For example, HOXC13, DBI, FZD3, ZDHHC21, KRT8, and SMAD4. Several signaling pathways related to HF development, including the Rap1, Ras, MAPK, Jak–STAT, and PI3K-Akt pathways, were identified across the 3 HF development stages. Here, SMAD4 is linked to hydrops fetalis.