Well, you will find that not only the Asian cultures practice this kind of taboo; the Jews and quite a good number of cultures worldwide including those residing in America and Europe are also known to bear this kind of belief. To your surprise, you may find the reason behind the taboo making a lot of sense. 

Before medical science was realized, there were more cases of stillbirths and infant mortality. Most of the dos and don’ts during pregnancy are based on the danger and fear of child loss.

However, the reasons for the belief that buying baby stuff in advance are indeed real. It can be extremely traumatic donating or selling the stuff bought during expectancy, especially for women who experience stillbirth. It becomes even harder to keep the items since they are a reminiscence of sad happenings.  

While it may not be scientifically proven, there is actually some power in the whole belief.

In fact, in the African setting, this is quite unacceptable and you will find women keeping everything to themselves until the arrival of the baby. Most of them argue that shopping for the unborn is likely to set in bad luck and this can be detrimental to both the mother and the unborn.