Fetal habituation to vibroacoustic stimulation in relation to fetal statesand fetal heart rate parameters

Objectives: Fetal habituation to repeated stimulation has the potential to become a tool in the assessment of fetal condition and of the function of t he fetal central nervous system (CNS). However. the influence of fetal quie scence and activity on habituation remains to be clarified. We studied habi tuation and the influence of fetal start: and fetal heart rate (FHR) parame ters on habituation in healthy term fetuses. Subjects and method: We studie d habituation in 37 healthy fetuses in two teats with an interval of 10 min . The vibroacoustic stimuli were applied to the maternal abdomen above the fetal legs for a period of 1 s every 30 s. A fetal trunk movement within 1 s after stimulation was defined as a positive response. Habituation rate is defined as the number of stimuli applied before an observed non-response t o four consecutive stimuli. The FHR patterns (FHRP) of the 10 min observati on period before and after the tests were visually classified. Fetal states were defined according to the FHRP. Baseline FHR, FHR variability and the number of accelerations were calculated in a subgroup of 25 fetuses. Result s: Of the 32 fetuses that responded normally during the first test, 26 habi tuated and six had persistent responses. The median habituation rate decrea sed significantly in the second test (P = 0.001). There was no difference i n habituation rate between fetuses that where initially in a quiet state an d those in an active state. The FHR parameters before the first test and th e difference between these FHR parameters before and after the test did not correlate with the habituation rate. Conclusions: Although the majority of healthy fetuses was able to habituate, the interfetal variability in habit uation performance is such that testing of habituation seems not to be a se nsitive tool for the assessment of the fetal CNS. This variability is neith er the result of differences in fetal state nor of the various FHR paramete rs before testing, nor of the difference in change of FHR parameters arisin g from stimulation. (C) 2001 Elsevier Science Ireland Ltd. All rights reser ved.