Background:Mild hypoxic-ischemic encephalopathy (HIE) injury is becoming the major type in neonatal brain diseases.The aim of this study was to assess brain maturation in mild HIE neonatal brains using total maturation score (TMS) based on conventional magnetic resonance imaging (MRI).Methods:Totally,45 neonates with clinically mild HIE and 45 matched control neonates were enrolled.Gestated age,birth weight,age after birth and postmenstrual age at magnetic resonance (MR) scan were homogenous in the two groups.According to MR findings,mild HIE neonates were divided into three subgroups:Patt Ⅰ,neonates with normal MR appearance; Patt Ⅱ,preterm neonates with abnormal MR appearance; Patt Ⅲ,full-term neonates with abnormal MR appearance.TMS and its parameters,progressive myelination (M),cortical infolding (C),involution of germinal matrix tissue (G),and glial cell migration bands (B),were employed to assess brain maturation and compare difference between HIE and control groups.Results:The mean of TMS was significantly lower in mild HIE group than it in the control group (mean ± standard deviation [SD] 11.62 ± 1.53 vs.12.36 ± 1.26,P ＜ 0.001).In four parameters of TMS scores,the M and C scores were significantly lower in mild HIE group.Of the three patts of mild HIE,Patt Ⅰ (10 cases) showed no significant difference of TMS compared with control neonates,while Patt Ⅱ (22 cases),Ⅲ (13 cases) all had significantly decreased TMS than control neonates (mean ± SD 10.56 ± 0.93 vs.11.48 ± 0.55,P ＜ 0.05; 12.59 ± 1.28 vs.13.25 ± 1.29,P ＜ 0.05).It was M,C,and GM scores that significantly decreased in Patt Ⅱ,while for Patt Ⅲ,only C score significantly decreased.Conclusions:The TMS system,based on conventional MRI,is an effective method to detect delayed brain maturation in clinically mild HIE.The conventional MRI can reveal the different retardations in subtle structures and development processes among the different patts of mild HIE.