Abstract: Objective　To explore the perinatal risk factors of early onset thrombocytopenia (EOT) in full-term small for gestational age infants. Methods　A 1:1 or 1:2 matched case control study was carried out. A total of 93 full-term small for gestational age infants with EOT were selected from April 2008 to July 2014 as the case group, and the non EOT full-term small for gestational age infants with the birth weight difference <250 g and the gestational age difference <3 days were selected as the control group. The clinical data during perinatal period and laboratory examination results after admission were collected retrospectively. And the differences between the two groups were compared. Results　The incidence of intrauterine distress (41.9% vs. 25.8%, χ2=7.35, P=0.007), amniotic fluid contamination (39.8% vs. 27%, χ2=4.66, P=0.031), and early-onset sepsis (39.8% vs. 27%, χ2=4.66, P=0.031) were significantly higher in the case group than those in the control group. Conditional logistics regression analysis showed that intrauterine distress (β=0.60, OR=1.82, 95%CI=1.04~3.17, P=0.035) and early-onset sepsis (β=1.69, OR=5.44, 95%CI=1.11~26.76, P=0.037) were related to EOT. Conclusions　Intrauterine distress and early-onset sepsis are risk factors for the onset of EOT in full-term small for gestational age infants.