The reason why the Mus had some of his specimens in the private sperm bank was that they were meant to be used for artificial insemination when Yun Shishi was selected to surrogate for them seven years ago. Alas, due to her poor health, they eventually opted for another method. The man himself had forgotten about those sperms.
Thanks to his niece, he was reminded of this hidden, potential danger and had all his sperms destroyed this time.
What was laughable was that Mu Yancheng's sperms, which had replaced his, were not of great quality. Because of this, the young missy, who was completely in the dark, suffered a good deal while trying to conceive a child.
With the IVF-ET procedure being rather laborious and painful, the one undergoing it naturally had to go through a great deal of pain.