Vivipary automatically limits the number of offsprings in a litter. How?

(A) Vivipary is a reproductive strategy where the embryo develops inside the mother's body,receiving nourishment directly from her. In mammals,this is facilitated by the placenta.
Because the development of the fetus requires significant metabolic resources and energy from the mother,the female body can only support a limited number of offspring at one time.
This biological constraint ensures that the mother can provide adequate nutrition and protection to the developing young,thereby limiting the litter size to a sustainable number,typically ranging from $1$ to $8$ depending on the species.