Variations in pelvic canal and skull dimensions in South Africans : possible relationships and implications

Abstract

Cephalopelvic disproportion (CPD) is common among South Africans and a major cause of mortality and morbidity. The aim of this study was to explore the variations in pelvic and skull dimensions for their use in forensics and surgical procedures and for a better understanding of CPD and evolutionary processes. This study offered the unique opportunity to explore the variations of the pelvic canal and corresponding skull vault, in cadavers (148 pelves with 33 matching skulls) and on 3D computer tomography models (138 pelves with matching skulls) of black and white South Africans. Metric and geometric morphometric analyses were performed. Maternal and newborn anthropometric data were collected and correlated with birth outcomes (60 vaginal deliveries and 29 caesarean sections). Most linear pelvic canal dimensions were statistically significantly greater in females compared to males, in white compared to black South Africans and in white South Africans than reported in the literature. Biparietal diameter (BPD) and skull circumference were statistically significantly greater in white South Africans, while cranial length was statistically significantly greater in black South Africans. Skull dimensions were greater in males apart from the BPD, which was greater in white South African females. Correlations between skull and pelvic dimensions were more pronounced in females than in males. Contrastingly, to dimensions taken on the skull vault, maternal BPD was statistically significantly greater in black compared to white South Africans, while head circumferences were similar despite a statistically significantly shorter stature. Maternal anthropometrics were greater than reported in the literature. The white South African vaginal delivery group presented with the greatest newborn head circumferences, which were also greater than reported in the literature. Labour was longer in black South Africans. For forensic applications, the skull vault and pelvic canal dimensions delivered high accuracies for population and sex differentiation. Shape analyses of the pelvic canal and skull vault fared better in the prediction of population and sex (for population: pelvis: up to 97.87%; skull: up to 96.38%; for sex: pelvis: 100%; skull: up to 96.38%), when compared to linear dimensions (for population: pelvis: up to 85.33%; skull: up to 94.12%; for sex: pelvis: up to 87.68%; skull: up to 88.24%). Prior identification of population group improved sex discrimination by linear dimensions for both populations (pelvic canal: 89.16% in black South Africans and 96.36% in white South Africans; skull vault: 100% in both groups). Risk factors for CPD could include shorter stature, greater maternal and newborn head circumferences, especially in black South African women. Dietary changes may have worsened the obstetric dilemma by increasing neonatal size without increasing the stature and pelvic canal. Technically challenging operations may be experienced when performing pelvic or perineal surgery in black South Africans and in men because of the anatomically narrower pelves found in these groups. Future studies could confirm significance of the wider BPD noted in white South African women, whether a correlation between maternal and newborn head circumference exists and in the presence of a shorter stature, duration of labour (a reflection of CPD) is increased.