GSTM1 and anemia: Longitudinal association over pregnancy from 18 to 35 weeks’ gestation of anaemia (Hb < 10.5 g/dL), iron deficiency (Fer < 15 μg/L) and iron deficiency erythropoiesis (sTfR > 8.3 mg/L) with a) coughing, b) diarrhoea, c) fever, d) nausea, e) vomiting, f) headache and g) extreme tiredness (n = 184).