An<unk>  (aka blighted ovum) is a pregnancy in which a visible embryo never develops within a normal-appearing gestational sac, which likely occurs as a result of early embryonic death with continued development of the trophoblast.
When small, the sac cannot be distinguished from the early normal pregnancy, as there may be a yolk sac, though a fetal pole is not seen.
This is one of the causes of miscarriage of a pregnancy.
For diagnosis, the sac must be of sufficient size that the absence of normal embryonic elements is established.
A pregnancy is<unk>  if a transvaginal ultrasound reveals a sac with a mean gestational sac diameter (MGD) greater than 13 mm and no yolk sac, or a MGD >18 mm with no embryo.
Many centers offer mothers a follow-up ultrasound 10 days later to verify diagnosis.
Several management options exist for<unk>  pregnancies which have not miscarried on their own.
Anembryonic gestation
Fetus in fetu
Gestational trophoblastic neoplasia
Unwanted pregnancy
Fetal methotrexate syndrome
Retained products of conception
Prenatal development
Parasitic twin