Objective We sought to determine first- and second-trimester serum soluble Fas (sFas) and placental growth factor (PlGF) levels in idiopathic small-for-gestational-age (SGA) pregnancies. Study Design We measured sFas and PlGF levels in women who delivered SGA infants uncomplicated by preeclampsia and in control subjects. For sFas there were 34 cases and 318 control subjects in the first trimester and 9 cases and 11 control subjects in the second trimester. For PlGF there were 31 cases and 281 control subjects in the first trimester and 8 cases and 11 control subjects in the second trimester. Results SGA pregnancies had lower sFas levels than control subjects in the second trimester (3703 ± 209 pg/mL vs 4562 ± 241 pg/mL; P = .015), but not in the first trimester (4892 ± 191 pg/mL vs 4971 ± 177 pg/mL; P = .68). There was no difference in PlGF levels between SGA and normal pregnancies in both trimesters. Conclusion Serum sFas levels were lower in idiopathic SGA pregnancies in the second trimester, but not in the first. There was no difference in serum PlGF levels in either trimester.