CD9 and hydrops fetalis: Expression of CD24, CD63, and CD81 were higher in OC patient exosomes than in HF exosomes, however, the statistically significant differences were revealed in the expression of CD24 on CD9-positive exosomes (Figure 1B, Table S1), both between HF plasma exosomes and OC patient plasma exosomes, and plasma exosomes and ascite exosomes of ill patients (p < 0.05).