GSTM1 and nutritional disorder: • Daily iron supplementation (effects in the 3rdtrimester and delivery): ○ increased the mean maternal Hb concentration by 4.59 g/L (95%CI: 3.72–5.46) compared with the control group; ○ significantly reduced the risk of anemia (RR 0.50; 95%CI: 0.42–0.59); ○ significantly reduced iron deficiency (RR 0.59, 95%CI: 0.46–0.79) and ferropenic anemia (RR 0.40, 95%CI: 0.26–0.60).• The effects on Hb concentration in the 2ndtrimester were not evaluated by a small number of trials.