The presence of fetal glucogenesis was evaluated in nine patients with pregnancies complicated by intrauterine growth retardation (IUGR) at the time of fetal blood sampling (FBS) between 29 and 35 weeks of pregnancy. Eight were singleton pregnancies and one was a twin pregnancy in which blood samples were obtained from both twins. A maternal primed-constant infusion of D(U-13C]glucose was performed, and the presence of fetal glucogenesis was assessed by a comparison of steady-state maternal and fetal glucose enrichments. No significant difference was present between maternal and fetal molar percent excess ([MPE] P = .97), and the mean fetal to maternal (F/M) MPE ratio (0.99 +/- 0.01) was not significantly different from 1 (P = .76). F/M MPE ratio was independent of the time of FBS and umbilical venous glucose and lactate concentrations. Thus fetal glucogenesis is not demonstrable in a group of fairly severe growth-retarded fetuses after an overnight fast with this relatively noninvasive approach.