Thanks for the query.
According to your description it is biamniotic monochorionic twin pregnancy
Usually with progression of the gestation diastolic flow will decrease due to the dilatation of blood vessels and decreased vascular resistance.
But as S/D ratio, resistance index etc are abnormal, it is indicating the possibility of increased vascular resistance which is usually seen in cases of hypertension
So you better get evaluated regarding this and take necessary treatment to prevent complications.