First Do No Harm: Guidelines Define a Nonviable Pregnancy

New criteria for the use of ultrasonography to assess prenatal viability, introduced by the Society of Radiologists in Ultrasound, will help ensure obstetricians are not too hasty in determining that an embryo has ceased developing. The guidelines were published as a review article in the October 10 issue of the New England Journal of Medicine.
Detection of serum human chorionic gonadotropin (hCG) concentration and transvaginal ultrasound imaging have enabled ever-earlier detection of pregnancy. However, previous guidelines may allow false-positives, designating an embryo as absent or nonviable when waiting a few days and repeating tests may reveal that it is neither.
The new, more stringent, diagnostic criteria are:

• "Crown–rump length of ≥7 mm and no heartbeat
• Mean sac diameter of ≥25 mm and no embryo
• Absence of embryo with heartbeat ≥2 [weeks] after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat ≥11 days after a scan that showed a gestational sac with a yolk sac."

The report also lists 8 findings that are "suspicious for, but not diagnostic of, pregnancy failure":

• "Crown–rump length of <7 ad="" beat="" heart="" mm="" no="">
• Mean sac diameter of 16–24 mm and no embryo
• Absence of embryo with heartbeat 7–13 days after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat 7–10 days after a scan that showed a gestational sac with a yolk sac
• Absence of embryo ≥6 wk after last menstrual period
• Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo)
• Enlarged yolk sac (>7 mm)
• Small gestational sac in relation to the size of the embryo (<5 and="" between="" crown="" diameter="" difference="" length.="" mean="" mm="" rump="" sac="">

If a physician sees 1 or more of these findings, they should investigate further but not immediately reach the conclusion that the pregnancy is not viable, the authors say. "Because none of these signs have been extensively studied, they are considered to be suspicious for, though not diagnostic of, failed pregnancy," the authors write.(N Engl J Med. 2013;369:1443-1451.)