This article keeps popping up in my news feeds about a woman pregnant with fraternal boy/girl twins. The boy unfortunately has a hole in his heart and a brain defect, causing him to be but a mere 9ozs while his sister is a robust 2lbs. They don't expect their little guy to make it. They have the sonograms to keep of their little ones and they believe in one of the pictures, the girl is holding her brother's hand.... Now just hear me out... It's a heartbreaking story and I know this gives the family some solace believing the girl is holding the boy... But... Fraternal twins have their own sacs. Only identical twins can share a sac, I would know, being an identical twin myself. Isn't it medically impossible for fraternal twins to be in the same sac? Esp opposite sex twins? So how is this possible for them to be "holding hands"? One sac isn't  very thick but going through 2 sacs to hold onto each other seems kind of unlikely. Again, I think the sentiment is beautiful; the bond between twins is unexplainable. But how could this be at all possible?