Current ultrasound guidelines for detection of miscarriage may lead to wrong diagnosis

Oct 14 2011

Current guidelines that help clinicians decide whether a woman has had a miscarriage are inadequate and not reliable, and following them may lead to the inadvertent termination of wanted pregnancies. This is the conclusion of a series of papers published in the international journal Ultrasound in Obstetrics and Gynecology. "This research shows that the current guidance on how to use ultrasound scans to detect a miscarriage may lead to a wrong diagnosis in some cases. Health professionals need clearer evidence-based guidance to prevent this happening," says Professor BaskyThilaganathan, Editor-in-Chief of the journal.

A miscarriage is often confirmed by using an ultrasound scan to see whether there is any sign of a pregnancy sac or embryo in the womb, and women understandably expect that when a diagnosis of miscarriage is made there is no room for error.

In four studies based at Imperial College London, UK, Queen Mary, University of London, UK, and the Katholieke Universiteit Leuven, Belgium, researchers found that current definitions used to diagnose miscarriage could lead to an incorrect diagnosis.

One piece of research showed that the data behind the current guidelines are based on old and unreliable evidence. "The majority of ultrasound standards used for diagnosis of miscarriage are based on limited evidence," says author Dr. Shakila Thangaratinam, who works in the Women's Health Research Unit at Queen Mary, University of London.

When there are suspicions that a woman has had a miscarriage, common practice is to use ultrasound to measure the size of the gestational sac and the embryo. One study shows that in some cases cut-off values to define miscarriage in these circumstances cannot be relied upon.

When there is doubt about the diagnosis of miscarriage, current guidance suggests the pregnancy sac should be re-measured seven to ten days later. If the sac does not grow, it is assumed that a miscarriage has occurred. However, a study led by Professor Tom Bourne from Imperial College London found that perfectly healthy pregnancies may show no measurable growth over this period of time.

"By identifying this problem we hope that guidelines will be reviewed so that inadvertent termination of wanted pregnancies cannot happen. We also hope backing will be given to even larger studies to test new guidelines prospectively," says Bourne. "Currently there is a risk that some women seeking reassurance with pain or bleeding in early pregnancy may be told they have had a miscarriage, and choose to undergo surgical or medical treatment when the pregnancy is in fact healthy."

The final study revealed that there is up to a 20% variation in the size of gestational sacs reported when different clinicians measure the same pregnancies. If the first measurement over-estimated the sac size and the second measurement some days later underestimated it, then it would be easy to incorrectly conclude that no growth had occurred. "These errors could lead to a false diagnosis of miscarriage being made in some women," says a co-author of this study, Dr. Anne Pexsters of the Katholieke Universiteit Leuven.

"Many of us in clinical practice have been concerned for some time about possible errors relating to the diagnosis of miscarriage. We are pleased that our data have identified where these errors might occur so that we can prevent mistakes happening in the future," says Professor Dirk Timmerman from Katholieke Universiteit Leuven and co-author of three of the research papers.

Almost 20 years ago a landmark enquiry based in Cardiff, UK, drew attention to the fact that early pregnancies can be inappropriately classified as a miscarriage. The authors of the newly published papers believe their data show how to define miscarriage more carefully, with the emphasis being placed on only intervening when there is no doubt about the diagnosis of miscarriage.

"For most women sadly there is nothing we can do to prevent a miscarriage, but we do need to make sure we don't make things worse by intervening unnecessarily in on-going pregnancies. We hope our work means that the guidelines to define miscarriage are made as watertight as we would expect for defining death at any other stage of life," says Professor Bourne.