Objective: To examine the association between exercise during pregnancy and preterm birth (PTB). Design: Retrospective cohort analysis. Setting: Jinan, China. Population: Singleton live births from December 2018 to December 2019. Methods: Questionnaires contained items about physical exercise (frequency, time, and primary exercise patterns) during pregnancy and each trimester. Adjusted odds ratios (OR) were estimated using logistic regression. Variable selection for the multivariate models was guided by the directed acyclic graph. The median effect was analyzed by the sequential test. Main Outcome Measures: PTB. Results: The prevalence of PTB in this study was 4.38% (285/6501). The adjusted OR (95% CI) for the risk of PTB related to exercise during pregnancy was 0.74 (0.58-0.95). During the 1st and 2nd trimesters, the ORs (95% CI) for 2.5 to 7 hours of exercise per week were 0.77 (0.59-0.99) and 0.74 (0.57-0.96). During the 3rd trimester, the ORs (95% CI) for 2.5 to 7 hours and more than 7 hours of exercise per week were 0.74 (0.56-0.96) and 0.65 (0.44-0.94). After stratifying the subjects, the association was only found among subjects without pregnancy complications. Pregnancy complications partially mediated (52.40%) the relationship between exercise during pregnancy and PTB. Conclusions: Exercise during pregnancy was a protective factor of PTB for women without pregnancy complications. 2.5 to 7 hours of exercise (like walking) per week may be appropriate in three trimesters of pregnancy, and the time could be extended in the 3rd trimester. Keywords: Preterm birth; Exercise; Pregnancy; Trimester; Mediation analysis

Background: The incidence of eczema is higher in children aged 0-2 years, but the long-term effect of air pollutants exposure in early life on the risk of eczema development is unclear. Methods: We conducted a birth cohort study in Jinan, China, to explore the effect of early life air pollutant exposure on the risk of eczema in younger children. An inverse distance weighting method was used for individual exposure assessment. Binary and multivariate logistic models were used to investigate the effects of air pollutants on eczema, the distributed lag model to find sensitive windows of exposure, weighted quantile sum model and principal component analysis to explore the combined effects of multiple pollutants. Results: The cumulative incidence rate for eczema among 5819 children aged 2 was 19.8%. Exposure to high levels of O 3 during pregnancy ( OR 1.12, 95% CI 1.06-1.19) and during the first year after birth ( OR 1.24, 95% CI 1.03-1.50) increased the risk of eczema. PM 2.5-10 during pregnancy ( OR 1.31, 95% CI 1.20-1.43), PM 2.5 ( OR 1.08, 95% CI 1.01-1.15) and PM 2.5-10 ( OR 1.07, 95% CI 1.00-1.14) during the first year after birth also increased the risk of eczema. The critical window for O 3 and PM exposure was the third trimester and early postnatal period. Moreover, in the combined effect of multiple pollutants, O 3 played a dominant role during pregnancy (weighting > 0.3), with a predominantly O 3 principal component associated with eczema risk (adjusted OR 1.011, 95% CI 1.007-1.015). Conclusions: Exposure to air pollutants O 3 and PM in early life increased the risk of eczema at 0-2 years of age, and the sensitivity window appeared earlier. O 3 exposure during pregnancy played a key role in the combined effect of pollutants on eczema risk.