From what we have discovered, we know that the motherís voice and other outside sounds are not perceived in the same way as we hear them. The soft tissue from the motherís abdominal wall and the inside of her body absorb the sound waves, decreasing their intensity and creating a distorted sound. It is as if the fetus were surrounded by pillows, or like when we hear someone talking in the next room, but are unable to make out what they are saying.
According to a study done on gestating sheep and published in 1996, words spoken externally and recorded from inside the womb were only about 50% intelligible (Griffiths et al, Journal of the Acoustical Society of America).
The fetus is said to perceive primarily low tones because higher sounds are buffered even further.
If the fetus is to hear the same as we do, it can only be achieved intravaginally.
The vagina is a closed space, thus preventing sound dispersion. The layers of soft tissue separating the fetus from the origin of the sound are fewer: there are only the vaginal and uterine walls.
By placing a speaker inside the vagina, the fetus can perceive the sound at nearly the same intensity with which it is being emitted.
We can use any melody or voice during Babypod ultrasounds; even so, we recommend using songs that are available on our playlists to obtain a high level of foetal response.