Normal Values of Anal Sphincter Biometry by 4-Dimensional Translabial Ultrasound: A Retrospective Study of Pregnant Women in Their Third Trimester.

Anal sphincter biometry can be assessed with good repeatability by TLUS. The EAS seems longer ventrally. Asymmetry of the EAS could result in a false-positive diagnosis of defects in women in whom the ventral EAS terminates more caudally than its dorsal aspect, which seems uncommon. Hence, the likelihood of a false-positive diagnosis of substantial defects of the EAS using the published method seems low.