YTHDF2 and hydrops fetalis: To further explore the underlying mechanism of YTHDF2 upregulation during HF progression, we firstly examined the interaction between RNA polymerase II, which is mainly responsible for transcriptional initiation of gene [22], and Ythdf2 gene promoter regions [range from 0 to −2000 bp from transcription start site, including region-1 (0 to − 1000 bp) and region-2 (− 1001 bp to 2000 bp)].