Detection of fetal auditory evoked responses by means of magnetoencephalography

MagnetoEncephaloGraphy (MEG) is proposed as a non-invasive technique to det ect the physiological activity of fetal brain, due to its ability to record brain activity without direct contact with the head and the transparency o f magnetic signals in passing through extracerebral fetal layers and the mo ther's abdomen. Healthy women with uncomplicated pregnancies and fetuses in breech presentation were examined; gestational ages at time of study range d between 36 and 40 weeks. In order to evaluate fetal well-being, ultrasoun d and cardiotocographic data were assessed a few days before and after MEG recording sessions. The participating women were placed in a semi-reclining position in a magnetically shielded room: here the presentation of the fet us and precise region of the mother's abdomen corresponding to the fetal he ad were determined by ultrasound investigation in order to place the MEG de tecting system as near as possible to the fetal brain. MEG recordings were performed by means of a 28-channel neuromagnetic system. Every MEG recordin g session was performed during the acoustic stimulation of fetuses, in orde r to detect the cerebral events evoked by peripheral stimuli. The auditory stimuli were delivered from a plastic tube placed on mother's abdomen, near the fetal head, and consisted of a 300 ins 103 dB pure tone at 500 and 100 0 Hz, presented at a 0.4 c/s repetition rate. In six cases following accura te digital subtraction of maternal and fetal electrocardiographic (EKG) sig nals we remained with a stimulus-related response peaking at about 250 ms; this was considered to originate from the fetal brain. In favour of this in three cases a clear dipolar distribution was evident at the peak of brain response centered on the fetal head and consistent with a brain generator. Despite several technical problems requiring solution before a possible rou tine clinical application, MEG has been found to be suitable for the non-in vasive exploration of the fetal brain. (C) 2001 Elsevier Science B.V. All r ights reserved.