wrote:

Are there any same sex twins that were "bi-chorial" with two separate
placentas and "BI-amniotic" with two separate amniotic sacs, and later DNA
tested later and proved to be identical in this news group. I wonder how
common it is.

I don't know about the stats here, but I have read in several places that 1/4
to 1/3 (the exact numbers vary, but in general a substantial fraction) of
identical twins have separate placentas/chorions.

Mind you, the medical records aren't always that trustworthy either. I don't
think they would record two placentas when there was really only one, but my
kids are recorded as sharing a placenta when they're fraternal as all heck.

--Helen