The term blighted ovum used to describe an impregnated ovum whose development has become arrested at an early gestational stage before completion of the first trimester. Whereas the histopsthologic examination o the abortive tissue does not reveal any recongnizable fetal part. The main histopathologic criteria used for the diagnosis of degeneration ovum were absent or defective vascularity hydropic degeneration of the stroma, large villi and great variation in the size of villi or villous hypoplasia with small and poorly vascularized villi and a hypoplasia trophoblast. The data obtained by this study showed a different distribution of karyotypic abnormalities in echorgraphically defined BO and suggest that genes on chromosomes 16 and 22 may be responsible for the very precocious arrest of embryonic development, leading to the echograhically (blighted ovum) appearance. In this study the yolk sac could be detected in all patients with normal early pregnancy and its growth could be evaluated by the high resolution of transvaginal ultrasound which found that there is a high significant relation between yolk sac size and gestational age. The yolk sac diamater increased from a mean size of 2.3 mm at 5th week of gestation and attained a maximum mean size of 5.1mm at 10th week of gestation then decreased in the size and started to be undetectable.