How can a SNP-based test performed as early as 9 weeks help reduce the risk of potential complications of twin-to-twin transfusion syndrome? In what way is ultrasound less accurate than NIPT in diagnosing monochorionicity in a twin pregnancy and its associated complications?

How can a SNP-based test performed as early as 9 weeks help reduce the risk of potential complications of twin-to-twin transfusion syndrome? In what way is ultrasound less accurate than NIPT in diagnosing monochorionicity in a twin pregnancy and its associated complications?