Guidelines for Diagnosing Early Pregnancy Loss Emphasize Reduction in False Positives

By Eva Martin, MD of Elm Tree Medical, Inc.

Early pregnancy is one of the most exciting- and nerve-wracking- times for a new mother. Amidst the joy of expecting a new baby are usually worries about whether the pregnancy is healthy and normal. Early pregnancy loss occurs when there is an intrauterine pregnancy either with no embryo or with an embryo without a heartbeat, before 13 weeks. Early pregnancy loss occurs in 15% of clinically recognized pregnancies. Doctors can use levels of the pregnancy hormone hCG and ultrasound to assist in this diagnosis. But how certain is the diagnosis of a healthy versus nonviable early pregnancy? How can we be sure that we do not misdiagnose a viable pregnancy as an early pregnancy loss and intervene inappropriately? Read on to learn about the new ultrasound guidelines meant to increase certainty in diagnosing early pregnancy loss.

Former recommendations for diagnosis of an early pregnancy loss led to some false-positives. In other words, the thresholds were such that viable pregnancies would be misdiagnosed as nonviable and could potentially lead to interventions and treatments that harmed a healthy pregnancy. Previously, the guidelines required an ultrasound Crown-Rump Length of 5mm without a heartbeat or an empty gestational sac of 16mm (sac with no fetus visualized) to diagnose early pregnancy loss. Unfortunately, at 5mm, 8.3% of pregnancies with no cardiac activity visualized on ultrasound are actually viable. At 16mm, 4.4% of pregnancies with no embryo visualized inside the gestational sac are actually viable. 

The new guidelines, issued in May 2015, are stricter than the previous guidelines, to eliminate false positives. The Crown-Rump Length must be 7 mm without visible cardiac activity before a diagnosis of early pregnancy loss can be made. The gestational sac must measure at least 25 mm without a visible embryo before diagnosing an anembryonic pregnancy (also known as a blighted ovum). In prior studies, these thresholds would lead to a 0% false positive rate.

Most importantly, ultrasound findings must be examined in light of the clinical scenario and patient preference. However, these new guidelines emphasize an important point: it is better to wait a little longer and gather serial ultrasounds and more data than to misdiagnose early pregnancy loss and inadvertently harm a healthy pregnancy.

We want to hear from you! Do you find the new guidelines more helpful in making a diagnosis? How has the change impacted your practice?