In-utero Hematopoietic Stem Cell Transplantation for the Treatment of Fetuses With Bart's Hydrops Fetalis Syndrome

Inclusion Criteria: * Pregnancy before 26 weeks and 0 day of gestational age with a diagnosis of BHFS confirmed by chorionic villus sampling, amniocentesis or cordocentesis; * The parents elected to pursue IUT and are willing to undergo subsequent IUT for the remainder of gestation. Exclusion Criteria: A) Fetal subjects: * Fetuses having a second major anatomic anomaly (not related to the underlying thalassemia) that contributes a significant morbidity or mortality risk; * Fetuses having a genetic or chromosomal abnormalities other than BHFS that contributes a significant morbidity or mortality risk; * Echocardiogram or ultrasound findings that indicate a high risk of fetal demise after fetal intervention; * Fetuses diagnosed with in-utero death prior to the actual intervention. B) Maternal subjects: * Maternal age \< 18 years, mentally handicapped or severely ill; * Maternal participants having one or more morbidities that would preclude bone marrow or peripheral blood stem cells harvest and fetal intervention including, but not limited to, bleeding disorder, maternal cardiac disease, maternal mirror syndrome, symptomatic maternal anemia, or if they develop preterm premature rupture of membranes or active preterm labor; * Unable to understand English or Chinese to give consent.