Abstract: Objective：To examine association between the ambient air particulate matter pollution and the missed
abortion in which the embryo dies but miscarriage has not yet occurred during early pregnancy in Tianjin. Methods：A retrospective case-control study has been conducted with focus on the pertinent cases collected from 15 hospitals located in the urban core of Tianjin from January 2001 to December 2006. These cases experience missed abortions while controls undergo selective abortions. Each case is assigned one control matched with maternal age. Monthly average concentrations of ambient air particulate matter with aerodynamic diameters ≤10 μm（PM10） and total suspended particle （TSP） from 2001 to 2006 are obtained from the monitoring network of Tianjin Environment Monitoring Center. We assign air pollution exposures from the nearest monitoring station to each individuals-based residential home address by GIS model. Results：After adjusting for maternal age，gestational week，gravidity and parity. We found that relatively higher TSP（≥0.996 mg/m3）（OR=1.40，95%CI：1.06-1.86） exposure during peri-pregnancy period increased the risk of missed abortion. There is no correlation between PM10 exposure during progestation or conception and missed abortion. Conclusions：Exposed to relatively high levels of gaseous air particulate matter during peri-pregnancy period may be associated with missed abortion.

Key words: Abortion, missed, Air pollutionts, Particulate matter, Perinatology