Effect of Autologous Cord Blood-mononuclear Cells Infusion on Immune Microenvironment in Infants Born Very Preterm in NICU

Inclusion criteria 1. born at study hospitals; 2. monozygotic twins (confirmed by ultrasonographic diagnosis before birth and confirm again with obstetricians during and after delivery, as monochorionic diamniotic twins and monochorionic monoamniotic Twins twins were both monozygotic twins, therefore they will be both eligible); 3. gestational age (GA) \<32 weeks (GA was calculated based on the date of the last menstrual period of the mother and an ultrasonographic screening performed during the first trimester of pregnancy); 4. enrolled within the first 24 postnatal hours; 5. free of severe perinatal asphyxia (defined as an Apgar score of 0-3 for more than 5 minutes, a cord blood gas pH \<7.00, or both); 6. free of severe congenital anomalies or genetic syndromes; 7. free of maternal sepsis24,25; 8. Written informed consent is obtained from the parents or guardians of the infants; 9. Either of the twins has available umbilical cord blood (UCB) , and the cell number was no more than 10×107 cells per kilogram, but should not be less than 2×107 cells per kilogram. Exclusion criteria (1) they exhibit severe congenital abnormalities (detected via prenatal ultrasound); (2) expected to die within the first 24 hours; (3) diagnosed with severe twin-to-twin transfusion syndrome confirmed by prenatal ultrasonography24.