FGF21 and hydrops fetalis: The lower level of mitokines, such as FGF21 and GDF15, in HF participants, combined with the evidence for better mitochondrial function we reported previously in this HF group (Ubaida‐Mohien et al. 2022) is consistent with the evidence that FGF21 and GDF15 reflect mitochondrial stress (Ito et al. 2018; Lehtonen et al. 2016).