Developmental changes of auditory-evoked fields in fetuses.

Fetal magnetoencephalography (fMEG) could be a viable noninvasive tool to investigate the development of neuronal functioning in the unborn by means of the maturation of cortical auditory-evoked fields (CAEF). The earliest successful recording of a CAEF component was performed at the gestational age of 27 completed weeks with an observed peak latency of 294 ms. Several different components could be differentiated in the CAEF complex. They were classified in accordance with a nomenclature introduced for cortical auditory-evoked potential (AEP) components in preterm neonates. During the third trimester of pregnancy, the detection of any component was successful in 77% of the cases. The detection rates for the different components observed were P1pm 31%; N1pm 21%; P2pm 27%; N2pm 39%; and P3pm 27%. The development of fetal CAEF is described both intraindividually in longitudinal observations and interindividually by grouped comparison throughout the second half of the pregnancy in the largest series of subjects in the literature. The components P2pm and N2pm show a significant negative correlation of their peak latencies with increasing gestational age (P < 0.05). fMEG allows to observe the development of a parameter of prenatal cortical function that can be interpreted as maturation. The results are in good accordance with those obtained in newborn EEG studies in preterm neonates.