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ImportancePreterm birth (PTB) (gestational age <37 weeks) is a major cause of infant mortality and morbidity in the US and is marked by racial and ethnic and socioeconomic inequities. Further research is needed to elucidate the association of risk and protective factors with trends in PTB rates and with related inequities.ObjectiveTo describe the association of PTB rates with inequities as well as related risk and protective factors over the past decade in a US population–based cohort.Design, Setting, and ParticipantsThis retrospective cohort study of singleton live births in California from January 1, 2011, to December 31, 2022, was conducted using vital statistics records and hospital records. The cohort included births with a gestational age of 22 to 44 weeks.Main Outcomes and MeasuresPreterm birth rates by racial and ethnic group and by public and nonpublic insurance (considered as a proxy for socioeconomic status) were studied across years. Log-linear regression (relative risks with 95% CIs) was used to evaluate risk and protective factors within groups. Associations of PTB rates with risk and protective factors were assessed.ResultsThis study included 5 431 018 singleton live births to individuals who identified as American Indian or Alaska Native (0.3%), Asian (14.2%), Black (4.9%), Hispanic (47.8%), or White (27.0%). A total of 43.1% of births were to individuals with public health insurance. From 2011 to 2022, the overall PTB rate increased from 6.8% to 7.5% (change [SE], 10.6% [0.6%]; z score of 18.5; P < .001). Differences in PTB rates and associated changes were observed for racial and ethnic groups and insurance groups. For example, 2022 PTB rates ranged from 5.8% among White individuals with nonpublic insurance to 11.3% among Black individuals with public health insurance. From 2011 to 2022, PTB rates decreased from 9.1% to 8.8% (change [SE], −3.5% [4.2]; z score of −0.8; P = .42) among Black individuals with nonpublic insurance, whereas they increased from 6.4% to 9.5% (change [SE], 49.8% [16.0%]; z score of 3.1; P = .002) among American Indian or Alaska Native individuals with nonpublic insurance. Increases in some risk factors (eg, preexisting diabetes, sexually transmitted infections, mental health conditions) were observed in most groups, and decreases in some protective factors (eg, participation in the California Women, Infants, and Children program) (P for trend < .001 from 2011 to 2021) were observed mostly in low-income groups.Conclusions and RelevanceIn this cohort study of singleton live births in California, PTB rates increased in many groups. Persistent racial and ethnic and socioeconomic inequities were also observed. Changes in risk and protective factors provided clues to patterns of PTB. These data point to an urgent need to address factors associated with PTB at both the individual and population levels.
ImportancePreterm birth (PTB) (gestational age <37 weeks) is a major cause of infant mortality and morbidity in the US and is marked by racial and ethnic and socioeconomic inequities. Further research is needed to elucidate the association of risk and protective factors with trends in PTB rates and with related inequities.ObjectiveTo describe the association of PTB rates with inequities as well as related risk and protective factors over the past decade in a US population–based cohort.Design, Setting, and ParticipantsThis retrospective cohort study of singleton live births in California from January 1, 2011, to December 31, 2022, was conducted using vital statistics records and hospital records. The cohort included births with a gestational age of 22 to 44 weeks.Main Outcomes and MeasuresPreterm birth rates by racial and ethnic group and by public and nonpublic insurance (considered as a proxy for socioeconomic status) were studied across years. Log-linear regression (relative risks with 95% CIs) was used to evaluate risk and protective factors within groups. Associations of PTB rates with risk and protective factors were assessed.ResultsThis study included 5 431 018 singleton live births to individuals who identified as American Indian or Alaska Native (0.3%), Asian (14.2%), Black (4.9%), Hispanic (47.8%), or White (27.0%). A total of 43.1% of births were to individuals with public health insurance. From 2011 to 2022, the overall PTB rate increased from 6.8% to 7.5% (change [SE], 10.6% [0.6%]; z score of 18.5; P < .001). Differences in PTB rates and associated changes were observed for racial and ethnic groups and insurance groups. For example, 2022 PTB rates ranged from 5.8% among White individuals with nonpublic insurance to 11.3% among Black individuals with public health insurance. From 2011 to 2022, PTB rates decreased from 9.1% to 8.8% (change [SE], −3.5% [4.2]; z score of −0.8; P = .42) among Black individuals with nonpublic insurance, whereas they increased from 6.4% to 9.5% (change [SE], 49.8% [16.0%]; z score of 3.1; P = .002) among American Indian or Alaska Native individuals with nonpublic insurance. Increases in some risk factors (eg, preexisting diabetes, sexually transmitted infections, mental health conditions) were observed in most groups, and decreases in some protective factors (eg, participation in the California Women, Infants, and Children program) (P for trend < .001 from 2011 to 2021) were observed mostly in low-income groups.Conclusions and RelevanceIn this cohort study of singleton live births in California, PTB rates increased in many groups. Persistent racial and ethnic and socioeconomic inequities were also observed. Changes in risk and protective factors provided clues to patterns of PTB. These data point to an urgent need to address factors associated with PTB at both the individual and population levels.
IntroductionPrevious systematic reviews investigating the effects of green and blue space (GBS) on maternal and neonatal health have mainly focused on cross-sectional evidence, limiting potential causal inferences. The last review on the topic was published in January 2024. This review focused on residential greenness effects and neonatal health only but did not include other green/blue space measures, or maternal health outcomes. This review also only included papers published up to June 2023; discounting the 15 studies that have been published since. Thus, this study will capture the growing number of studies that generate causal evidence and aims to investigate the association between GBS and maternal and/or neonatal health.Methods and analysisThe study protocol was developed with reference to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. This review will include study designs such as experiments, quasi-experiments, longitudinal studies and more. The study independent variable must be a GBS, green space and/or blue space measure. Eligible maternal health outcomes are those reported during pregnancy and up to 1 year after pregnancy. Neonatal health outcomes are limited to neonates no older than 28 days. A total of seven online databases will be searched: Medline, Scopus, Web of Science, PsycInfo, Embase, Environment Complete, and Maternity and Infant Care Database. Abstract and full-text screenings will be undertaken by three reviewers. Risk of bias assessment will be conducted based on the Risk of Bias in Non-randomized Studies-of Exposure framework.A narrative synthesis will be undertaken. If sufficiently comparable studies are identified, meta-analyses using random effects models will be conducted. We will explore heterogeneity using the I2test.Ethics and disseminationEthical approval is not required as all the data will be derived from published primary studies that have already obtained ethical permissions. The findings will be disseminated through relevant conferences and peer-reviewed publications.PROSPERO registration numberCRD42023396372.
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