Miscarriage Ultrasound Diagnosis May Still Need Rescan

Troy Brown, RN

September 25, 2015

Current guidelines regarding ultrasonographic diagnosis of miscarriage may still be associated with misdiagnoses and should be updated to reflect new evidence, according to a prospective, multicenter, observational trial.

"Guidance on timing between scans and expected findings on repeat scans are still too liberal," the authors write. "Protocols for miscarriage diagnosis should be reviewed to account for this evidence to avoid misdiagnosis of miscarriage and the risk of terminating viable pregnancies."

Tom Bourne, MD, PhD, consultant gynecologist and professor, Queen Charlotte's and Chelsea Hospital, Imperial College London, United Kingdom, and colleagues report their findings in an article published September 23 in BMJ.

The study's primary objective was to validate recent guidance changes regarding ultrasonographic diagnosis of miscarriage. These guidelines use measurements of embryo crown–rump length (CRL) and mean gestational sac diameter (MSD); the cut-off values were changed in 2011, but the data supporting the change had wide confidence intervals.

Secondary objectives were to study the influence of gestational age on interpretation of MSD and CRL values, determine the optimal intervals between scans, and identify the findings on repeat scans that definitively diagnose miscarriage.

Current guidelines address when to repeat scans when viability is uncertain on an initial scan and how to interpret findings, but this is not evidence-based. In addition, there is no guidance on how to relate gestational age to scan findings and a possible diagnosis of miscarriage.

The study's final outcome was pregnancy viability at 11 to 14 weeks' gestation.

The study took place at seven hospital-based early pregnancy assessment units in the United Kingdom. The researchers included 2845 women with intrauterine pregnancies of unknown viability if transvaginal ultrasonography found an intrauterine pregnancy of uncertain viability. The women were recruited in two waves, between September 2010 and March 2011 and between August 2011 and May 2013.

In three hospitals, researchers initially defined "an intrauterine pregnancy of uncertain viability" as an empty gestational sac smaller than 20 mm mean diameter with or without a visible yolk sac but without embryo, or an embryo with a CRL smaller than 6 mm with no heartbeat. After the guidance was amended in December 2011, the researchers changed the definition to an MSD less than 25 mm or embryo CRL smaller than 7 mm. Researchers at one unit extended the definition throughout to include an MSD smaller than 30 mm or embryo CRL less than 8 mm.

The investigators found that an initial scan showing an empty gestational sac of mean diameter 25 mm or larger had 100% specificity for miscarriage, as did an embryo with no heart activity and a CRL of 7 mm or larger.

After 70 days' gestation, an empty gestational sac of mean diameter 18 mm or larger had 100% specificity for miscarriage, as did an embryo with a CRL of 3 mm or larger with no heart activity.

For repeat scans, a pregnancy with an embryo without heart activity on initial scan and a repeat scan 7 or more days later had 100% specificity for miscarriage, as did a pregnancy with no embryo and an MSD smaller than 12 mm if the sac size had not doubled after 14 or more days, and pregnancies with no embryo and an MSD 12 mm or larger with no embryo heart activity after 7 or more days.

"Despite ultrasound technology, we cannot get around the fact that often we still must resort to watching and waiting," Elizabeth Anne McCarthy, MB BS, senior lecturer, and Stephen Tong, MB BS PhD, professor, University of Melbourne, Department of Obstetrics and Gynaecology at Mercy Hospital for Women, Heidelberg, Victoria, Australia, write in a linked editorial.

"In the era of in vitro fertilisation and home pregnancy tests, many women present early for their first ultrasound examination," they write. "Thus it is common at a viability ultrasound investigation that embryonic and gestational sac sizes are too small to be certain whether an early pregnancy is still viable or a miscarriage has occurred." For this reason, women are often told to return a week or 2 later for a repeat ultrasound to determine whether structures have grown.

This study "is an important advance that provides greater certainty," the editorialists conclude.

"There are lots of other clues...that can be used in the diagnosis of miscarriage, but the goals of the authors are to focus on radiological data alone, and to limit the false positives," Jeff Ecker, MD, chair, Obstetrics Committee, American College of Obstetrics and Gynecology, told Medscape Medical News.

"In my institution, we've already adopted those recommendations, but [the study] may help make others aware, or give emphasis to those criteria," Dr Ecker added.

The authors, editorialists, and Dr Ecker have disclosed no relevant financial relationships.

BMJ. 2015;351:h4579. Article full text, Editorial full text

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