Abstract: Objective To determine the risk factors of birth weight ≥2 500 g infants small than gestational age (SGA) and the common adverse perinatal outcome. Methods A total of 183 infants with birth weight (≥2 500 g) less than gestational age in the Department of Obstetrics of our hospital from January 1, 2013 to April 8, 2018 were selected as the case group. Another 183 cases of appropriate for gestational age (AGA) infants with birth weight ≥2 500 g were selected as the control group. The related indexes affecting neonatal birth weight were compared between two groups, including maternal factors [maternal body mass index (BMI), pregnancy complications], fetal factors (sex, parity), placental and umbilical cord factors. The clinical data of fetal distress, amniotic fluid loss and neonatal diseases were analyzed by SPSS software version 19.0. Results The maternal BMI was less in case group than that of control group, while umbilical cord placenta abnormalities, the ratios of female infants and the first birth were higher in case group than those of the control group (P＜ 0.05). Logistic regression analysis showed that abnormal placenta and umbilical cord, female infants and first fetus were the main risk factors for SGA (≥ 2 500 g), and higher maternal BMI was the protective factor of SGA (≥2 500 g). The incidence of oligohydramnios, fetal distress and birth defects in SGA during perinatal period were significantly higher than those in AGA(≥ 2 500 g, P＜0.05). Conclusion The risk factors and perinatal outcomes for infants (≥2 500 g SGA) have particularity. It is expected that high-risk factors can be closely monitored by strengthening screening and guidance during pregnancy and perinatal period to reduce the occurrence and improve prognosis.

Key words: infant, low birth weight, small for gestational age infant, appropriate for gestational age infant, risk factors, adverse perinatal outcome