Volumetric flow in the umbilical artery: normative data

OBJECTIVE: Provide normative data for the volumetric blood flow (cc/min and cc/min/kg) in the umbilical artery. METHODS: Flow was determined from an umbilical artery in 252 normal obstetrical patients from 18-40 weeks' gestation utilizing pulsed Doppler and color flow Doppler with an angle of insonation of 30-60 degrees. Simultaneous velocimetry studies (S/D ratio, resistance and pulsatility indices), fetal biometry, and an anatomic survey were obtained to further define the normal population. RESULTS: There was a steady increase in the flow (cc/min) in the umbilical artery as pregnancy progressed. Flow/kg showed a steady decline as fetal weight increased. Umbilical artery diameter increased until reaching a plateau at 32-34 weeks. Velocimetric results were consistent with known data. CONCLUSIONS: Volumetric blood flow in the umbilical artery can be determined with relative ease and normative data from 18-40 weeks is presented for the first time.