Response of the foetal pupil to vibro-acoustic stimulation: A foetal attention test

BackgroundThe iris regulates the intensity of light that stimulates the retina. The pupils dilate also in response to mental activities as sign of attention. We hypothesized that the response of the foetal pupil to vibro-acoustic stimulation (VAS) reflects foetal attention.AimsTo determine whether the changes in the foetal pupil produced by vibroacoustic stimulation is a sign of foetal attention.Study designWe studied sonographically the pupils and iris of 151 foetuses between 27 and 41 weeks of gestation, using maximum ultrasonic zoom.Subjects160 human foetuses between the 27th and the 41st week of gestation.Outcome measuresThe diameters of the pupil and iris were compared before and after VAS.ResultsAt baseline, the pupils were miotic. We observed a response to VAS, manifest as a prominent pupillary dilatation in all foetuses. At all gestational ages, the percent increase in pupillary diameter was ≥ 57% (mean 87%; range: 57–135%).ConclusionsVAS dilated the foetal pupil. Sonographic assessment of the foetal pupil provided important insights in the development of foetal neurological functions.