Several factors can lead to poor hatch rate , fertility:- infertile eggs will not hatch. Quality:- eggs older than 7 days have reduced hatchability. Dirty eggs too might not hatch coz the air space might be blocked by dirt. However don't wash with water too. The size of the bird determines how many eggs to set on the nest. Average 10 eggs. The nest too should not be flat this ensures that all the eggs get warmth. Poor nutrition too might result into poor hatch rate. Always set eggs in the evening and ensure the bird don't leave the nest on day 21 until hatching is complete.