Serial measurements of femoral artery flow velocity waveforms were made at specified intervals of 3 to 4 weeks from 15 to 20 weeks of gestational age to 35 weeks and 1- to 3-week intervals thereafter until delivery in 12 normal fetuses (group 1A) with pulsed Doppler ultrasonography. The pulsatility index of the femoral artery increased linearly with advancing gestation in all 12 fetuses; this was associated with reverse diastolic flow velocity waveforms. In 30 other normal fetuses (group 1B) whose gestational ages ranged between 16 and 38 weeks (mean +/- SD, 29.5 +/- 5.6 weeks), the femoral artery flow velocity waveforms were analyzed with the external iliac artery, internal iliac artery, and umbilical artery waveforms. No significant difference was observed between the pulsatility index of the external iliac artery and that of the femoral artery (mean +/- SD, 3.7 +/- 1.1 vs 3.7 +/- 1.1). The pulsatility index of the internal iliac artery was significantly higher than that observed in the umbilical artery (mean +/- SD, 1.27 +/- 0.28 vs 1.12 +/- 0.23). The femoral and umbilical artery velocity waveforms also were determined in 20 fetuses with intrauterine growth retardation (group 2), whose gestational ages ranged between 24 and 36 weeks (mean +/- SD, 31 +/- 3.4 weeks). Abnormal femoral artery pulsatility index was recorded in two fetuses who died. Absent or reverse flow of the umbilical artery was recorded in 10 fetuses; four of them died, and four others manifested fetal distress or required admission to the neonatal intensive care unit or both. These preliminary data suggest that the femoral artery pulsatility index cannot be used as an indicator of adverse fetal outcome, whereas absent or reverse flow of the umbilical artery seems to be better correlated with adverse fetal outcome.