Why do chicks die during incubation?

[jonty]

Why do chicks die during incubation? I incubate 20 eggs at at time but only get a hatch rate of may be 50% When I check the eggs 90% were fertile and had the start of a chick and in some cases it looks like the chick die late into incubation.

 

[gabrielle1976]

I am shure some E G G expert will tell you more details , But I am guessing there are a LOT of reason , to low or high of heat, to low or high of huimidity , genetics , malformations, ect ect ect