: age-standardized YLL rate; ASYP: age-standardized YLL percent; SDI: socio-demographic index; ASDP: age-standardized DALY percent; GBD: Global Burden of Disease; DALY: disability-adjusted life year; YLL: years of life lost.

Marked regional heterogeneity was observed (Figure 3(e) and (f)). South Asia and Western sub-Saharan Africa experienced the highest burdens, accounting for 42 and 26% of global DALYs, respectively (Supplemental Table 2). In both regions, household air pollution was the dominant contributor, with ASYR values of 374.7 (95% UI: 260.9–508.6) for South Asia and 459.2 (95% UI: 342.9–575.9) for Western sub-Saharan Africa, and ASDR of 375.1 (95% UI: 261.2–509.0) for South Asia and 459.5 (95% UI: 343.0–576.2) for Western sub-Saharan Africa (Supplemental Table 3). In contrast, the high-income Asia-Pacific region had the lowest burden, with ASDR and ASYR values near 5.2, virtually unaffected by household air pollution (Supplemental Tables 2 and 3). Across all GBD regions, males exhibited a higher disease burden than females, though the magnitude varied. The male-to-female ratio (based on ASYR and ASDR) was highest in Eastern Europe for total particulate matter burden (1.49), in Australasia for household air pollution (1.6), and in Eastern sub-Saharan Africa for ambient particulate matter (1.5) (Supplemental Tables 2–4).

The proportion of preterm birth disease burden attributed to particulate matter pollution across different regions by sex

Across 21 GBD regions in 2021, household air pollution from solid fuels and ambient particulate matter pollution contributed substantially to the burden of preterm birth, as reflected in both ASYP and ASDP (Figure 4). For household air pollution, the highest burdens were observed in Eastern (33.3% (95% UI: 29.1–37.3)) sub-Saharan Africa (33.3% (95% UI: 29.1–37.3)) and Oceania (31.6% (95% UI: 22.7–42.8)) (Supplemental Table 3). By contrast, North Africa and the Middle East (15.4% (95% UI: 12.3–19.2)) and East Asia (16.3 (95% UI: 9.0–21.3)) showed the highest proportions of preterm birth attribute to ambient particulate matter pollution (Supplemental Table 4). In Australasia, high-income North America, high-income Asia-Pacific, and Western Europe, the contribution of household air pollution was negligible (ASDP and ASYP = 0) (Supplemental Table 3).

Figure 4.

ASYP and ASDP attributable to household and ambient air pollution in preterm birth by GBD region and sex (2021). (a) ASYP of preterm birth attributable to household and ambient air pollution by GBD region and sex. (b) ASDP of preterm birth attributable to household and ambient air pollution by GBD region and sex. DALY: disability-adjusted life year; YLL: years of life lost; ASYP: age-standardized YLL percent; ASDP: age-standardized DALY percent; GBD: Global Burden of Disease.

Sex-stratified analyses showed minor global differences in ASYP (0.5%) and ASDP (0.7%). These were mainly associated with household air pollution (0.6 and 0.7%), while ambient particulate matter had little impact (−0.1 and 0.0%). The largest sex differences were observed in Western sub-Saharan Africa, largely explained by household air pollution with ASYP (2.0%) and ASDP (2.3%) gaps between males and females (Supplemental Table 3).

Discussion

Based on the GBD 2021 database, this study sheds light on the persistent sex-based disparities in preterm birth rates and associated disease burden globally. Our analysis demonstrates that male infants consistently bear a higher burden of preterm birth compared to females, both in terms of incidence and long-term health outcomes. These findings are consistent with previous studies. For example, a study at Groote Schuur Hospital in South Africa reported a 1.12-fold higher preterm birth rate in males compared with females.⁸ Similarly, large-scale population data from Italy and Norway also demonstrated male predominance among preterm births.^29,30 The EPIPAGE study also reported a higher incidence of very preterm births among male infants.⁷

Based on our analysis of global data, the ASIR of preterm births peaked around 2016 and continued to rise in both sexes. A potential explanation for this increase is the implementation of China's two-child policy in 2016. This policy resulted in a significant rise in advanced maternal age (from 14.6 to 31.6%) and a doubling of multiple births.^31,32 Both factors are known to elevate the risk of preterm birth, and regional data indeed observed a rise in preterm birth rates following the policy implementation.^31,33 Given China's vast population, these demographic shifts are likely to have had a notable impact on global trends. Interestingly, this trend was not mirrored by a similar rise in the ASDR. Two factors may account for this discrepancy. First, advances in neonatal intensive care have markedly improved the survival of extremely preterm infants. According to the statistics, survival rates at 23 weeks’ gestation have increased from nearly 0 to 65% in some centers.³⁴ By 2014, over 98% of US neonatal intensive care units achieved mortality outcomes similar to the top-performing units from a decade earlier.³⁵ Second, the global fertility rates have steadily declined over the past few decades, particularly in high-income countries.³⁶ With fewer births overall, the absolute number of preterm-related deaths has remained relatively low, which may have attenuated the impact of increasing ASIR on ASDR.

