I believe the influence of sounds in the womb relates to language acquisition, not to whether they are nurturing.
As far as actual nutrition during pregnancy is concerned, I read when I recently got seriously into this (again, don't make me cite sources, we're just having a conversation here, right?) that it is the quality of nutrition before, not during pregnancy that counts. Children born during famine do not show much impairment. Children born to mothers who have lived through famine but born after the fact show a lot.