Anembryonic pregnancy

An anembryonic pregnancy (sometimes termed a blighted ovum) is a gestational sac which develops without a fetal pole. Some authors suggest the term blighted ovum should be avoided as histologically fetal material can be demonstrated in most cases.

Clinical presentation

The patient may be asymptomatic, presenting for early pregnancy ultrasound. Alternatively, she may present with vaginal bleeding in early pregnancy.

Radiographic features

Ultrasound

An anembryonic pregnancy may be diagnosed when there is no fetal pole identified on trans-vaginal scanning ⁴, and:

• the size of the gestational sac is such that a fetal pole should be seen : MSD ≥ 25 mm (by RCOG criteria)

• there is little or no growth of the gestational sac between interval scans
  • normally the MSD should increase by 1 mm per day
  • if MSD is too small to ascertain viability on the initial ultrasound, a follow up scan in 10-14 days should differentiate early pregnancy from a failed pregnancy (see: pregnancy of uncertain viability)

Other ancillary features include

• absent yolk sac when MSD > 8 mm
• poor decidual reaction : often < 2 mm
• irregular gestational sac shape 
• abnormally low sac position

Differential diagnosis

Differential diagnosis for an empty gestational sac includes

• early pregnancy (intra-uterine) 
• pseudogestational sac
• gestational trophoblastic disease : especially 1^st trimester molar pregnancies ⁵

See also

• fetal demise
• miscarriage
  • threatened miscarriage
  • missed miscarriage
  • inevitable miscarriage
  • incomplete miscarriage
  • complete miscarriage - spontaneous miscarriage
  • habitual miscarriage