An expert panel convened by the Society of Radiologists in Ultrasound has issued recommendations for the use of ultrasonography in determining when a first trimester pregnancy is nonviable.

The new criteria, published Oct. 10 in the New England Journal of Medicine, aim to prevent unneeded and damaging interventions into normal pregnancies.

“Research in the past two to three years has shown that previously accepted criteria for ruling out a viable pregnancy, which were based on small numbers of patients, are not stringent enough to avoid false positive test results,” wrote Peter M. Doubilet, MD, PhD, of Brigham and Women's Hospital and Harvard Medical School in Boston, and colleagues.

Key points made by the 15-member panel include:

• Pregnancies should now be diagnosed as nonviable if ultrasound shows an embryo measuring at least seven millimeters without a heartbeat. Previous guidelines considered five millimeter embryos without a heartbeat nonviable.
• The threshold for nonviability based on the size of the gestational sac without an embryo should be raised from 16 to 25 millimeters.
• The “discriminatory level” of the pregnancy blood test is not reliable for excluding a viable pregnancy.
• Physicians should be cautioned against taking action that could damage an intrauterine pregnancy based on a single blood test if the woman is in stable condition and the ultrasound findings are inconclusive.

“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,” wrote the authors.

The multispecialty panel that made the recommendations consisted of experts from radiology, obstetrics-gynecology and emergency medicine.