摘要Background Small for gestational age (SGA) infants are associated with a high rate of oligohydramnios, stillbirth and cesarean delivery. Among SGA patients there is a higher risk of neonatal complications, such as polycythemia, hyperbilirubinemia, and hypothermia. Additionally, the SGA infant is prone to suffer from major neurologic sequelae, as well as cardiovascular system disease, in later life. Proper monitoring and therapy during pregnancy are, therefore, of utmost importance. The present study aimed to investigate the influential and prognostic factors of SGA infants.Methods From January 2001 to June 2007, a total of 55 SGA neonatal infants were included in a study group. All were born at Peking Union Medical College Hospital, with regular formal antenatal examinations. In addition, a total of 122 cases of appropriate for gestational age (AGA) infants were bom at the same time and were registered into a control group. All cases were singleton pregnancies with detailed information of the maternal age, gravidity, parity, maternal height and weight, complications, uterine height and abdominal circumference, results from transabdominal ultrasonography between 32-38 gestational weeks, pregnancy duration, delivery manner, placenta, umbilical cord, and neonatal complications.Results Significant differences were observed in placenta weight and neonatal malformations between the study and control groups. Multivariate analysis revealed increased parity, maternal hyperthyroidism and hyperthyroidism history as risk factors. Fetal abdominal circumferences less than 30 and 32 cm at 32-38 gestational weeks respectively, as determined by ultrasonography, resulted in a Youden index of 0.62.Conclusions SGA infants were associated with a greater risk of smaller placentas and infant malformations. Increased parity, maternal hyperthyroidism, and a hyperthyroid history were risk factors for SGA infants. Fetal abdominal circumference less than 30 cm at 32 gestational weeks and less than 32 cm at 38 weeks, as determined by ultrasonography, was considered an effective index for SGA.