Do bird eggs grow during incubation?

i have two birds who recently mated. (i was surprised that they mated at such an old age) the eggs are beatiful! My bird gets really defensive when i come near, but lately she has not been laying on her eggs. I have been taking care of them by myself. i need to know, because i think they will not hatch. I think they will not hatch because the eggs arent becoming bigger. Help??????