Fetal magnetoencephalography: a non-invasive method for the assessment of fetal neuronal maturation

Objective To assess the maturation of auditory evoked cortical responses in the human fetus using fetal magnetoencephalography.

Design Prospective case series over a three-year period.

Setting Antenatal clinics, university hospital.

Population Singleton pregnancies at 29–40 weeks of gestation.

Methods We used a 31-channel-SQUID-biomagnetometer in a magnetically-shielded room to perform fetal magnetoencephalography. To record auditory evoked fields from the fetal brain we applied 500 monotonal bursts generated by a computerised sound generator directly to the maternal abdominal wall near the fetal head. The continuously recorded data sets were analysed stepwise using a specially developed heart artefact rejection software, Fourier filtering, principle component analysis and half split analysis of the averaged data.

Results In 36 of 64 examinations we detected signals of auditory evoked fields comparable to the P2m component in adults. The earliest recording succeeded in the 29th gestational week. The latencies of the auditory evoked responses declined during the third trimester from 300ms to nearly 150ms at term. The maturation of different components of the auditory evoked field could be demonstrated from the 31st gestational week onwards.

Conclusion The maturation of a fetal auditory cortical function using fetal magnetoencephalography could be assessed directly for the first time. We believe that this method will add information to current indirect methods of assessing the normal maturation of the human fetal brain.