Check out this great article :
10 facts about fertile chicken eggs.
Including how you can tell, what you can do with them and whether they’re safe to eat.
Ever wondered how you can tell whether or not an egg is fertile?
Do you worry about eating chicken eggs in case they have the beginnings of a chick inside?
Or have you heard that eating fertile eggs is healthier for you?
There are lots of myths in the world of backyard chicken-keeping about eggs and fertility.
The weirdest I’ve seen is that you can tell whether an egg is fertile by swinging a needle suspended on cotton above the egg. It’s a twist on the myth that you can tell the gender of a human baby by the same method.
If only it were that easy!
In this article, the auther covers the facts about chicken eggs and their fertility, based on questions I’ve been asked over the years and answers from both my own experience and from respected sources https://www.raising-happy-chickens.com/fertile-chicken-eggs.html