Fetal habituation to vibroacoustic simulation in uncomplicated postterm pregnancies

Objectives: Testing of fetal habituation to repeated vibroacoustic stimulat ion might give additional information concerning the fetal condition and ce ntral nervous system (CNS) functioning in postterm pregnancies. This study is designed to investigate whether healthy postterm fetuses are able to hab ituate and if so, if the habituation pattern of postterm fetuses differs fr om that of term fetuses. Study design: Twenty women with an uncomplicated p regnancy beyond 41 weeks gestational age (GA) participated; and 37 women wi th a GA between 37 and 40 weeks served as controls. The vibroacoustic stimu lus was repeatedly 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 of stimulus application was considered a positive response. Lack of response to four co nsecutive stimuli indicated habituation. The habituation rate is defined as the number of stimuli applied before the fetus stopped responding. Data we re compared using Mann-Whitney U test. Results: Of the 18 postterm fetuses in which the presence or absence of habituation could be established, 14 ha bituated and four persisted in responding. Twenty-six of the 32 term fetuse s, in which the presence or absence of habituation could be established, ha bituated and six persisted in responding. The habituation rate varied widel y in postterm (median of eight stimuli, quartile ranges of 6 and 18) as wel l as in term fetuses (median of 9.5 stimuli, quartile ranges of 6 and 15). There was no difference in median habituation rate between postterm and ter m fetuses. Conclusion: The ongoing maturation of the CNS in the last weeks of pregnancy appears not to be reflected in the fetal habituation pattern. Furthermore, the interfetal variability in habituation of healthy postterm fetuses is such that testing of habituation appears not to be suitable for the identification of the fetus at risk for an adverse neonatal outcome. (C ) 2001 Elsevier Science Ireland Ltd. All rights reserved.