Background Delayed cord clamping (DCC) effects both cardio-pulmonary transition and blood volume in neonates. Understanding the circulation through the umbilical vessels immediately after birth, with cord and placenta intact, is important.

Objective To describe the duration and patterns of blood flow through the umbilical vessels during DCC.

Methods Arterial and venous umbilical blood flow was measured during DCC using Doppler ultrasound in a prospective, observational, study of uncomplicated term vaginal deliveries. Immediately after birth, the probe was placed in the middle of the umbilical cord and the pattern and duration of flow in the vein and arteries evaluated until cord clamping.

Results Thirty infants were studied. Venous: In 10% there was no flow, in 57% flow stopped at a median (IQR) min:sec of 4:34(3:03–7:31) after birth before cord was clamped, and in 33% flow continued until cord clamping at 5:13 (2:56–9:15). Venous flow was initially intermittent (100% increase during large breaths, stopped/reversed during crying), but became continuous. Arterial: In 17% there was no flow, in 40%, flow stopped at 4:22(2:29–7:17), while cord pulsations were still palpable. In 43% flow continued until cord was clamped at 5:16(3:32–10:20). Arterial flow was pulsatile, unidirectional towards placenta or bidirectional to/from placenta. In 40% flow became almost continuous (non pulsatile) later after birth.

Conclusion During DDC venous and arterial umbilical flow occurs for longer than previously described. Net placental transfusion is probably the result of several factors of which breathing could play a major role. Umbilical flow is unrelated to cessation of pulsations.