What is the role of Ultrasound for conjoined twins?
Conjoined twins constitute a rare (about 1 per 200,000 live births in the United States) complication of twinning in which the dividing zygote that would result in separate embryos fails to divide completely.
The chief role of US is to determine the type of conjoined twins, what anatomic structures are shared or connected, and the nature of the vascular anatomy. The precise description of conjoined twins is complex, but a simple designation based on where the fetuses are joined includes: craniopagus (joined at the head), thoracopagus (joined at the thorax), omphalopagus (joined at the abdomen), and ischiopagus (joined at the pelvis). Combinations of these (e.g., thoraco-omphalopagus) can occur. An example of thoraco-omphalopagus conjoined twins.
From US and MRI studies, the fetal therapy team can determine if separation of the fetuses is possible and if such separation can result in a single, or two, live neonate(s). Separation surgery is always postnatal.