What are the consequences for the baby ? Are there any studies that would have noticed positive / negative consequences on the baby of the vibrations a classical guitar induces on the belly and the chest ?
Should the avoid playing dissonant chords ? Playing loud ? Playing notes that would be near the resonance frequency of her belly ? (frequency that should get lower and lower as the belly gets larger)
This is a positive thing. Studies have shown the positive effect music has on unborn babies, see: Whitwell, Giselle E. "The importance of prenatal sound and music." Journal of Prenatal and Perinatal Psychology and Health 13 (1999): 255-262.
In the case of a catastrophic fall from 20 feet in height, A mother's body will protect the unborn child from harm. The mother might not survive, but the baby likely will. Given that, I find it impossible to imagine how playing classical guitar could harm the baby.
When my wife was pregnant, she used to sit on my bass amplifier as I was playing, which would make the baby rouse and kick. That baby went on to become an extremely intelligent adult with absolutely no rhythm. :)
The only possible downside to playing classical guitar while very pregnant is posture difficulties for mom.
