IL1RL1 and hydrops fetalis: It was found that some inflammatory markers such as interleukin-33 (IL-33)/ST2 (suppressor of tumorigenicity 2; interleukin 1 receptor-like 1), IL-6, and tumor necrosis factor-alpha (TNF-α), were associated with HF, but they were not specific for HF and were often affected by other multiple comorbidities (Weinberg et al., 2002; Liu et al., 2014).