Dr. Lindemann opines, “There are different types of twin gestations based on the number of placentas and the existence of membranes between the twins. Without a separating membrane, the twins have problems getting their umbilical cords twisted. There are often discrepancies in size with one twin growing larger than the other twin, probably because it gets more nutrition.”
“However, most twins contain a membrane between babies so that cords can’t get mixed up and they have their own nutrition. When this happens, twins have a reasonable chance of growing normally and being born relatively at term, for example at 39 weeks.”