Exposure to Ambient Particulate Matter during Specific Gestational Periods Produces Adverse Obstetric Consequences in Mice

BACKGROUND: Epidemiological studies associate inhalation of fine-sized particulate matter (PM2.5) during pregnancy with preterm birth (PTB) and low birth weight (LBW) hut disagree over which time frames are most sensitive, or if effects are cumulative. OBJECTIVES: Our objective was to provide experimental plausibility for epidemiological observations by testing the hypothesis that exposure to PM2.5 during discrete periods of pregnancy results in PTB and LBW. METHODS: For the first study, timed-pregnant B6C3F(1) mice were exposed to concentrated ambient PM2.5 (CAPs) or filtered air (FA) throughout pregnancy [6 h/d from gestational day (GD) 0.5 through GD16.5]. A follow-up study examined the effects of CAPs exposure during discrete gestational periods (1: GD0.5-5.5; 2: GD6.5-14.5; 3: GD14.5-16.5; 4: GD0.5-16.5) aligning to milestones during human development. RESULTS: In the first experiment, exposure to 160 [mu gCAPs/m(3) throughout pregnancy decreased gestational term by 0.5 d (similar to 1.1 wk decrease for humans) and birth weight by 11.4% compared with FA. The follow-up experiment investigated timing of CAPs exposure (mean concentrations at 178, 193, 171, and 173 mu g/m(3) for periods 1-4, respectively). Pregnancy was significantly shortened (vs. FA) by similar to 0.4d when exposure occurred during gestational periods 2 and 4, and by similar to 0.5d if exposure occurred during period 3. Exposure during periods 1, 2, and 4 reduced birth weight by similar to 10% compared with FA, and placental weight was reduced (similar to 8%) on GD17.5 if exposure occurred only during period 3. CONCLUSIONS: Adverse PM2.5-induced outcomes such as PTB and LBW are dependent upon the periods of maternal exposure. The results of these experimental studies could contribute significantly to air pollution policy decisions in the future.