Which Foetal-Pelvic Variables Are Useful for Predicting Caesarean Section and Instrumental Assistance?

Obstetrical Constraints and the Origin of Extended Postnatal Brain Maturation in Hominin Evolution

The origin of difficult birth is still a matter of debate in obstetrics. Recent studies hypothesized that early hominins already experienced obstructed labor even with reduced neonatal head sizes. The aim of this work is to test this hypothesis using an extant obstetrical sample with known delivery outcomes. Three delivery outcomes (i.e., instrument-assisted, Caesarean section, and vaginal birth) were evaluated using a discriminant analysis based on 131 mother-baby dyads and 36 feto-pelvic variables. This obstetrical sample was compared with 20 australopithecine "dyads" generated from the combination of six pelvic reconstructions (three for Australopithecus afarensis, two for A. africanus, and one for A. sediba) and three fetal head size estimations. The obstetrical analysis revealed that dystocic births can be predicted by pelvic features such as an anteroposteriorly flattened pelvic inlet. Australopithecines shared these pelvic morphologies with humans and had eutocic birth only for infants of 110 g brain size or smaller, equaling a human-like neonatal/adult brain size ratio of 25-28%. Although birth mechanism cannot be deduced, the newborn/adult brain size ratio was likely more human-like than previously thought, suggesting that australopithecines were secondarily altricial to circumvent instances of obstructed labor and subsequently require a prolonged postnatal brain growth period, implying some aspects of life history pattern similar to modern humans.

Accuracy and Reliability of Pelvimetry Measures Obtained by Manual or Automatic Labeling of Three-Dimensional Pelvic Models

(1) Background: The morphology of the pelvic cavity is important for decision-making in obstetrics. This study aimed to estimate the accuracy and reliability of pelvimetry measures obtained when radiologists manually label anatomical landmarks on three-dimensional (3D) pelvic models. A second objective was to design an automatic labeling method. (2) Methods: Three operators segmented 10 computed tomography scans each. Three radiologists then labeled 12 anatomical landmarks on the pelvic models, which allowed for the calculation of 15 pelvimetry measures. Additionally, an automatic labeling method was developed based on a reference pelvic model, including reference anatomical landmarks, matching the individual pelvic models. (3) Results: Heterogeneity among landmarks in radiologists' labeling accuracy was observed, with some landmarks being rarely mislabeled by more than 4 mm and others being frequently mislabeled by 10 mm or more. The propagation to the pelvimetry measures was limited; only one out of the 15 measures reported a median error above 5 mm or 5°, and all measures showed moderate to excellent inter-radiologist reliability. The automatic method outperformed manual labeling. (4) Conclusions: This study confirmed the suitability of pelvimetry measures based on manual labeling of 3D pelvic models. Automatic labeling offers promising perspectives to decrease the demand on radiologists, standardize the labeling, and describe the pelvic cavity in more detail.

Reconsidering the developmental origins of adult disease paradigm: The 'metabolic coordination of childbirth' hypothesis

In uncomplicated pregnancies, birthweight is inversely associated with adult non-communicable disease (NCD) risk. One proposed mechanism is maternal malnutrition during pregnancy. Another explanation is that shared genes link birthweight with NCDs. Both hypotheses are supported, but evolutionary perspectives address only the environmental pathway. We propose that genetic and environmental associations of birthweight with NCD risk reflect coordinated regulatory systems between mother and foetus, that evolved to reduce risks of obstructed labour. First, the foetus must tailor its growth to maternal metabolic signals, as it cannot predict the size of the birth canal from its own genome. Second, we predict that maternal alleles that promote placental nutrient supply have been selected to constrain foetal growth and gestation length when fetally expressed. Conversely, maternal alleles that increase birth canal size have been selected to promote foetal growth and gestation when fetally expressed. Evidence supports these hypotheses. These regulatory mechanisms may have undergone powerful selection as hominin neonates evolved larger size and encephalisation, since every mother is at risk of gestating a baby excessively for her pelvis. Our perspective can explain the inverse association of birthweight with NCD risk across most of the birthweight range: any constraint of birthweight, through plastic or genetic mechanisms, may reduce the capacity for homeostasis and increase NCD susceptibility. However, maternal obesity and diabetes can overwhelm this coordination system, challenging vaginal delivery while increasing offspring NCD risk. We argue that selection on viable vaginal delivery played an over-arching role in shaping the association of birthweight with NCD risk.

