The importance of bladder volume in the ultrasound diagnosis of placenta accreta spectrum disorders.

OBJECTIVE: To assess how a quantifiable measure of vascularity-i.e. abnormal confluence (Acon ) in the subplacental myometrium observed by three-dimensional power-Doppler ultrasonography-changes with different bladder volumes.

METHODS: In a prospective observational study, women referred to a tertiary UK center with suspected PAS disorders were recruited between August 2016 and May 2017. The largest area of confluent three-dimensional power-Doppler signal (Acon ) at the uteroplacental interface was estimated under two bladder volumes differing by at least 200 mL.

RESULTS: Acon was calculated for 14 women, of whom seven were subsequently found to have PAS disorders. For these seven women, log(Acon ) was significantly greater when measured with a filled bladder than when measured with an unfilled bladder (P<0.001).

CONCLUSION: Objective evidence was found for a quantifiable difference in vascularity in the myometrium with bladder volume among women with PAS disorders. This difference has sufficient magnitude to influence the potential of Acon as a diagnostic marker.