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

Placenta can be defined as germination of seed. When fruit is hanging on mother plant. Plant growing on marshy - muddy land is called mangroves. When seeds of these plants fall on marshy land, they dont grow because there high salinity and more water condition exists.

So plants in which germination of seed occurs they are attached to mother plants. In waste generally younge ones of animals at a time take birth in $3$ to $8$ number.

Placenta automatically keeps the birth of young ones in waste very limited because eggs or egg cells are produced in limited number and fertilise during reproductive cycle of female.