Blood flow in the umbilical vessels during third stage of labor was studied in 62 normal-term deliveries. Placental residual blood volume (PRBV) was measured as an indicator of net flow of blood into the infant. By clamping the umbilical arteries separately from the umbilical vein in some, at various times after birth, and comparing the measured PRBV with normal values obtained when all three vessels were clamped simultaneously, it was possible to show indirectly reflected in these PRBV, that blood flows in the umbilical arteries during the first 25 sec after birth, perhaps until 40 sec, became negligible after 45 sec, supporting anatomical evidence of closure at this time, while blood flows in the umbilical vein during the first 3 min of birth, largely influenced by uterine contractions, and became negligible after this time.

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