Are linear measurements or areas of birth canal planes more relevant to obstetric studies?
Author: Jennifer Eyre
Source: American Journal of Physical Anthropology, 2021, vol. 174, p. 29-30.
Publication type: Meeting Abstract
Abstract: The linear dimensions of the three major birth canal planes are frequently measured in studies concerning obstetrics in hominins and modern humans. However, the skeletal birth canal planes are not regular in shape and simple linear measurements may not accurately capture the two-dimensional area of each plane. In this study I created three-dimensional scans of ecogeographically varied modern human female pelves (N=128). For each pelvis one innominate and the sacrum was scanned, and the innominate was mirror-imaged in Geomagic to create a full pelvis. Anteroposterior and mediolateral measurements were taken in Geomagic following Tague and Lovejoy (1986). A novel method was utilized to measure the area of each plane. The 3D scan was exported as a 2D image into ImageJ where each plane was outlined based on landmarks and semilandmarks on the pelvis and sacrum. The area enclosed in each outline was then measured. The inlet was outlined in superior view; for the midplane the pelvis was removed superior to the ischial spines laterally, the inferior pubic symphysis anteriorly, and the articulation between the fourth and fifth sacral vertebrae posteriorly; the outlet was outlined in inferior view.
Linear dimensions correlated highly and significantly with measured areas (r>0.8, p<3x10^-32). However, a Student’s t-test identified significant differences between the linear dimensions and area of the inlet (p=0.00075) and outlet (p=9.3x10^-14). I conclude that while the measured areas may be more accurate, they may be less relevant because the perinate may be unable to take advantage of the entire area of each plane.