Pregnancy of uncertain viability

Pregnancy of uncertain viability (PUV) is a term given to an intrauterine pregnancy in a situation where there are not enough criteria (usually on ultrasound grounds) to confidently categorize an intrauterine pregnancy as either viable or a failed pregnancy. 

Radiographic features

Ultrasound

Various authors have put forward definitions for a pregnancy to be categorized under this group (please refer to your local protocol/guidelines). Endovaginal/transvaginal ultrasound will show ^1-3:

• intrauterine gestational sac containing an embryo with crown-rump length (CRL) <7 mm with no fetal cardiac activity

• gestational sac with mean sac diameter (MSD) <25 mm containing no embryo

Treatment and prognosis 

It is important that pregnancy failure is confirmed with absolute certainty, and therefore in situations where it is thought highly likely, but does not meet the established criteria, repeat imaging should be recommended.

Recommendations for the most appropriate timeframe of follow-up, and for the diagnostic criteria at followup of a pregnancy of uncertain viability are evolving. In a British Medical Journal publication ⁴, the authors suggest the following:

• if MSD <12 mm with no embryo

  • rescan in 14 days

  • if MSD has not doubled and there is still no embryo - diagnosis of failed pregnancy can be made

• if MSD 12-25 mm with no embryo

  • rescan in 7 days

  • if no embryo with cardiac activity present - diagnosis of failed pregnancy can be made

• if CRL <7 mm with no heart beat

  • rescan in 7 days

  • if still no heartbeat with any size CRL - diagnosis of failed pregnancy can be made

Practical points

Although radiologists commonly use "viable" loosely in the first trimester to mean "living," in some settings, the term "viability" has a specific legal definition (see: failed pregnancy).

See also

• pregnancy of unknown location