Conception while pregnant.
A condition in which an ovum is fertilised in a woman who is already pregnant.
Fertilization of a second ovum after a pregnancy has commenced; this results in two fetuses of different degrees of maturity developing in the uterus at the same time; also called super-impregnation.
The fertilization of a second ovum some time after the start of pregnancy, resulting in two fetuses of different maturity in the same womb.
The fertilization of two ova in the same uterus at different menstrual periods within a short interval.
The occurrence or formation of a second baby while one is already in the womb; conception that takes place when a woman is already pregnant.