Estimation of fetal oxygen uptake in human term pregnancies

Umbilical oxygen (O(2)) 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.

In all, 26 normal term pregnancies were studied at the time of elective cesarean section in order to evaluate fetal O(2) uptake as the product of umbilical blood flow and umbilical O(2) 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 (Q(umb)). 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.

Umbilical O(2) uptake was calculated as Q(umb) • (uv-ua)O(2) content: an average value of 0.84 ± 0.40 mmol/min was obtained. Umbilical O(2) uptake per kg was 0.25 ± 0.12 mmol/kg/min, significantly related to fetal O(2) delivery.

We estimated umbilical blood flow by ultrasound and we measured umbilical O(2) uptake at term obtaining a value of umbilical O(2) uptake/kg similar to what previously reported in human pregnancies and chronically catheterized animals.