- enrolled in conflicting clinical trials (such as a randomized controlled blinded trial of another pulmonary vasodilator therapy); Note: mothers enrolled in fetal tracheal occlusion studies such as FETO may be enrolled if permitted by investigators of the fetal tracheal occlusion study; [FETO refers to fetoscopic endoluminal tracheal occlusion and involves occlusion of fetal trachea with a balloon device at mid-gestation and subsequent removal in later gestation]