Ok, to me, a bellyshirt seems to have two functions: Comfort and/or as a device to appear more attractive, perhaps explicitly so. Attractiveness is understandably important to her (It's not like pregnancy makes you not-human), but to me, a belly shirt at least borders on being a sexual incentive, which is why i feel it is out of place. Comfort could indeed be the answer, and if that is the case, well, alright, my analysis was bullshit. (I would try to keep my baby warm, but I guess it can get pretty hot in Japan)

Pop-psychology...