What exactly is a fertilized egg?
A hen lays eggs irrespective of the presence of a rooster. The chicken eggs are only fertilized if the rooster has mated with the hen, this has to happen before the egg is formed. Therefore, any egg that a hen lays before she mated is unfertilized but if a hen has mated, then the egg would be fertilized. Even if an egg has been fertilized, once it goes into the fridge, no development takes place of the embryo. It is said that if a hen has mated once, then for an entire week, she will lay fertilized eggs.
Many people said fertilized chicken eggs are healthier and contain more nutrition value. And people are saying that eating fertilized eggs can nourish treatable blood deficiency and dysmenorrhea. However it is still a highly debatable topic.