The impact of femoral rotation on sacroiliac articulation during pregnancy. Is there evidence to support Farabeuf's hypothesis by finite element modelization?

BACKGROUND

Counter-nutation movement is deemed crucial during the management of the birth process. It is a combination of lateral ilia expansion and backward displacement of the promontory resulting from the external rotations of the femurs producing an enlargement of the pelvic inlet. However, since its description by Farabeuf, this mechanism has never been challenged and analyzed in a dynamic finite element study.

METHODS

Based on a female pelvic mesh and sacroiliac ligaments, we simulated external rotations of both femurs with imposed rotation of the two acetabulum centers. We hypothesize that lateral ilia expansion generates a sacrum movement resulting in a backward displacement of the promontory and a pelvic inlet enlargement.

RESULTS

Finite element simulation confirms our hypothesis and reveals that ilio-sacro-transverse and axile ligaments play an essential role in this mechanism. Indeed, the increase in stiffness (ranging from 500 MPa to 750 MPa) of these ligaments accentuates the counter-nutation movement and the opening of the inlet. Instead of the anatomic congruence between the ilium and the sacrum, the sacroiliac ligaments may explain the counter-nutation. After a 6° of femur rotation, the inlet area increases to 11 cm2 (141 cm2 vs. 130 cm2). This enlargement could be noteworthy in case of obstructed labor or shoulder dystocia. Moreover, the association between external rotation and flexion of the femurs could be more efficient for opening the pelvic inlet.

CONCLUSIONS

Our result did not support the original assumption of Farabeuf. By revealing how postural adjustment increases the bony birth canal, this study provides essential information for the clinical management of the delivery.

Magnetic resonance imaging pelvimetric measurements as predictors for emergent cesarean delivery in obstructed labor

Objective

This study aimed to investigate the usefulness of various magnetic resonance imaging (MRI) pelvimetric parameters for predicting emergent cesarean delivery due to obstructed labor.

Study design

This was a prospective observational study. MRI pelvimetry was performed in cases of a clinically suspected maternal narrow pelvis, maternal short stature, fetal overgrowth, and abnormal placental position. MRI pelvimetry was performed at 34.7 ± 4.2 gestational weeks using a 1.5 T MRI system. The pelvic inlet angle, pelvic inclination, obstetric conjugate, sacral outlet diameter (SOD), and coccygeal pelvic outlet were measured in the sagittal section. The interspinous diameter and intertuberous diameter were measured in coronal sections. Fetal anomalies, cesarean deliveries before the onset of labor, and non-reassuring fetal status were excluded from the analysis.

Results

MRI pelvimetry was performed in 154 patients. After excluding 76 cases, including 19 cases of absolute cephalopelvic disproportion, 78 cases of trial of labor were included. Of these, 63 were vaginal deliveries and 15 were emergent cesarean deliveries due to obstructed labor. The cut-off value for body mass index (BMI) was 22.2, with an area under the curve (AUC) of 0.69, for predicting obstructed labor. The cut-off value for the SOD was 10.7 cm with an AUC of 0.69. BMI alone had a sensitivity of 80%, specificity of 66%, positive predictive value (PPV) of 36%, and negative predictive value (NPV) of 93%. When BMI and SOD were combined, sensitivity was 53%, specificity was 90%, PPV was 57%, and NPV was 89%. The odds ratio for emergent cesarean delivery was 5.42 (95% confidence interval 1.06-27.6, p = 0.041) if the SOD was less than the cut-off value in the binomial logistic regression analysis in cases with an BMI > 22.

