The doctor isn't seeing a dividing line between the twins. What does that mean?
Some twins learn to share at a very young age. The majority of identical twins will share the same placenta but have separate amniotic sacs (monochorionic diamniotic), although a smaller percentage of identicals have their own of each one (dichorionic diamniotic). When there’s sharing involved, there’s a higher risk of complications, so you’ll likely be getting some extra attention from your doctor, and will almost definitely be referred to a maternal-fetal medicine specialist. One serious potential complication is twin-to-twin transfusion syndrome, where one twin gets too much blood and nutrients while the other doesn’t get enough. It’s still a relatively rare occurrence, but if your twins are sharing a placenta, let’s just say you’ll become very familiar with the magazines in her waiting room.
Plus more from The Bump:
Important questions to ask if having twins.
Are multiple pregnancies riskier than single pregnancies?
Vanishing Twins syndrome.