My gold sex links - or one of them, anyway - laid a few doubles when they first started laying last fall. They were HUGE, I don't know how the hen got them out! I was told it's a glitch in the developing reproductive system and would likely stop as the hens matured. So far, that's been right. The girls are 11 months old, almost, and I haven't had a double yolk since last fall. They started laying young, too - the day after they turned four months old! So I guess they were due for a couple of glitches! I still get some eggs so big I can't close the cartons, but they haven't been doubles.