Abstract： This cross-sectional study recruited consecutively 347 patients (178 males,169 females) aged 19 to 30 years with a diagnosis of MDD according to Diagnostic and Statistical Manual of Mental Disorders,Fifth Edition (DSM-V) criteria who underwent in-person interviews,the mini international neuropsychiatric interview,and physical examinations by experienced psychiatrists at Division of Neuropsychiatry,Department of Neurology,Xuanwu Hospital of Capital Medical University (Beijing,China) between August 20,2015,and December 28,2018.All patients were excluded with anemia,thyroid dysfunction,mental retardation,neurologic conditions,bipolar disorders,schizophrenia,and other mental disorders.Depressive symptoms were assessed with the Hamilton rating scale for depression (HAMD-17) by three experienced psychological testing technicians who were blinded to all subjects' birth delivery types at the Neuropsychological Center of Department of Neurology of Xuanwu Hospital.The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Xuanwu Hospital.As a retrospective study and data analysis were performed anonymously,this study was exempt from the informed consent from patients.