This week an important series of papers have been published in the peer reviewed International Journal Ultrasound in Obstetrics and Gynecology. These papers cast significant doubt on the current guidelines being used to diagnose miscarriage both in the UK and elsewhere in the world.
A systematic review of the evidence in the literature (not including new the new data from Imperial college) concludes that the evidence base that has been used to derive the current miscarriage guidelines is based on insufficient data, poor quality studies and so cannot be relied upon in all cases. This view is supported by an opinion paper by Professor Tom Bourne that highlights the problem further and again illustrates that the cut-off values for gestation sac and embryo size may lead to a viable pregnancy being wrongly diagnosed as a miscarriage.
Three papers are also published by the London-Leuven research group based at Imperial College London and the Katholieke University in Leuven, Belgium. These represent the largest study published on the ultrasound based diagnosis of early miscarriage and include over a one thousand women.
The findings of these papers can be summarized into four important points:
1. The current UK guideline used to define miscarriage states an empty gestation sac with mean sac diameter (MSD) of over 20 mm can be classified as miscarriage. The study shows this is associated with a 0.5% risk of misclassifying a viable pregnancy as a miscarriage. The confidence intervals show that at worst the false positive rate at this cut-off could be as high as 3.0%.
2. For an MSD cutoff of 16 mm as used in the USA, the false positive rate for miscarriage is 4.4% and may be as high as 8.4%.
3. Current guidance that an absence of MSD growth may be a sign of miscarriage. The published studies show that this is not the case and that there may be little or absent growth over several days and still a pregnancy can be viable. So an absence of growth in either an embryo or gestation sac is not a definitive sign of miscarriage.
4. There is variation in how different clinicians will measure any given gestation sac or embryo. This is important as it may mean that an MSD measurement of 20 mm may in fact be 16 mm – leading to a higher risk of the pregnancy being misdiagnosed as a miscarriage.
5. The number of pregnancies this may have been affected by this or might be relevant to in the future is not accurately known.
It is very important to put these papers in context for both clinicians and patients. What these papers DO NOT say is that the diagnosis of miscarriage for the vast majority of women who have had or will have a miscarriage is likely to be incorrect. These papers relate to the specific situation where a women undergoes an ultrasound scan and a gestations sac is visualized, but no embryo with a heartbeat is seen. Furthermore they apply to relatively small gestation sacs of under 25 mm. The papers do not suggest there is any problem when a diagnosis of miscarriage is made in the presence of either gestations sacs with an MSD of greater than 25 mm or embryos that are more than 7 mm in size.
However these data are important and show that current criteria for the use of ultrasound to diagnose miscarriage cannot exclude the possibility of misdiagnosis. The authors suggest that the guidance be changed on the basis of this new information in order to avoid the possibility of error.
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. http://doi.wiley.com/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: http://doi.wiley.com/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: http://doi.wiley.com/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: http://doi.wiley.com/10.1002/uog.8884