Reliability of fetal buttock blood sampling in assessing the acid-base balance of the breech fetus.

This prospective investigation was undertaken to compare fetal buttock capillary blood pH and umbilical artery and vein pH in fetuses presenting by the breech. The study group comprised ten term patients with singleton fetuses in the frank breech presentation who met established criteria for vaginal breech delivery. All patients had a normal labor pattern. Eight fetuses had a normal fetal heart rate tracing and two had severe variable decelerations during the second stage of labor. We obtained capillary blood for pH measurement from the fetal buttock within 15 minutes of delivery. Immediately after delivery, we collected arterial and venous blood samples from the umbilical cord for measurement of pH. In all fetuses, there was a highly significant correlation between fetal buttock capillary blood pH and umbilical artery pH (r = 0.96; P less than .001) and umbilical vein pH (r = 0.88; P less than .001). We conclude that measurement of pH in capillary blood obtained from the fetal buttock provides accurate assessment of the acid-base status of the breech fetus.