GSTM1 and anemia (phenotype): Although there are some researches investigating the association of PM2.5 with Hb and anemia, most of them focus on the elderly, adults, and children (Elbarbary et al. 2020; Honda et al. 2017; Mehta et al. 2021; Morales-Ancajima et al. 2019; Wang et al. 2021), and few focus on pregnant women (Liao et al. 2019).