If you have not used assisted reproductive technology and don’t know what type of twins you are having, it is extremely important to determine the type of twins you are carrying early on in your pregnancy.  You should have a consult with a specialist and get an ultrasound preferably by 10-16 weeks gestation.  If you are pregnant with monochorionic twins (sharing one placenta), you need to be aware and educated about Twin to Twin Transfusion Syndrom (TTTS).  The TTTS foundation provides a list of the most important questions for parents at the initial ultrasound (preferably by 10-16 weeks) and questions to ask at weekly ultrasounds.  TTTS is a disease of the placenta that affects identical twins (or higher order multiple) pregnancies.    The TTTS Foundation provides educational, emotional and financial support to families, medical professionals and other care givers before, during and after a diagnosis of twin to twin transfusion syndrome.  Their website explains that the monochorionic placenta contains two anatomic variables that are thought to develop randomly; the first is the presence of blood vessels in the placenta that connect the umbilical cords and circulations of the twins, and the second is the variations in the way the twins share their common placenta.  In some monochorionic twins both of these abnormalities may be present. More