GSTM1 and hydrops fetalis: Meta-analysis of the two RCTs involving HF patients (Serrano-Trenas et al. 2011; Bernabeu-Wittel et al. 2016) showed no evidence of a difference in Hb concentration at ‘short-term’ follow-up (MD − 0.32 g/L, 95% CI − 3.28 to 2.64, p = 0.21, I2 = 37%) (Fig. 3).