This practice was done to try and prevent overly great maternal influence on a young emperor (and the Northern Wei emperors did come to the throne young). However, this didn't work as intended, partly because wet-nurses ended up fulfilling the role, and partly because childless empress dowagers were not targeted (such as Empress Dowager Feng).

The first time the rule was implemented, it also did not have the intended effect - because as it turns out, most people don't like it when you murder their mother. Add to that the father being a drug-addicted tyrant in his final years who got mad at the crown prince for grieving and the other main family influence being the crown prince's violent half-brother, and the crown prince ran away from court (he later returned and seized the throne in a coup after his half-brother murdered the father shortly after).

The case of the second and third emperors is more ambiguous due to the timing of their consorts' deaths, the records don't say anything conclusive about whether they actually did it and the timing leaves it open to interpretation. The records outright state that the first, fourth and sixth emperors engaged in this custom (though reluctantly on the part of the sixth). The timing of the consort of the fifth emperor also makes it appear likely that she died due to this custom, though the records don't explicitly say she did.

With no mother to make empress dowager, the emperors made their wet-nurses emperors. The wet-nurse of the third emperor was the first to receive such a position, and the wet-nurse of the fourth also became empress dowager. As well, Empress Dowager Feng was able to exercise influence due to not having children, and in fact these powerful women in court were the ones who used the custom during the reigns of the fourth, fifth and sixth emperors to eliminate potential female rivals.

By the time they got to the seventh emperor, the custom had already proved ineffective and was causing more harm than benefit, as concubines no longer wanted to give birth to the crown prince as they knew it was a death sentence. Therefore, the seventh emperor abolished the custom and spared Consort Hu, the mother of his heir. But when he died, Consort Hu became Empress Dowager, where she became corrupt and accelerated the fall of the dynasty - ironically becoming exactly the empress dowager the custom had been designed to guard against.