superfetation

Từ điển WordNet v3.1 - WordNet Dictionary

noun

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
• Derivationally related forms:
superfetate
• Hypernyms:
fertilization, fertilisation, fecundation, impregnation