To date, there are numerous systematic reviews and meta-analyses of prospective cohorts that relate maternal anaemia during the first trimester of pregnancy with increased risks for certain adverse pregnancy outcomes [16,23], but evidence related to high Hb concentrations is more limited [14,15,17,24], and none of them analysed their effect on the risk of miscarriages. The gene discussed is GSTM1; the disease is anemia (phenotype).