A method for serial sampling of umbilical artery blood was described in a previous report. Another study using this method demonstrated that the umbilical artery blood becomes more asphyxial over the first 20 sec after birth, even though up to 5 breaths occurred over this time. In the present study, serial samples of umbilical artery blood were function obtained at slightly later intervals; the first samplings occurred at 11–41 sec and the second samplings at 22–59 sec. From 3 to 11 breaths occurred between birth and the second sampling. Unlike the results in the prior study, many infants showed a rising pH, a falling PCO2, and a rising oxygen saturation from the first to the second sampling. When the results of one of the prior studies are combined with the present study, it appears that the fifth breath represents the approximate point of reversal of the trend from one of increasing asphyxia to one of improvement in blood gas values. The fifth breath usually occurred at 20–30 sec. It may be advantageous to allow the placental respiration to continue until the pulmonary respiration becomes effective by delaying cord clamping until 5 breaths have occurred or until 30 sec have elapsed.
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