Anal dilation during labor

Abstract

Anal dilation during the second stage of labor causes anthropometric changes to the perineum. This ought to be considered when designing anthropometric studies and in studies aiming at minimizing anal sphincter trauma during delivery.

Obstetric anal sphincter injuries: review of anatomical factors and modifiable second stage interventions

“…Table 1 shows the studies involving PL measurements antenatally, and in the first and/or second stage of labour. The average PL is 39 mm (range 37-41 mm) in the late antenatal period or first stage of labour [26][27][28][29][30][31] and PL has increased by 50-60 % at crowning to 60 mm [31][32][33]. Patients with PL ≤25 mm (measured during the first stage) had a significantly greater risk of OASI (40 % vs. 5.6 %, p= 0.004) [26].…”

“…The biomechanics of birth have been studied by clinical observation [33,35,36], MRI studies [39] and stereophotogrammetry [21]. The anal orifice has been found to dilate to 25 mm in the anteroposterior and transverse diameters during crowning, implying a circular dilatation [33].…”

“…The anal orifice has been found to dilate to 25 mm in the anteroposterior and transverse diameters during crowning, implying a circular dilatation [33]. Lien et al [39] found a 2.5-fold to 3-fold increase in different parts of the levator muscle dimensions during birth.…”

Manual perineal protection: The know‐how and the know‐why

“…Based on stereo‐photogrammetric analysis of perineal deformation during fetal head expulsion, MPP seems to produce its protective effect via dispersion of the highest perineal tension over a wider surface area. This is mainly achieved by a reduction in the transverse perineal tension using the accoucheur’s thumb and index finger alongside the vaginal opening . Subsequent computational biomechanical studies showed that such maneuver can produce up to a 30% reduction in relative tension in the perineal region, dependent on the precision of its execution .…”

Classification of episiotomy: towards a standardisation of terminology

“…We agree that the perineal body length and the type of episiotomy are two independent obstetric variables. This was already addressed in one of our recent studies 2 . However, our article in BJOG aimed to draw attention to a careful description of the types of episiotomy described in scientific articles, and proposed a clear classification of the different types 3 .…”