GSTM1 and anemia (phenotype): Our null findings on maternal preconception Hb concentration and birth outcomes contrast with earlier findings in a systematic review where preconception anemia was associated with an increased risk of low birthweight (OR 1.72; 95% CI: 1.31–2.26) and SGA births (OR 1.79; 95% CI: 1.39–2.31) [5].