I just finished a semester in Child Development Psychology this year and I learned that this theory is true
. Unborn babies are able to hear their environment (it's a survival skill they pick up so they can identify their mother by her voice when they're born). As a result, if a repetitive melody is played over and over, they will be able to identify it the same way the identify their mother's voices.
Good luck with your new baby and hopefully he/she becomes an Ayu fan too
!