It is well known that parity indirectly and directly affects the human skeleton through biomechanical strain during pregnancy, birth, lactation, and sexual steroid hormone expression. Pelvic features are bony exostoses and lesions found on the pelvis and are frequently interpreted as parturition scars, although the direct causal factors remain unclear.
In this study, we created a weighted pelvic pattern index (PPI) by combining all pelvic features (preauricular sulcus, dorsal pubic pitting, extended pubic tubercle, ventral pubic pitting & exostoses, margo auricularis groove, sacral preauricular extension & notch) to evaluate its association with parity in three samples (one modern, and two from the 19th century).
This is the first study to define an index for assessing parity using statistical methods. We propose this index as a useful tool for assessing parity and we present a software tool for the easy applying the PPI in studies. The PPI was significantly associated with parity and age at death. A pelvis shape analysis revealed an association with an increase in pelvic width. Individuals with a minimum of four pelvic features were likely to be multiparous; however, elderly random bone modelling frequently weakens the association of the PPI with parity.
The PPI shows interpopulation differences between the modern and historic populations, suggesting different lifestyles, obstetrical treatments, etc., which is a limitation of the PPI. Consequently, we suggest using the PPI with caution at this stage of the research and continuing to test it in different populations with known parity.