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What is Most significant indicator of fertility is - and explain in detail?
Net reproduction rate 

Net reproductive rate is defined as

"The no. of daughters a new born girl will bear during her lifetime assuming fixed age specific fertility and mortality rates"

It is the only fertility related statistics which also takes mortality rates into consideration.
NRR of one is equivalent to attaining approximately the two child norms.
Goal of NRR=1 can be achieved only if at least 60%* of the eligible couples are effectively practicing family planning.


Gross reproduction rate (GRR): 

Average number of girls that would be born to a married woman if she experiences the current fertility pattern throughout her reproductive span (15-44 or 49 year) assuming no mortality.