Fetal hearing.

The fetus can hear during the last trimester of pregnancy. Consistent responses to acoustic stimuli have been observed from 28 weeks onwards. Animal experiments as well as investigations in the human lead to the conclusion that sounds from outside the mother are attenuated, but rarely by more than 30 decibels; external conversations are audible. Only 30% of the phonetic information is available to the fetus, but intonation is almost perfectly transmitted to the amniotic sac. Evidence is accumulating that the mother's voice or different sound patterns from the same voice are learnt by the fetus. Thus there are indications that short-term auditory memory may be present by the end of pregnancy.