Re A (conjoined twins) indicated that Gracie was the stronger sibling who was sustaining the life of Rosie. Rosie had only survived birth due to a shared common artery that enabled her sister Gracie to oxygenate blood for both twins. If surgically separated, Gracie had a 94% survival rate, but Rosie was guaranteed to die. However, if they were left conjoined, then Gracie's health—which was already rapidly deteriorating—was predicted to fail before they were six months old. Gracie's death would inevitably result in Rosie's. At first instance, Mr Justice Johnson was left to decide the case without any direct precedents to guide him but
Monochorionic twins Monochorionic twins Monochorionic twins are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins (see multiple birth), these are monochorionic multiples. Monochorionic twins occur in 0.3% of all pregnancies. 75% of monozygotic twin pregnancies are monochorionic; the remaining 25% are "dichorionic diamniotic". If the placenta divides, this takes place after the third day after fertilization. Monochorionic twins generally have two amniotic sacs (called Monochorionic-Diamniotic "MoDi"), but sometimes, in the case of monoamniotic twins (Monochorionic-Monoamniotic "MoMo"), they also share the same amniotic sac. Monoamniotic twins occur when the split takes place after