I thought I had quoted Walnut too about the pullet eggs/double yolkers....I'm on my phone and pics are hard enough to load, not going to try to figure out how to add her quote...
The dark circle on the egg is just my "O" for turning purposes. But those big eggs were almost twice as big as what I've been normally getting. Even for the hens. I wonder if it because I switched to layer feed?
On an obscure egg shell, it may not be possible to detect a double yolker. But with a translucent shell and a good light, you can readily see two yolk shadows, and if you've started incubation, you will see two dark spots and two sets of blood vessels.
They will never be "identical twins" as two eggs and two sperm are involved. I had a turkey egg go full term with twins but since I wasn't home to to a full on assist I lost them.