An anembryonic gestation (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.
More on [ Anembryonic gestation ]

Blighted Ovum on Baby Center - Informative article regarding common blighted ova questions including what to expect and future conception. Also includes an informative Reader's Comments section.
Blighted Ovum: American Pregnancy Association - Provides insight into causes, symptoms, and discusses having a DC or not; offers a toll-free education support line.
Meta Description: [ A blighted ovum type of pregnancy loss is explained and how to recognize signs of a blighted ovum. ]
Conception, But No Fetus (Blighted Ovum) - Questions and answers regarding this diagnosis.
Meta Description: [ Conception, But No Fetus (Blighted Ovum) ]
Coping with Pregnancy Loss - Information regarding the diagnosis of a blighted ovum, personal stories, and statistical chances of additional loss.
Meta Description: [ Pregnancy loss/miscarriage ]
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Health Encyclopedia - Blighted Ovum - Contains information understanding the diagnosis of a blighted ovum as well as highlights the risks, long-term effects and possible prevention of future blighted ova.
Medcyclopaedia - Blighted Ovum - Standard definition of a blighted ovum (anembryonic gestation)
Meta Description: [ Home, library, topics, volume iv 2, b, blighted ovum ]
The Misdiagnosed Miscarriage - Dedicated to understanding the diagnosis and possible misdiagnosis of a blighted ovum includes stories of actual miscarriages and misdiagnosed miscarriages.
Meta Description: [ Providing support for women who may or may not be miscarrying. ]