PTGER4 and hydrops fetalis: Other studies also localised key prostanoid receptors in the HF, especially within the dermal papilla, including FP, prostaglandin E2 receptors (EP2, EP3, EP4), prostaglandin D2 receptor (DP2), prostanoid thromboxane A2 receptor (TP), and prostaglandin I2 receptor (IP) (Khidhir et al., 2013a; Colombe et al., 2008; Xu and Chen, 2018).