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.
Highlights
Childbirth is still a potentially complicated event for the woman and the newborn, with destructive health consequences in low-resource countries [1]
The patients' general characteristics are reported and described as mean and standard deviation (Table 1). 100% diameters had permitted to be measured. 1,509 out of 1,610 measurements were recorded for the statistical analysis: 101 measures were eliminated for procedural errors or difficult handwriting interpretation
The transverse diameter of the Michaelis sacral rhomboid area increased between the straight-leg and bent-leg position (p2-p1: mean of difference 9.5 mm; standard deviation (SD) 4.3; standard error of the mean (SEM) 0.5; 95% confidence interval (95% CI) 8.5-10.5 ; p
Summary
Childbirth is still a potentially complicated event for the woman and the newborn, with destructive health consequences in low-resource countries [1]. The "contracted pelvis" is the absence of pelvic mobility, which leads to fetal-pelvic disproportion, obstructed labor, dystocia, and operative delivery. The pelvic biomechanics and physiology during pregnancy, labor, and delivery have not yet been fully understood. Studies and research with magnetic resonance (MR), optoelectronic devices, and 3-D reconstruction computational analysis attempted to elucidate the biomechanics and dynamics of the maternal pelvic tissue anatomy during pregnancy for safe childbirth [2,3,4,5,6,7,8]. The freedom to move and standing positions throughout labor allows women to have better comfort during labor and the labor to proceed physiologically [9,10]. Shifting positions enables women to modulate the pelvic inlet, midlet, and outlet space, influencing and assisting the fetal head's passage during the descent. In the upright birthing positions, the maternal pelvis will offer less resistance to the force of progression in the pathway towards birth
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