COL1A1 and hydrops fetalis: Based on the quantitative analysis of COL1A1-positive area in the whole slice prepared by Imge-Pro Plus, we found that the proportion of COL1A1-positive area in HF was much larger than normal control (13.61 ± 2.55% vs. 3.76 ± 0.64%, t-test p value = 1.1 × 10− 3, Fig. 7b).