SOSTDC1 and hydrops fetalis: In cluster 4, we found that genes were enriched in epithelial cell differentiation (FZD1 and BMP7), HF morphogenesis (KRT71, WNT10A, KRT27, KRT25 and SOSTDC1) and sebaceous gland development (WNT10A and ZDHHC21), and their expression levels peaked in the G2 period.