superfetation

noun2

1. •
   The formation of a fetus while another fetus is already present in the uterus.
2. •
   An excessive accumulation; a superfluous addition.

   • These gentlemen were greatly astonished at Bovary's romantic ideas, and the pharmacist hurried in to say to him: "This velvet looks to me rather a superfetation. Besides, the expense..." — 1992