Conclusion

We confirmed that MRI pelvimetry was a reliable tool for better patient selection for obstructed labor. The SOD was the best predictor of obstructed labor, with a cut-off value of 10.7 cm for women with a low BMI.

Pelvic inlet area is associated with birth mode

INTRODUCTION

To determine whether a pelvis is wide enough for spontaneous delivery has long been the subject of obstetric research. A number of variables have been proposed as predictors, all with limited accuracy. In this study, we use a novel three-dimensional (3D) method to measure the female pelvis and assess which pelvic features influence birth mode. We compare the 3D pelvic morphology of women who delivered vaginally, women who had cesarean sections, and nulliparous women. The aim of this study is to identify differences in pelvic morphology between these groups.

MATERIAL AND METHODS

This observational study included women aged 50 years and older who underwent a CT scan of the pelvis for any medical indication. We recorded biometric data including height, weight, and age, and obtained the obstetric history. The bony pelvis was extracted from the CT scans and reconstructed in three dimensions. By placing 274 landmarks on each surface model, the pelvises were measured in detail. The pelvic inlet was measured using 32 landmarks. The trial was registered at the German Clinical Trials Register DRKS (DRKS00017690).

RESULTS

For this study, 206 women were screened. Exclusion criteria were foreign material in the bony pelvis, unknown birth mode, and exclusively preterm births. Women who had both a vaginal birth and a cesarean section were excluded from the group comparison. We compared the pelvises of 177 women between three groups divided by obstetric history: vaginal births only (n = 118), cesarean sections only (n = 21), and nulliparous women (n = 38). The inlet area was significantly smaller in the cesarean section group (mean = 126.3 cm² ) compared with the vaginal birth group (mean = 134.9 cm² , p = 0.002). The nulliparous women were used as a control group: there was no statistically significant difference in pelvic inlet area between the nulliparous and vaginal birth groups.

CONCLUSIONS

By placing 274 landmarks on a pelvis reconstructed in 3D, a very precise measurement of the morphology of the pelvis is possible. We identified a significant difference in pelvic inlet area between women with vaginal delivery and those with cesarean section. A unique feature of this study is the method of measurement of the bony pelvis that goes beyond linear distance measurements as used in previous pelvimetric studies.

Obstetric dimensions of the female pelvis are less integrated than locomotor dimensions and show protective scaling patterns: Implications for the obstetrical dilemma

OBJECTIVES

The "obstetrical dilemma" hypothesis assumes that the modern human female pelvis serves two discrete functions: obstetrics and locomotion. We investigate whether these differing functions create observable patterns of morphological covariation and whether those patterns differ by height, weight, and age. This allows evaluation of evidence for canalization and phenotypic plasticity relevant to obstetric and locomotor function among a living female population.

METHODS

Landmarks (N = 86) were collected and inter-landmark distances were calculated (N = 36) on the pelvis and proximal femur of CT scans of living women aged 20 to 90 years (M = 93) receiving a routine CT scan. Partial least squares and relative SD of eigenvalues analyses were used to evaluate integration overall and within locomotor and obstetric modules, respectively. Ordinary Least Squared regression was used to evaluate scaling relationships between inter-landmark distances and height, weight, and age.

RESULTS

The obstetric pelvis was significantly less internally integrated than the locomotor pelvis. Many obstetric measurements were constrained in absolute terms relative to height; shorter women had relatively larger birth canal dimensions, and several key obstetric dimensions showed relative freedom from height. Lower weight women had some relatively larger obstetric and locomotor dimensions. Regarding age, younger women showed a few relatively larger outlet dimensions.

CONCLUSIONS

This study suggests that the obstetric pelvis and the locomotor pelvis function are morphologically distinct, with the obstetric pelvis showing relatively greater flexibility. These relationships between relative constraints support the hypothesis that the modern female pelvis shows evidence of both canalization and phenotypic plasticity in obstetric and locomotor structures.