Effect of vacuum extraction on umbilical cord blood acid-base measurements.

The objective of this study was to determine whether vacuum extraction is associated with umbilical cord blood acid-base changes when used electively or in the presence of suspected fetal distress. Data from 1,428 patients from a previously published randomized trial of intrapartum electronic fetal heart rate monitoring versus intermittent auscultation were analyzed to identify differences in umbilical cord blood acid-base measurements associated with the elective use of vacuum extraction (patients with duration of second stage of labor 60 min or less) and also in the presence of suspected fetal distress during the second stage of labor. When used electively, vacuum extraction was associated with lower pH (in both umbilical cord artery and vein), lower venous base excess, and higher venous carbon dioxide tension (PCO2), as compared to normal spontaneous vaginal delivery. After correcting for duration of second stage of labor, elective vacuum delivery was significantly associated only with a decrease in cord venous pH and increase in venous PCO2. However, these cord blood acid-base changes were not accompanied by any differences in perinatal morbidity and mortality or in the number of neonates born with acidemia (cord arterial pH < 7.15 or < 7.10). In cases of suspected fetal distress, the use of vacuum extraction was not associated with any detectable cord blood acid-base changes as compared to normal spontaneous vaginal delivery. These data support the continued use of vacuum extraction, especially in cases of suspected fetal distress during the second stage of labor.