Objective · To explore the pregestational and gestational risk factors associated with small for gestational age infant (SGA)different degrees. Methods · Mothers and single newborns delivered at Xinhua Hospital, Shanghai Jiao Tong University School of Medicine September 2013 to December 2016 were included. Multivariate Logistic regression was used to analyze the correlation between maternal pregnancy and pre-pregnancy risk factors and the occurrence of SGAdifferent degrees. Results · There were no statistically significant differences in maternal age, number of birth, education level, incidence of preterm birth and fetal sex in SGA. Maternal body mass index (BMI), gestational hypertension and accepting assisted reproduction were significantly correlated with SGA (all PConclusion · Maternal low BMI and hypertension are the risk factors of moderate SGA and accepting assisted reproduction are the risk factors of severe SGA, and the risk factors of SGAdifferent degrees are not the same.