OP09.06: Miscarriage: what the scan measures; the patient 'sees' and histology finds

A fetal pole is a collection of pixels measuring mms. Practitioners and patients invest this with an image of the baby to be. We examined whether early pregnancy anatomy measured on scan predicts whether histology found fetal parts. This is important where disposal of pregnancy remains options depend on this. Retrospective observational review of electronic Ultrasound and Results Databases in a tertiary referral Early Pregnancy Unit. Scan details of all patients with a confirmed diagnosis of first trimester missed miscarriage were compared with histology findings, where available, from July 2005-October 2023. 10,333 scans diagnosed missed miscarriage, representing 8943 pregnancies. Histology was available on 4739 pregnancies. We excluded any where the histology “Clinical Details” or report was “incomplete miscarriage”, “RPOC” or “Molar disease”, leaving 3373. We only analysed pregnancies with histology within 14 days of scan – 3155. A CRL was measurable in 2329/3155 (73.8%) pregnancies. The median CRL was 10mm (range:1.1-90.5). Median time between scan and histology was 3 (Range: 0-11) days. Fetal remains were found in 327/3155 (10.4%) pregnancies; 312/2329 (13.4%) with CRL, 15/826 (1.8%) without CRL. A measurable CRL on scan was associated with identification of fetal parts at histology [p < 0.001, χ2 test, Sensitivity: 95.4 (95% CI: 92.8-97.3)%, Specificity: 28.7 (27.0-30.4)%, PPV: 13.4 (12.1-14.8)%, NPV: 98.2 (97.1-99.0)%]. The Odds Ratio of finding fetal remains if a CRL was measured was 8.4 (95% CI: 5.0-14.1). The presence of a CRL was independently associated with finding fetal remains but not the mean GSD or time between scan and histology [p < 0.001, p = 0.28, p = 0.46 respectively, Stepwise Logistic Regression]. Even when a measurable CRL is found on scan, fetal parts are found less commonly than expected. Further analysis will establish a cut off CRL where this is most likely. Our findings challenge perceptions of scan interpretation and should inform patient counselling to manage expectations.