Exposure to air pollutants during the early weeks of pregnancy, and placenta praevia and placenta accreta in the western part of Japan

Background: Placenta praevia is an obstetric complication involving placental implantation in the lower uterine segment. Given the suggested aetiology of placenta praevia, adverse biological effects of air pollutants, such as plasma viscosity increment, endothelial dysfunction, and systemic inflammation, have the potential to induce low implantation. We explored the association between exposure to air pollutants during the pregnancy period up to implantation, and placenta praevia, in pregnant Japanese women. The outcome also included placenta accreta, which often exists in combination with placenta praevia. Methods: From the Japan Perinatal Registry Network database, we obtained data on 40,573 singleton pregnant women in western Japan (Kyushu-Okinawa Districts) between 2005 and 2010. We assigned pollutant concentrations (suspended particulate matter [SPM], ozone, nitrogen dioxide [NO₂], and sulphur dioxide [SO₂]), measured at the nearest monitoring station to the respective delivery hospital of each woman. A logistic regression model was used to adjust for several covariates. Results: The odds ratios (ORs) of placenta praevia per 10 units increase were 1.12 (95% confidence interval (CI) = 1.01-1.23) for SPM over 0-4 weeks of gestation, and 1.08 (1.00-1.16) for ozone. The association between exposure to NO₂ and SO₂, and praevia, was in the direction of increased risk. SPM exposure during 0-4 weeks was associated with placenta accreta without praevia (OR = 1.33, 95% CI = 1.07-1.66). We found no association with exposure to air pollutants during 5-12 weeks and the second trimester. Conclusions: Exposure to air pollutants through to implantation was positively associated with placenta praevia and accreta.