superfetation

noun

1. (countable, uncountable)The formation of a fetus while another fetus is already present in the uterus.
2. (countable, uncountable)An excessive accumulation; a superfluous addition.

   “1992, Geoffrey Wall, translator of Gustave Flaubert, Madame Bovary 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..."”