The monochorionic twin placenta in vivo is not a black box.
Machin
G A
GA
D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging*; D006801:Humans; D010920:Placenta / Q000473:pathology; D011247:Pregnancy; D014427:Twins; D016216:Ultrasonography, Prenatal