Managing early pregnancy loss: Diagnosing miscarriage is not as easy at you might think

From a patient's perspective if there is one decision a women would expect clinicians to get right with absolute certainty, it would be whether their baby is alive or not. Our current knowledge is such that mistakes will be made. This is evidenced by the recent report from the Irish Health service executive. Until recently the RCOG guidelines on making a diagnosis of miscarriage implied that a pregnancy with an empty gestational sac, visualized using transvaginal ultrasound, with a mean gestational sac diameter (MSD) of ≥20 mm or an embryo with a crown-rump length (CRL) ≥6 mm and no fetal heartbeat may be classified as a miscarriage. No advice was given regarding criteria that should be used on any repeat scan to define miscarriage. Recently a series of papers cast significant doubt on the safety of such guidance. A systematic review of the evidence in the previous literature concluded that the evidence base that has been used to derive the miscarriage guidelines was based on insufficient data, poor quality studies and so cannot be relied upon. New data on MSD and CRL cut-off values showed that those currently in use to define miscarriage were associated with a clinically significant risk of a false positive diagnosis. Furthermore, findings from a multicentre observational study indicate that there can be little or no growth in MSD over at least a week in viable pregnancies. Other authors have emphasized that measurements of these ultrasound parameters may be subject to significant error.

These observations led to the RCOG publishing new interim guidance with immediate effect from October 2011. These advice caution when making a diagnosis of miscarriage pending more definitive data becoming available and make the following recommendations for practice.