Superfetation

n.

1.

(Physiol.) The formation of a fetus at the result of an impregnation occurring after another impregnation but before the birth of the offspring produced by it. This is possible only when there is a double uterus, or where menstruation persists up to the time of the second impregnation. In then became a superfetation upon, and not an ingredient in, the national character. - Coleridge.

Noun

1.

superfetation - fertilization of a second ovum after a pregnancy has begun; results in two fetuses of different ages in the uterus at the same time; "superfetation is normal in some animal species"

fecundation, fertilisation, fertilization, impregnation, superfetate