Numerous signals have been discovered in HF formation and growth, including transcription factors, growth factors, cytokines, neuropeptides, and hormones, such as SOX9 (sex-determining region Y-box 9), FGF7 (fibroblast growth factor 7), NFI (nuclear factor I), TRH (thyrotropin-releasing hormone), and corticosterone [6,7,8,9,10]. Here, TRH is linked to hydrops fetalis.