GSTM1 and anemia (phenotype): In keeping with the UK and ACOG guidelines, the investigation of an etiology of anemia would be feasible if Hb levels were below 11.0 g/dL in the first and third trimesters and below 10.5 g/dL in the second trimester (ACOG), or below 11.0 g/dL in the first trimester and below 10.5 g/dL in subsequent trimesters (UK).