superimpregnation

su·per·fe·ta·tion

(sū'pĕr-fe-tā'shŭn),

The presence of two fetuses of different ages, not twins, in the uterus, due to the impregnation of two ova liberated at successive periods of ovulation; an obsolete concept.

Synonym(s): hypercyesis, hypercyesia, multifetation, superimpregnation