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"
Superfetation (also spelt superfoetation - see fetus) is the simultaneous occurrence of more than one stage of developing offspring in the same animal. In mammals it manifests as the formation of an embryo from a different menstrual cycle while another embryo or fetus is already present in the uterus.
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