Umbilical cord blood gases - a sampling effect

Umbilical cord blood gas analysis provides objective evidence of neonatal condition at birth; a particular utility of the test is to identify those babies who have suffered significant oxygen deficit prior to delivery. Traditional obstetric practice is to clamp the umbilical cord within seconds of delivery but some experts now recommend a delay of 2–3 minutes.

Clinical researchers at Malmö University in Sweden have demonstrated that cord blood gas results are significantly influenced by this delay in umbilical cord clamping. Umbilical cord arterial and venous blood was sampled from 70 full term babies at the moment of birth and then again at 45 and 90 seconds later.

Blood gas analysis of these samples revealed that mean arterial blood pH fell from 7.24–7.21 over the 90 second period; mean arterial pCO₂ increased from 7.64–8.07 kPa and mean arterial pO₂ increased from 2.3–2.74 kPa. Change of very similar magnitude occurred in venous pH and pCO₂, but venous pO₂ remained unchanged.

The group also demonstrated increase in lactate concentration: 5.3–5.9 mmol/L for arterial blood and 5.0–5.3 mmol/L for venous blood. The authors conclude that “delayed cord clamping results in significantly different measured values of cord blood acid-base parameter.”