A blighted ovum is a pregnancy in which the embryo never develops or develops and is reabsorbed.^[1] In a normal pregnancy, an embryo would be visible on an ultrasound by six weeks after the woman's last menstrual period.^[2] Anembryonic gestation is one of the causes of miscarriage of a pregnancy and accounts for roughly half of first-trimester miscarriages.^[3][4][5][6] A blighted ovum cannot result in a viable pregnancy.^[2][7]

A blighted ovum or anembryonic gestation is characterized by a normal-appearing gestational sac, but the absence of an embryo.^[2] It 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. In anembryonic pregnancy, levels of the pregnancy hormone human chorionic gonadotropin (hCG) typically rise for a time, which can cause positive pregnancy test results and pregnancy symptoms such as tender breasts.^[2][7] Because of the presence of hCG, an ultrasound is typically necessary to diagnose an anembryonic pregnancy.^[3] For diagnosis, the sac must be of sufficient size that the absence of normal embryonic elements is established. The criteria depends on the type of ultrasound exam performed. A transvaginal ultrasound provides a better view of early pregnancy than a transabdominal ultrasound.^[8] Generally, a transvaginal ultrasound is used to investigate a suspected case of blighted ovum.^[2][7] A pregnancy is anembryonic if a transvaginal ultrasound reveals a sac with a mean gestational sac diameter (MGD) greater than 25 mm and no yolk sac, or an MGD >25 mm with no embryo.^[9] A transabdominal ultrasound can be used to diagnose anembryonic pregnancy if a gestational sac can be identified, but is empty.^[3] An anembryonic pregnancy is never viable, as in viable pregnancy the embryo must form with the gestational sac.^[2]

• Ovum
• Products of conception