Background Fine particulate matter (PM2.5) is not an established, but a strongly suspected risk factor in the occurrence of adverse maternal and foetus outcomes. Currently, the researchers have an interest in the critical time window for maternal exposure to PM2.5, and maternal and foetus health. Although exposure to PM2.5 is likely to have adverse effects from the early pregnancy, including the period of implantation, there is not enough evidence. To evaluate the effects of PM2.5 exposure and its components in the early pregnancy, we used abnormal cord insertion, which is one of placental implantation abnormalities, as an outcome, and examined the PM2.5-cord insertion association.
Methods Data on 83,454 mothers who delivered singleton births at 39 cooperating hospitals between 2013 and 2015 in 23 Tokyo wards was obtained from the Japan Perinatal Registry Network database, which was managed by the Japan Society of Obstetrics and Gynaecology. At one central monitoring site, fine particle was collected on a filter each day, and carbon and ion components of PM2.5 were analysed. The period of the first trimester (0–13 gestational weeks) was estimated to each woman, and the average concentrations in that period were calculated by the daily measurement of PM2.5 and its components. Abnormal cord insertion was defined as velamentous and marginal cord insertion. The odds ratios (ORs) of abnormal cord insertion were estimated using multi-level logistic regression analysis.
Results In this population, the mean age at delivery was 33.7 years, and the proportion of abnormal cord insertion accounted for 4.5%. The median concentration of total PM2.5 over the first trimester was 16.1 (interquartile range (IQR) = 3.6) μg/m3. Exposure to total PM2.5 was associated with abnormal cord insertion (OR per IQR = 1.09, 95% CI = 1.02–1.16). In the multi-component model, organic carbon was only component that increased the odds of abnormal cord insertion in a consistent manner. In addition, exposure to organic carbon over the first month of pregnancy (implantation period) was clearly associated with outcome.
Conclusion The findings in this study supported our hypothesis that exposure to PM2.5 has unfavourable effects from the early pregnancy.
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