Fetal heart rate response to scalp blood sampling

Fetal heart rate acceleration in response to various stimuli has long been considered to be a reliable sign of fetal well-being in both the intrapartum and antepartum periods. In an effort to define the correlation between fetal heart rate response and fetal blood pH, we analyzed 200 fetal heart rate tracings of fetuses who had undergone scalp blood sampling in early labor. Data in regard to fetal heart rate response to endoscope placement, scalp puncture, and resultant scalp pH were then analyzed. In no case did a fetus with a scalp blood pH less than 7.20 respond to scalp puncture with an acceleration (defined as an elevation above the baseline of 15 bpm for at least 15 seconds). Among fetuses with a scalp blood pH greater than 7.28, 142 of 144 responded to scalp puncture with an acceleration. Exception occurred in one fetus who was 32 to 33 weeks' gestation, and in one fetus who was moderately Rh isoimmunized. Fetuses with scalp pH in the range of 7.21 to 7.28 showed a variable response. The correlation noted between a reassuring fetal heart rate pattern and the absence of acidosis in conjunction with the inverse (73% of fetuses in whom no acceleration occurred were acidotic) is further verification of both the reliability and complementary nature of intrapartum fetal assessment by both biophysical and biochemical techniques.