How about "sex determined at birth", or possibly "sex confirmed at birth" for babies who had their chromosomes checked in utero for some reason.
Here's the real point, for those individuals who believe they were "assigned" the wrong gender at birth. PROVE IT WITH A CHROMOSOME CHECK.
You think you're a woman even though the doctor said you were a boy and you have a penis? Fine, pony up the scratch for a chromosome test, and if it comes back "XX", we'll talk about getting you a "chopitoffame" operation.
You think you're a man even though you menstruate? Fine, same deal, if your chromosomes come back "XY", we'll talk about an "addadicktome".
And for those unfortunate souls with true chromosomal abnormalities like "XXY", they warrant special care.
But we gotta stop encouraging the crazies.
It really is sex at conception. The baby’s sex. Period.
“Sex confirmed at birth” makes sense, since sex is determined well before, with ultrasound.