An 8 week pregnant female presented with vaginal bleeding and ruptured cysts of hydatidiform mole. In case of hydatidiform mole, the investigation used for diagnosis is:

Though beta-hCG levels are helpful, the diagnosis of molar pregnancy is more frequently found sonographically because of the identifiable diffuse swelling and enlargement of the chorionic villi. Most first-trimester complete moles demonstrate a typical sonographic appearance: a complex, echogenic, intrauterine mass containing many small cystic spaces. Fetal tissues and amnionic sac are absent. In contrast, sonographic features of a paial molar pregnancy include a thickened, hydropic placenta with a concomitant fetus. Ref: Hoffman B.L., Schorge J.O., Schaffer J.I., Halvorson L.M., Bradshaw K.D., Cunningham F.G., Calver L.E. (2012). Chapter 37. Gestational Trophoblastic Disease. In B.L. Hoffman, J.O. Schorge, J.I. Schaffer, L.M. Halvorson, K.D. Bradshaw, F.G. Cunningham, L.E. Calver (Eds), Williams Gynecology, 2e.