[1] In a normal pregnancy, an embryo would be visible on an ultrasound by six weeks after the woman's last menstrual period.

[2] It likely occurs as a result of early embryonic death with continued development of the trophoblast.

[3] For diagnosis, the sac must be of sufficient size that the absence of normal embryonic elements is established.

[8] Generally, a transvaginal ultrasound is used to investigate a suspected case of blighted ovum.

[9] A transabdominal ultrasound can be used to diagnose anembryonic pregnancy if a gestational sac can be identified, but is empty.