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Introduction: Improvements in obstetric/neonatal care have increased the survival rates of extremely-preterm-born (EP), though followed by an increased number, and degrees, of white matter injury (WMI), and long-lasting neurodevelopmental impairments. Study aim: to investigate consequences of EP birth on the evolving white matter microstructure and myelination; and its causative role on acquired IQ and sensory-motor functions.

Participants and methods: Two MRI methods (3T; DTI and SyMRI) used to calculate white matter properties and associations with IQ and sensory-motor functions in children born FT and EP at 12-y. In total N = 57 children; 32 FT (GA 38-42), and 25 EP (GA 22- <27) successfully performed MRI and administered WISC-V and Beery visual-motor integration (VMI) test. DTI used for analyzing fractional anisotropy (FA), mean diffusivity (MD), axial- (AD) and radial diffusivity (RD). SyMRI (T1-T2-R1-R2 and PD) for analyzing myelin segmentation, white-matter (WM), gray-matter (GM), cerebrospinal fluid (CSF), and brain parenchyma volume (BPV).

Results: Children born EP had significant smaller total brain (BPV), less GM, WM and more CSF/ICV compared to FT born. GA correlated positively with brain volumes, myelin, and with IQ and Beery-WMI. For EPs myelin correlated positively with GA, WISC-V and Beery-VMI. EPs had significant higher RD and AD compared to FT, no significant FA difference found. Within EP-group, myelin content correlated positively with FA and negatively with RD and AD.

Conclusion: These findings suggest that EP births is associated with high-risk for long-lasting, globally compromised white matter myelination and microstructural organization which causes adverse cognitive and sensory-motor functions.