OC15.04: A prospective multi‐centre evaluation of the predictive value of the ‘amniotic sac sign’ in the diagnosis of early miscarriage

A large single-centre study showed that the presence of an amniotic sac without a live embryo with a CRL <7mm on ultrasound scan was accurate in the detection of miscarriage at the initial visit. Our aim was to externally validate this ‘amniotic sac sign’ by reassessing its specificity for the diagnosis of miscarriage and assessing the potential reduction in follow-up visits for pregnancies of uncertain viability (PUV). This was a prospective multi-centre cohort study of pregnant women less than 14 weeks gestation, who attended an early pregnancy unit between January and August 2023. Outcomes included diagnosis by the first trimester dating scan, number of follow-up visits and misdiagnosis of the ‘amniotic sac sign’. Our study population included 1897 pregnancies from 1890 women over 5 centres. A conclusive diagnosis was reached on initial scan in 1122 (59.1%) of cases. There were 266 (14%) PUL and 509 (26.8%) PUV. 420/509 (82.5%) PUV had follow-up totalling 528 scans to reach a final diagnosis. 174 (42.4%) had live pregnancies, 223 (52.4%) had a miscarriage, 22 (5%) had a termination and 1 (0.2%) had an ectopic pregnancy. 41/420 (10%) PUV had an amniotic sac without a live embryo with CRL <7mm. The ‘amniotic sac sign’ had a sensitivity of 18.4% (95%CI 13.5 to 24.1%), specificity of 100% (95%CI 98.1 to 100%), PPV of 100% (95%CI 91.4 to 100%), NPV of 52.91% (95%CI 50.4 to 54.5%) and accuracy of 56.7% (95%CI 51.8 to 61.5%) for the detection of miscarriage. By using the amniotic sac sign at the initial visit, the number of women with PUV needing follow-up could be reduced by 10% (41/420) and the number of scans by 9% (47/528). Our multi-centre study has shown that the presence of an amniotic sac without a live embryo has 100% specificity for the diagnosis of miscarriage and can be reproduced by other units. Application of this sign could reduce follow-up of PUV by 10% reducing patient anxiety and providing financial benefits.