EDN1 and persistent fetal circulation syndrome: In the cohort of neonates tested for ET-1, there were no significant differences in the baseline characteristics between the sequenced PPHN and non-PPHN infants; ET-1 levels were 2.794 ± 2.634 pg/mL and 2.202 ± 1.731 pg/mL, respectively (P = 0.722).