Comparison of unstimulated and stimulated behaviour in human fetuses with congenital abnormalities.

Unstimulated (passive) and stimulated behaviour [fetal heart rate (FHR) and movements (FA)] was studied in 32 normal fetuses and 10 fetuses with congenital abnormalities (CA). FHR and FA were recorded using a single 1.5-MHz ultrasound transducer and analysed by computer. A 5-second vibroacoustic stimulus (VAS) ('electronic artificial larynx') was used for the stimulation studies. Thus, passive and stimulated behaviour could be studied in a group of fetuses with known pathologies. One hour was used as the recording time for the passive studies and 20 min for the stimulation studies (10 min pre- and 10 min post-VAS). All CA fetuses had abnormalities of FHR and/or FA on recording passive behaviour compared to normal fetuses. However, 4 of the 10 fetuses with CA had responses to VAS that were within the normal range for both FHR and FA. We do not feel that computerised assessment of stimulated behaviour in fetuses with CA confers any advantage over analysis of passive behaviour.