The criteria most often used to diagnose pregnancy failure are the absence of cardiac activity by the time the embryo has reached a certain length (crown–rump length), the absence of a visible embryo by the time the gestational sac has grown to a certain size (mean sac diameter), and the absence of a visible embryo by a certain point in time.
A crown–rump length of 5 mm was widely recommended as a positivity criterion for diagnosing failed pregnancy when no cardiac activity is seen. Recent studies have shown that a 5-6 mm cutoff can result in a false positive diagnosis of pregnancy failure. It is now recommended that we use a 7 mm (rather than 5 mm) cut-off for diagnosing failed pregnancy. Thus if the crown-rump length is 7 mm and there is no heart beat visible, it is suspicious for a failed pregnancy.
It is prudent to use a cutoff of 25 mm (rather than 16 mm) for the mean sac diameter with no visible embryo in diagnosing failed pregnancy (see figure above). This would yield a specificity and positive predictive value of 100% (or as close to 100% as can be determined). When the mean sac diameter is 16 to 24 mm, the lack of an embryo is suspicious for, though not diagnostic of, failed pregnancy
The timing of events in early pregnancy — gestational sac at 5 weeks, yolk sac at 5 ½ weeks, and embryo with heartbeat at 6 weeks — is accurate and reproducible, with a variation of about ± ½ week; this consistency explains the time-related criteria for pregnancy failure. For example, if the initial ultrasonogram shows a gestational sac with a yolk sac and a follow-up scan obtained at least 11 days later does not show an embryo with cardiac activity, the diagnosis of failed pregnancy is established.
According to the Society of Radiologists in Ultrasound Multispecialty Consensus Conference on Early First Trimester Diagnosis of Miscarriage and Exclusion of a Viable Intrauterine Pregnancy, October 2012; the following are guidelines for Transvaginal Ultrasonographic diagnosis of Pregnancy Failure in a Woman with an Intrauterine Pregnancy of Uncertain Viability.
When there are findings suspicious for pregnancy failure, follow-up ultrasonography at 7 to 10 days to assess the pregnancy for viability is generally appropriate. Treatments for early miscarriage are discussed here.
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