First Do No Harm: Guidelines Define a Nonviable Pregnancy

Ricki Lewis, PhD

October 09, 2013

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.

Implementation of new diagnostic thresholds for transvaginal ultrasound and not basing decisions solely on hCG test results may avoid situations such as inappropriate administration of intramuscular methotrexate for a suspected ectopic pregnancy or of evacuating the uterus when the embryo is indeed viable.

Peter M. Doubilet, MD, PhD, from Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, and the other 14 members of the Society of Radiologists in Ultrasound Multispecialty Panel on Early First Trimester Diagnosis of Miscarriage and Exclusion of a Viable Intrauterine Pregnancy evaluated data to establish broader limits for assessing prenatal viability. The panel represents obstetrics and gynecology, radiology, and emergency medicine. Their goal was to attain 100% specificity: no false-positives of nonviability.

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 mm and no heartbeat

  • 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 mm difference between mean sac diameter and crown–rump length."

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.

The researchers also evaluated the role of hCG level at specific points in gestation in diagnosing or ruling out a viable intrauterine pregnancy and in informing patient care decisions. The researchers conclude that considering hCG level alone can be misleading because levels at specific times overlap for viable intrauterine pregnancies, nonviable intrauterine pregnancies, and ectopic pregnancies. Recent evidence shows that hCG levels accepted in the past as indicative of a nonviable pregnancy may not be reliable.

In addition, the authors present diagnostic and management guidelines in cases where the embryo is in an unknown location.

"A false positive diagnosis of nonviable pregnancy early in the first trimester — incorrectly diagnosing pregnancy failure in a woman...— can prompt interventions that damage a pregnancy that might have had a normal outcome," the authors conclude. "Recent research has shown the need to adopt more stringent criteria for the diagnosis of nonviability in order to minimize or avoid false positive test results. The guidelines presented here, if promulgated widely to practitioners in the various specialties involved in the diagnosis and management of problems in early pregnancy, would improve patient care and reduce the risk of inadvertent harm to potentially normal pregnancies."

Full conflict-of-interest information is available on the journal's Web site.

N Engl J Med. 2013;369:1443-1451.

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