Demonstration of fetal habituation and patterns of fetal heart rate response to vibroacoustic stimulation in normal and high-risk pregnancies.

Habituation is the decremental response to repetitive stimulation and is a learned response. One hundred five fetuses from 26 normal and 79 high-risk pregnancies were evaluated from 28 to 43 weeks' gestation and in labor as to the fetal heart rate response from repetitive vibroacoustic stimulation. Four patterns were observed: (1) habituation (H), (2) reactive nonhabituation (R-NH), (3) accelerative nonhabituation (A-NH), and (4) nonreactive (NR). Fetuses from normal pregnancies habituated significantly more often than those at greater risk. Of the high-risk group, only 6.4% who have habituated antenatally had a labor or nursery complication compared with 67.5% who exhibited the R-NH or A-NH pattern (P less than .001). This study has demonstrated the patterns of FHR response to vibroacoustic stimulation, as well as the ability to induce fetal habituation. Habituation may differentiate high-risk fetuses on the basis of labor complications or poor neonatal outcome. Further study of habituation is being conducted to ascertain if it should be added to standard fetal surveillance modalities of fetal movement, the non-stress test, contraction stress test, and biophysical profile.