To say twin discordance the difference in the two twin's weight should be:
Discordant twins: The donor twin should be > 20% smaller in weight than the recipient twin Abdominal circumference difference of >15%
15% with the larger twin as index
15% with the smaller twin as index
20% with the larger twin as index
25% with the smaller twin as index
Twin Pregnancy, Molar Pregnancy, Gestational Trophoblastic disease and contraception in special situations (Sour Grapes!)