Persistent antithrombin III deficiency: risk factor for thromboembolic complications in neonates small for gestational age.

Coagulation and fibrinolytic factors were investigated daily in 24 SGA and 26 AGA neonates. The results were correlated with placental form and structure and with hematologic values. In the SGA infants, a higher incidence of placental infarction (P less than 0.01), polycythemia (P less than 0.005), and thrombocytopenia (P less than 0.001) was present. During the first 9 days, the mean antithrombin III level in the AGA group increased from 0.36 to 0.53 U/ml, whereas in SGA neonates this value was initially significantly lower (0.27 U/ml) and remained at that level for the entire observation period. The same pattern was found for alpha 2-antiplasmin. The persistent AT-III deficiency and reduced blood flow associated with polycythemia may explain the increased risk of thromboembolic complications in SGA infants described by others.