The Separation Sign

Allwood R.X., Self A., Collins S.L. Separation sign: novel ultrasound sign for ruling out diagnosis of placenta accreta spectrum. Ultrasound Obstet Gynecol. 2022;60(3):390-5.

(Open access paper)

Abstract of Allwood et al


To assess the specificity of the ‘separation sign’ as a predictor of normal placental separation and assess the sensitivity and specificity in women at risk for placenta accreta spectrum (PAS) (placenta praevia or anterior low-lying placenta and ≥1 previous caesarean delivery).


The separation sign was prospectively sought in 194 women at risk of PAS between 22- and 38-weeks’ gestation. The sign detects different elasticity between myometrium and placenta, by looking for different rates of rebound when the utero-placental interface is bounced with the probe. When the sign is positive the placenta appears to move relative to the myometrium and the clear zone is emphasized. Placental separation was assessed at delivery and the separation sign as a predictor for spontaneous separation was assessed.


Of the 194 women, 163 women had a positive separation sign, and 100% of these went on to have normal placental separation at delivery. Of the 24 women with a negative separation sign, 3 (12.5%) had normal placental separation, and 21 (87.5%) were diagnosed with PAS. This generates a sensitivity of 98.19% [94.8%, 99.6%] and specificity of 100% [83.9%, 100.0%]. In the highest-risk cohort (n=35), a positive separation sign remained a confident predictor of normal placental separation with positive predictive value of 100%, with 90.0% [68.3%, 98.8%] sensitivity and 100% [80.5%, 100.0%] specificity.


The separation sign could be used for women considered at risk for PAS, to improve the specificity of prediction of normal placental separation. This could prevent over-treatment with the associated iatrogenic morbidity and unnecessary allocation of clinical resources.