IGF1 and hydrops fetalis: When analyzing the subgroups based on age difference, we found that IGF-1 levels were significantly associated with HF in the subgroup of “age difference ≥5 years” [SMD = −0.73, 95% CI (−1.42, −0.04), P = 0.038; I2 = 96.5%], but not in the subgroup of “age difference < 5 years” (Figure 3A).