Regarding the male-to-female birth ratio, we observed a decrease between 1990 and 2021. This trend aligns with shifts in birth sex ratios observed in several countries, including Japan,³⁷ the United States,³⁷ Finland,³⁸ and Denmark.³⁹ Furthermore, our findings further revealed that male infants bore a heavier disease burden than females, which is consistent with previous studies. For instance, a retrospective study from 1998 to 2004 in New South Wales and the Australian Capital Territory found that male infants exhibited higher mortality and an increased risk of adverse neurological outcomes.⁴⁰ Consistently, the United Kingdom Oscillation Study, involving 797 infants born at 23–28 weeks, showed that male infants were more likely to experience oxygen dependence, pulmonary hemorrhage, and neurodevelopmental abnormalities.¹⁰ Additionally, Hintz et al. confirmed a higher risk of neurodevelopmental impairment among extremely preterm and low birth weight male infants.¹¹

Our findings also revealed that in 2021, South Asia and sub-Saharan Africa carried the heaviest burden of preterm birth attributable to particulate matter pollution, with household air pollution having a more substantial impact than ambient sources. In sub-Saharan Africa, four out of every five children live in households reliant on unclean fuels.⁴¹ Higher PM_2.5 levels have been reported in families with young children in heavily contaminated areas of India.⁴² Indoor particulate matter levels in low- and middle-income countries were found to exceed WHO standards.⁴³ Moreover, the burden attributable to air pollution was more pronounced for YLLs than for DALYs, underscoring its disproportionate contribution to neonatal preterm mortality. Sex-specific analyses further demonstrated that male infants bore a higher disease burden from household air pollution than females, whereas sex-specific differences in the impact of ambient particulate matter pollution on preterm birth were negligible. This is consistent with previous research reporting that no significant interactions were found between sex and traffic-related air pollution in affecting epigenetic change.⁴⁴ Encouragingly, interventions, such as improved cookstoves and cleaner fuels, have been shown to significantly reduce indoor particulate matter levels, and may represent promising strategies to potentially mitigate the preterm birth burden in low-SDI regions.⁴³

Several limitations should be acknowledged in this study. Although the GBD 2021 incorporated methodological advances, including the newly developed BPRF to quantify heterogeneity, data quality for preterm birth remains sub-optimal in low-SDI regions, such as sub-Saharan Africa and South Asia.⁴⁵ In these settings, reporting often relies on aggregated hospital records rather than individual-level data, which may introduce inaccuracies and inconsistencies.⁴⁶ Moreover, gestational age is frequently estimated using the last menstrual period, a method vulnerable to recall bias and measurement error.^47,48 Such limitations hinder the accurate estimation of preterm birth prevalence and make it difficult to evaluate sex-specific disparities.⁴⁹ In addition, particulate matter pollution is the only quantifiable environmental risk factor currently included in the GBD framework, restricting the ability to assess other potentially relevant sex-specific exposures.

Conclusion

From 1990 to 2021, the preterm birth rate and disease burden appeared to be higher in male infants. Particulate matter pollution, particularly household air pollution, may have been associated with this disparity. Nevertheless, further research is required to better understand the potential role of air pollution in these outcomes.

Supplemental Material

sj-docx-1-sci-10.1177_00368504251387238 - Supplemental material for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021

Supplemental material, sj-docx-1-sci-10.1177_00368504251387238 for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021 by Ziming Zhang, Lingchen Li, Dandan Pan, Tieshuai Liu, Xinmin Ju, Qiqi Li, Mengting Hu, Tian Xie and Zheng Chen in Science Progress

Supplemental Material

sj-docx-2-sci-10.1177_00368504251387238 - Supplemental material for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021

Supplemental material, sj-docx-2-sci-10.1177_00368504251387238 for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021 by Ziming Zhang, Lingchen Li, Dandan Pan, Tieshuai Liu, Xinmin Ju, Qiqi Li, Mengting Hu, Tian Xie and Zheng Chen in Science Progress

Supplemental Material

sj-docx-3-sci-10.1177_00368504251387238 - Supplemental material for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021

Supplemental material, sj-docx-3-sci-10.1177_00368504251387238 for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021 by Ziming Zhang, Lingchen Li, Dandan Pan, Tieshuai Liu, Xinmin Ju, Qiqi Li, Mengting Hu, Tian Xie and Zheng Chen in Science Progress

Supplemental Material

sj-docx-4-sci-10.1177_00368504251387238 - Supplemental material for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021

Supplemental material, sj-docx-4-sci-10.1177_00368504251387238 for Sex differences in preterm birth and the impact of particulate matter pollution: A retrospective cross-sectional study of the Global Burden of Disease 2021 by Ziming Zhang, Lingchen Li, Dandan Pan, Tieshuai Liu, Xinmin Ju, Qiqi Li, Mengting Hu, Tian Xie and Zheng Chen in Science Progress

Footnotes

Acknowledgments

The authors would like to thank the collaborators of the Global Burden of Disease (GBD) Study 2021 for their work and all the individuals who contributed to the GBD 2021 for their extensive support in finding, cataloging, and analyzing data and facilitating communications. There is no scientific data generated or modified using AI.

ORCID iDs

Ziming Zhang

Tieshuai Liu

Zheng Chen

Ethical considerations

Not applicable. As this study used publicly available, de-identified data from the GBD 2021 database, ethical approval was not required.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Authors’ contributions

Conceptualization: ZC; data curation: DP and QL; formal analysis: ZZ and LL; funding acquisition: ZZ and DP; methodology: TL, XJ, and MH; software: MH; supervision: ZC; visualization: TX; writing—original draft: ZZ and LL; and writing—review and editing: all authors.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by grants from the National Natural Science Foundation of China (No. 82201890), Wu Jieping Medical Foundation Research Grant (No. 320.6750.2025-9-25), and Guiyang High-Level Innovative Young Health Talent Training Program Project (2019 Guiyang Health Bureau Technology Contract No. 17).

Data availability statement

The data for this study are available from Global Burden of Disease Study 2021 at . This public link to the database of GBD study is open, and the use of data does not require additional consent from IHME.

Supplemental material

Supplemental material for this article is available online.

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