Twins are fraternal if they are produced by 2 sperms and 2 different egg cells and they have a different yolk sacs and placenta . Identical twins share the same yolk sac, placenta, and amniotic membrane(you could prob just see one bag if its identical).
Btw, congratulations on your pregnancy hun and it must be really exciting to carry twins :)
good luck and hope you have a smooth pregnancy throughout.
Love
~anna~