RESUMO
OBJECTIVES: To evaluate the neurological maturation of fetuses between 21 and 30 weeks' gestation by the auditory evoked response. METHODS: The auditory evoked responses of 25 normal singleton fetuses were observed once a week from 21 to 30 weeks' gestation. The stimulus consisted of five pulses of sinusoidal waves, for 2 s, at 1500 cycles/s, with a sound pressure of 125 dB. RESULTS: Fetal auditory evoked response increased with neurological maturation, presenting two main points of positive discontinuity. The two points in the heart response were detected between the 24(th)/25(th) and the 27(th)/28(th) week. From the 27(th) week on, fetal motor response (FMR) was always present. Initial fetal heart response presented a fluctuation pattern between the 21(st) and the 30(th) week, with a tendency to increase as gestational age advanced. Fetal heart response also increased with gestational age. Late response (LR) fluctuated until the 29(th) week, and was always present after that period. CONCLUSIONS: The maturation of the fetal nervous system is clearly demonstrated by changes in the auditory evoked responses in different gestational ages, and presents some discontinuity points.
