Computerised analysis of unstimulated and stimulated behaviour in fetuses with intrauterine growth restriction. 
Unstimulated (passive) and stimulated behaviour, in the form of fetal heart rate (FHR) and activity (FA)) was studied in 32 normal fetuses and 14 fetuses with intrauterine growth restriction (IUGR).  FHR and FA were recorded using a single 1.5 MHz ultrasound transducer and analysed by computer.  A 5 s vibroacoustic stimulus (VAS) (electronic artificial larynx) was used for the stimulation studies.  The IUGR fetuses had significantly different patterns of both unstimulated and stimulated behaviour compared to normally grown fetuses.  When unstimulated they had lower FA rates than the normally grown fetuses but this was only statistically significant at 28-31 weeks.  They also spent a significantly lower proportion of time exhibiting high FHR variation at 28-31 weeks.  Following VAS the IUGR fetuses had lower FA responses at all gestations and lower FHR responses from 32 weeks, though only the differences in FA response at 28-31 weeks were statistically significant.  Of the 14 fetuses with IUGR, all but one exhibited passive behaviour (ERR and/or FA) that was outside the 10-90th range, for normally grown fetuses, whilst 6 of the 14 had responses to VAS that were within the normal range.  We do not feel that computerised assessment of stimulated behaviour in preterm IUGR fetuses confers any advantage over passive observations.