Section 20 and 21 of Transfer Of Property act 1882

When Unborn Person Acquires vested Interest On Transfer For his Benefit ?
  When an Interest is created for the benefit Of an Unborn Person

  He Will Acquire vested interest On His Birth

  Even Though the Possession is not Transfer to him immediately  on his birth according to the deed of transfer

  Or the deed imposed a condition that the unborn child would  get interest on the age of majority

What is Contingent interest 

When an interest is created in favour of a person with
a condition which is uncertain or the interest will be transfer on the happening  or not happening of an uncertain event is called contingent interest.

Salient Features Of Contingent  Interest 
 Contingent Interest is not vested but vest on happening of event  in Future
  The event is Uncertain
   to acquire such interest is depend on the future accident if such accident is not happened no right will be created
    when the Transferee  died before the happening of the event the transfer will fail
 
  Exceptions , When a condition is made that the interest will be transfer to the person upon attaining particular age is not contingent

Distinction Between Vested And Contingent Interest 
The Title of owner is perfect while in contingent interest it is not perfect and become perfect only on happening of uncertain event.

The interest is absolutely In vested interest   while  the contingent interest is conditional .


On the date of transfer it become effective while contingent interest only become effective on happening of uncertain event .

The vested interest is inheritable while contingent  is defeated on the death of the person if the uncertain event is not happened

The vested interest  can be transfer absolutely while the  contingent is transfer only with the uncertain condition