GSTM1 and gestational diabetes: Pooled analysis showed that women with GDM had significantly higher Hb levels (0.343 [95% CI 0.134–0.553] p = 0.01, sensitivity analysis: 0.174 [95% CI 0.0343–0.315] p = 0.01) and RBC (0.387 [95% CI 0.224–0.550] p < 0.001) compared with the control group.