The current role of intrapartum fetal blood sampling.

Abstract

Fetal blood sampling with determination of pH and base excess is a valid and useful supplement to continuous FHR monitoring. When used in conjunction with the conventional methods of FHR interpretation, FBS can improve the accuracy of determination of the truly asphyxiated fetus, having a potentially ominous FHR pattern. Thus, its use may postpone or prevent the unnecessarily expeditious delivery of fetuses who are in fact not asphyxiated. Despite this usefulness, FBS has diffused poorly into the great majority of obstetric services in the United States, primarily because of the minor, though real, technical inconveniences and analytic difficulties. Many defenders of FHR monitoring feel that its use without the availability of FBS is responsible for the overdiagnosis of fetal distress and the subsequent increase in cesarean section rates. There are two possible ways out of this dilemma. First is the development of a simple method of continuously recording fetal tissue pH. Though there are such devices, they do not yet satisfy the necessary criteria of facility and simplicity, but improvements may be expected within several years. A second approach is to improve the accuracy of FHR interpretation, either by the application of available knowledge or by improvement in the understanding of FHR through further investigation. As to the application of presently available knowledge, avoidance of overcalling the presence of fetal distress could be facilitated by universal acceptance of the high prognostic accuracy of normal FHR variability to predict a vigorous fetus, even in the presence of other so-called ominous FHR patterns. Only a small number of fetuses, probably less than 1% in most populations, have FHR patterns with absent or decreasing variability with periodic changes that cannot be ascribed to drugs or other nonasphyxial causes. Part of this small group may unnecessarily go to cesarean section for fetal distress in the absence of FBS, but its influence on overall cesarean section rates will be minor.