Perineal body and anal sphincter biometrics and stiffness using elastography during labor: a feasibility study

The study aimed to evaluate the biometrics and stiffness of the perineal body and anal sphincter using 2D-mode ultrasound and shear wave elastography (SWE) during labor and to assess their association with perineal tears.

A prospective observational study was conducted on pregnant women. The perineal body (PB), the external anal sphincter (EAS), the internal anal sphincter (IAS) and the anal mucosa (AM) biometrics and stiffness were measured during labor using a transperineal 2D-mode ultrasound and shear wave elastography (SWE), respectively, at rest and during Valsalva maneuvers.

Among the 10 women who underwent a vaginal delivery, 6 (60.0 %) perineal tears occurred. All were first degree perineal tears. Before expulsive efforts, the PB area at rest was statistically higher in women with perineal tears (1.0 ± 0.1 cm2 vs 0.3 ± 0.1 cm2, p < 0.01). The perineal body length, height and area seemed to decrease between the onset of labor and the beginning of expulsive efforts. The PB Youngs' modulus at rest at the onset of labor or before expulsive efforts were 11.9 ± 3.6 kPa and 25.7 ± 18.9 kPa, respectively. The PB elastic modulus at rest and at the onset of labor (11.3 ± 4.1 vs 12.9 ± 2.9 kPa, p = 0.6) or before expulsive efforts (18.0 ± 15.9 vs 37.4 ± 18.6 kPa, p = 0.1) tended to be higher in women with a perineal tear at delivery, but it was not statistically significant.

In vivo assessment of both the perineal body and anal sphincter biometrics and stiffness during labor in women is feasible. The perineal body area during labor could be a predictive factor for perineal tears, suggesting a potential link between its stiffness and tear risk.

The study was registered on https://clinicaltrials.gov (NCT05556304): https://classic.

gov/ct2/show/NCT05556304.