I can DNA gender test as soon as they hatch (I did that with Bert and Betty), I make sure I know which egg is from which chick.Oh, definitely a major drawback. Painful for us to pay for DNA-sexed Silkies but there's no re-homing roos in the city.
The only time we ever had true baby chicks were the auto-sexed Dominique chicks where we could pick out the female babies from the feed store bin.
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Dry out the egg, making sure the inner membrane is with the egg. And then send it to the lab.
Couple days later I know the gender

But I need to be there and get the egg and chick matched up. Easy with only 2 chicks!