The association between maternal exposure to PM_2.5 and birthweight varies geographically, which may be caused by susceptibility. Whether this population-level association is a function of mixtures of individuals with different susceptibilities is unclear. We investigated the probability distribution of individuals with different susceptibilities to PM_2.5-related birthweight change, and evaluated spatial variation of the effect across the United States (US). We estimated the individual-level susceptibility using the effect of PM_2.5 among a homogenous subpopulation, which was defined by a specific combination of modifiers. According to frequencies for all combinations, we derived the probability distribution of differential susceptibilities across the US and by states. From birth certificates across the US (1999–2004), we analyzed a total of 18,317,707 samples of singletons. Of the samples, 54–55% were assigned valid exposures, and linked to PM_2.5. The subpopulation-specific associations of PM_2.5 on birthweight change (i.e., susceptibilities) ranged from negative to positive. For the first-trimester exposure, 61.4% of the associations were negative, and the mean was −1.01 g (95% confidence interval, CI: −1.63, −0.38) of birthweight change per 5 μg/m³ increase of PM_2.5. The state-level associations varied (from −2.04 g [−2.76, −1.31] in New Hampshire to −0.30 g [−1.01, 0.41] in Texas) with demographic compositions in the US. The between-state variations of maternal race and education level were the greatest contributors to the spatial heterogeneity. Our findings may be useful to the policymaker in planning interventions for subpopulations susceptible to ambient pollution.

孕产妇暴露于PM _2.5与出生体重之间的关联在地理上有所不同，这可能是由于易感性引起的。尚不清楚这种人群水平的关联是否是具有不同易感性的个体的混合的功能。我们调查了对PM _2.5相关的出生体重变化有不同敏感性的个体的概率分布，并评估了整个美国（US）的影响的空间变化。我们使用PM _2.5的影响估计了个人水平的易感性在同一个亚群中，这是由修饰符的特定组合定义的。根据所有组合的频率，我们得出了美国和各州差异磁化率的概率分布。根据全美（1999-2004）的出生证明，我们分析了总计18,317,707个单身人士样本。在样本中，有54–55％的样本被指定为有效暴露量，并与PM _2.5相关联。PM _2.5与出生体重变化（即易感性）的亚人群特异性关联从负到正。对于孕早期，每5μg/ m ³出生体重变化的关联为61.4％为阴性，平均值为-1.01 g（95％置信区间，CI：-1.63，-0.38）增加PM _2.5。各州间的关联因美国的人口组成而异（从新罕布什尔州的-2.04 g [-2.76，-1.31]到德克萨斯州的-0.30 g [-1.01，0.41]）。孕产妇种族和教育水平的州际差异是造成空间异质性的最大原因。我们的发现对于政策制定者制定针对易受环境污染影响的亚人群的干预措施时可能有用。