Dynamic External Pelvimetry Test in Third Trimester Pregnant Women: Shifting Positions Affect Pelvic Biomechanics and Create More Room in Obstetric Diameters

Abstract

Dystocia in labor is still a clinical challenge. The "contracted pelvis" is the absence of pelvic mobility, which leads to fetal-pelvic disproportion, obstructed labor, and operative delivery. Maternal pelvis biomechanics studies by high technological techniques have shown that maternal shifting positions during pregnancy and labor can create more room in the pelvis for safe delivery. The external and internal pelvic diameters are related. The present study aims to evaluate the external obstetric pelvic diameters in shifting positions using a clinical technique suitable for daily practice in every clinical setting: the dynamic external pelvimetry test (DEP test). Seventy pregnant women were recruited, and the obstetric external pelvic diameters were measured, moving the position from kneeling standing to "hands-and-knees" to kneeling squat position. Results showed modification of the pelvic diameters in shifting position: the transverse and longitudinal diameters of Michaelis sacral area, the inter-tuberosities diameter, the bi-trochanters diameter, and the external conjugate widened; the bi-crestal iliac diameter, the bi-spinous iliac diameter, and the base of the Trillat's triangle decreased. The test showed good reproducibility and reliability. Linear correlations were found between diameters and between the range of motion of the diameters. The maternal pelvis is confirmed to modify the diameters changing its tridimensional shape. The pelvic inlet edge's inclination is inferred to be modified, facilitating the fetal descend. The pelvic outlet enlarged the transverse diameter, facilitating birth. The DEP test estimates the pelvic diameters' modification with postural changes, as magnetic resonance (MR) and computational biomechanics studies have demonstrated.

Can the Dynamic External Pelvimetry Test in Late Pregnancy Reveal Obstructed and Prolonged Labor? Results From a Pilot Study

“…The difference in amplitude between maternal positions of the bi-cristal diameter was statistically different between the two groups studied. Specifically, when we compared the measurements taken in the standing p1 position to those obtained in the "hands-and-knees" p2 position, the diameter decreased in the obstructed labor group, while it increased in the control group, in agreement with our previous results (Table 5) [15]. However, in the squat position, the bi-cristal diameter decreased more in the control group than in the obstructed labor group.…”

“…Our previous studies showed the ability of external obstetric pelvimetry to measure the maternal diameters in different positions. We found that as the woman changed her posture, the diameters varied, affirming the findings of studies that used high-tech methods to obtain these measurements [ 15 , 16 ].…”

“…We found that as the woman changed her posture, the diameters varied, affirming the findings of studies that used high-tech methods to obtain these measurements [15,16].…”

“…The pelvis appears as an in-section composed structure functioning as a dynamic whole and adapting to different human biological functions. DEP aspires to be a practical clinical test for evaluating pelvic mobility [15,16].…”

“…The larger external obstetric diameters estimated with the DP included the external anteroposterior conjugate, the bitrochanteric diameter, the bi-cristal diameter, and the iliac bi-spinous diameter (Figure 1F-1I). The bony landmarks of each diameter were accurately individualized in each patient [15,16]. Diameters were estimated in the following three positions which involved varying degrees of hip flexion on the pelvis: p1, "kneeling erect" position (the erect straight-leg position) (Figure 2A); p2, "hands-and-knees" position (the bent-leg position, with 90° flexed hips, or "all fours" position) (Figure 2B); and p3, "kneeling squat" position (Figure 2C).…”