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To better balance the use of ultrasound and the time needed to ensure that an early pregnancy is not incorrectly declared nonviable, a group of experts have introduced new diagnostic thresholds.
New criteria for ultrasonographic determination of when a first-trimester pregnancy is nonviable have been introduced by a group of 15 medical experts from radiology, ob-gyn, and emergency medicine. Convened by the Society of Radiologists in Ultrasound, the group has recommended new diagnostic thresholds that aim to avoid the possibility of physicians causing inadvertent harm by declaring a potentially normal pregnancy nonviable.
“When a doctor tells a woman that her pregnancy has no chance of proceeding, he or she should be absolutely certain of being correct. Our recommendations are based on the latest medical knowledge with input from a variety of medical specialties. We urge providers to familiarize themselves with these recommendations and factor them into their clinical decision-making,” said lead author Peter M. Doubilet, MD, PhD, of Brigham and Women’s Hospital and Harvard Medical School in Boston.
The panel cautions physicians against taking any action that could damage an intrauterine pregnancy based on the results of a single blood test if the ultrasound findings are inconclusive and the woman is in stable condition. Among other key recommendations, the expert panel proposes the following changes:
- Before a pregnancy is considered nonviable, an embryo should measure at least 7 millimeters and be without a heartbeat. Previous standards were that an embryo should measure at least 5 millimeters without a heartbeat.
- When nonviability is based on the size of the gestational sac without an embryo, the new standard should be 25 millimeters, up from 16 millimeters.
- The “discriminatory level” of the pregnancy blood test should no longer be considered reliable for the exclusion of a viable pregnancy.
“With improvement in ultrasound technology, we are able to detect and visualize pregnancies at a very early age. These guidelines represent a consensus that will balance the use of ultrasound and the time needed to ensure that an early pregnancy is not falsely diagnosed as nonviable. There should be no rush to diagnose a miscarriage; more time and more information will improve accuracy and hopefully eliminate misdiagnosis,” said Kurt T. Barnhart, MD, MSCE, a panel member and an ob-gyn at the Perelman School of Medicine at the University of Pennsylvania.
According to Michael Blaivas, MD, another panel member and an emergency medicine physician affiliated with the University of South Carolina, “These are critical guidelines and will help all physicians involved in the care of the emergency patient. They represent an up-to-date and accurate scientific compass for navigating the pathway between opposing forces felt by the emergency physician and his/her consultants who are concerned about the potential morbidity and mortality of an untreated ectopic pregnancy in a patient who may be lost to follow-up, but yet must ensure the safety of an unrecognized early normal pregnancy.”
- Nonviability should not be declared unless the embryo measures at least 7 millimeters and is without a heartbeat.
- When nonviability is based on the size of the gestational sac without an embryo, the new standard should be 25 millimeters.
- Blood tests alone are no longer sufficient to rule out fetal viability.
Doubilet PM, Benson CB, Bourne T, Blaivas M. Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med. 2013;369:1443-1451.