Originally Posted by TexasRN
If the embryo splits before implantation into the uterine wall, there will be 2 placentas and 2 amniotic sacs. Fraternal twins ALWAYS have separate placentas and sacs but the placentas can grow together and look like one at delivery. So DNA testing is required to know 100 % for sure if the twins are same sex, look alike, and have the same blood type.
Do they do DNA testing at birth for twins now to determine definitely which they are?