Predictive value of presence of amniotic sac without visible embryonic heartbeat in diagnosis of early embryonic demise

Objectives: To assess the diagnostic value and impact on management of visualizing on ultrasound an amniotic sac without a live embryo (amniotic sac sign). We also examined the potential effect on the number of follow-up visits in early pregnancy units of incorporating this sign into current diagnostic algorithms. Methods: This was a prospective cohort study of all pregnant women who attended a single specialist early pregnancy unit from July 2017 to November 2018 with symptoms of pain and/or bleeding, or with a history of ectopic pregnancy or miscarriage, at < 14 weeks' gestation. Detailed initial ultrasound findings were documented, including whether an amniotic sac was present in a normally sited intrauterine pregnancy with absence of a live embryo. Women were followed up until a conclusive diagnosis was made. Results: The study included 6012 women who attended our unit with early pregnancy complications during the study period. A conclusive diagnosis was reached on the initial scan in 4221 (70.2%), whilst 1135 (18.9%) women had a pregnancy of uncertain viability and 656 (10.9%) had a pregnancy of unknown location (PUL). All women with a pregnancy of uncertain viability required follow-up ultrasound scans to differentiate between a live pregnancy and early embryonic demise. An amniotic sac in the absence of a live embryo was found in 174/1135 (15.3%) women with a pregnancy of uncertain viability at the initial ultrasound scan. The diagnosis of early embryonic demise was confirmed in all 134 of these women who attended their follow-up scans. The presence of an amniotic sac without a live embryo at the initial visit had a specificity of 100% (95% CI, 98.53–100.00%) and positive predictive value of 100% (95% CI, 97.2–100.0%) for the diagnosis of early pregnancy failure. A total of 1403/6012 (23.3%) women were asked to attend for a follow-up ultrasound scan to resolve diagnostic uncertainties, including 268/656 (40.9%) women with a PUL. The majority of follow-up scans needed to reach a conclusive diagnosis were in women with a pregnancy of uncertain viability (1135/1403 (80.9%)). By using the presence of the amniotic sac sign to diagnose early pregnancy failure at the first visit, the number of follow-up scans for pregnancies of uncertain viability would be reduced by 14.4%, which accounted for 11% of all follow-up scans during the study period. Conclusions: The finding on ultrasound of an amniotic sac without a live embryo (amniotic sac sign) is a reliable marker of early pregnancy failure and could reduce the number of follow-up scans by 11% in cases of diagnostic uncertainty.