Diagnosis guidelines may be inadequate to help clinicians detect viable pregnancies thought to be miscarriages

Studies suggest that guidance could lead to a wrong diagnosis of miscarriage in some cases, during early pregnancy - News

Adapted from a news release issued by Wiley-Blackwell
Friday 14 October

Current guidelines that help clinicians decide whether a woman has had a miscarriage are unreliable, possibly resulting in the inadvertent termination of wanted pregnancies, according to new research.

The findings from three new studies at Imperial College London and Katholieke Universiteit Leuven show that a viable embryo may be present in some cases in which a miscarriage has been diagnosed during early pregnancy. The research is published in the journal Ultrasound in Obstetrics and Gynecology.

When a woman is suspected of having a miscarriage in the first trimester, common practice is to use ultrasound to measure the size of the gestational sac. If the sac is above a predefined size and no embryo is seen, a miscarriage is diagnosed and the woman may choose to have the pregnancy terminated. The first study shows that in some cases, cut-off values to define miscarriage in these circumstances cannot be relied upon.

Furthermore, if there is doubt about the diagnosis, current guidance suggests that the sac should be re-measured 7 to 10 days later. If the sac does not grow, it is assumed that a miscarriage has occurred. However, the group at Imperial, led by Professor Tom Bourne from the Department of Surgery and Cancer, also found that 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," said Professor Bourne. "We also hope backing will be given to even larger studies to test new guidelines prospectively.

"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."

A third study, also by the researchers at Imperial and KU Leuven, revealed that there is up to a 20 per cent variation in the size of gestational sacs reported when different clinicians measure the same pregnancies. As a result it might be easy to incorrectly conclude that an empty gestation sac is above the cut-off in size used to define a miscarriage or that no growth had occurred when a scan is repeated.

Professor Dirk Timmerman, head of benign gynecology at Leuven and co-author of three of the research papers, said: "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."

One piece of research published today 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," said author Dr. Shakila Thangaratinam, from the Women’s Health Research Unit at Queen Mary, University of London.

The researchers cannot be certain about the numbers or proportion of women who might be affected by misdiagnosis, because there is a lack of firm data about the numbers of miscarriages in any given year and about the proportion of women whose scans are of the type that the researchers have identified as having the potential to be misdiagnosed.

Almost 20 years ago a landmark enquiry from the University of Cardiff 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," said Professor Bourne.

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Study references:

"Accuracy of first-trimester ultrasound in the diagnosis of early embryonic demise: a systematic review." Jeve Y, Rana R, Bhide A, Thangaratinam S. Ultrasound Obstet Gynecol 2011; DOI: 10.1002/uog.10108

"Limitations of current definitions of miscarriage using mean gestational sac diameter and crown–rump length measurements: a multicenter observational study". Abdallah Y, Daemen A, Kirk E, Pexsters A, Naji O, Stalder C, Gould D, Ahmed S, Guha S, Syed S, Bottomley C, Timmerman, Bourne T. Ultrasound Obstet Gynecol 2011; DOI: 10.1002/uog.10109

"Gestational sac and embryonic growth are not useful as criteria to define miscarriage: a multicenter observational study". Abdallah Y, Daemen A, Guha S, Syed S, Naji O, Pexsters A, Kirk E, Stalder C, Gould D, Ahmed S, Bottomley C, Timmerman D, Bourne T. Ultrasound Obstet Gynecol 2011; DOI:10.1002/uog.10075

Clinical implications of intra- and interobserver reproducibility of transvaginal sonographic measurements of gestational sac and crown–rump length at 6–9 weeks’ gestation. Pexsters A, Luts J, van Schoubroeck D, Bottomley C, van Calster B, van Huffel S, Abdallah Y, D’Hooghe T, Lees C, Timmerman D, Bourne T. Ultrasound Obstet Gynecol 2011; DOI: 10.1002/uog.8884