The great Hungarian music educator, Zoltan Kodaly, once said, "Music education should start 9 months before baby is born."
Prenatal music reminds to be an under-explored field in psychology and music. However, it is quite obvious that music can have positive effects on pregnant women both physiologically and psychologically. The well-being of every mom-to-be is so closely-tied to fetus' development.
I have come across two recent articles on the internet which you may be interested in. One is Familiar Music Can Work Wonders For Your Pregnancy, published in December 2009 and the other is Music during Pregnancy, published in Oct 2008. They both very informative and reliable sources which includes results from clinical experiments.