本文基于我国20世纪90年代具有代表性的中国农村出生数据，探究了孕期PM2.5暴露对出生结果的影响。因为1991年至2000年间，中国农村的人口迁移能力有限，且人们还没有意识到PM2.5的危害，并不采取防护措施，这就使本文在很大程度上能够解决样本选择与内生性问题。通过对出生体重、低出生体重指标和巨大儿指标的分析，本文发现孕期PM2.5浓度对新生儿的出生体重以及出现低出生体重的概率没有显著影响，但在孕中期阶段会显著影响新生儿出现巨大儿的概率，且该影响对于不同性别的新生儿具有异质性。孕期PM2.5并不是通过导致过期产或孕期生长过盛进而导致巨大儿的发生，其具体的作用机制还需要更多生物学探索。

This paper probes into the effects of prenatal exposure to PM2.5 on birth outcomes using a nationally representative dataset on 1990s rural China. From 1991 to 2000, the ability of population migration in rural China was limited, and people did not realize the harm of PM2.5 and did not take protective measures, which enabled this paper to address the endemic identification challenges and endogeneity to a large extent. Through the analysis of birth weight, low birth weight and macrosomia, we find that PM2.5 exposure had no significant effect on infant birth weight and the incidence of low birth weight, but significantly affected the incidence of macrosomia in the second trimester, and this effect is heterogeneous for infants of different sexes. Prenatal exposure to PM2.5 does not lead to macrosomia by causing delayed delivery or overgrowth during pregnancy. Its specific mechanism still needs more biological exploration.