Estimation of fetal oxygen uptake in human term pregnancies

Abstract

Objective. Umbilical oxygen (O2) uptake is a parameter of basic physiologic interest. It has been extensively studied in chronically catheterized animals but very few data have been obtained acutely in humans. Recent developments in ultrasound technology allow the estimation of umbilical venous blood flow in utero.Methods. In all, 26 normal term pregnancies were studied at the time of elective cesarean section in order to evaluate fetal O2 uptake as the product of umbilical blood flow and umbilical O2 veno-arterial difference. An ultrasound evaluation was performed within 1 h from delivery: umbilical vein area and flow velocity were recorded to calculate umbilical vein volume flow (Qumb). Blood samples from the umbilical vein (uv) and artery (ua) were obtained at the time of fetal extraction for respiratory gases and acid–base evaluation.Results. Umbilical O2 uptake was calculated as Qumb • (uv-ua)O2 content: an average value of 0.84 ± 0.40 mmol/min was obtained. Umbilical O2 uptake per kg was 0.25 ± 0.12 mmol/kg/min, significantly related to fetal O2 delivery.Conclusions. We estimated umbilical blood flow by ultrasound and we measured umbilical O2 uptake at term obtaining a value of umbilical O2 uptake/kg similar to what previously reported in human pregnancies and chronically catheterized animals.