Sacral preauricular extensions and notches as parts of a 'Pelvic Pattern' may provide information on past pregnancies and parturitions.

During the analyses of several hundred prehistoric individuals from Austria, we observed that some women display a "Pelvic Pattern" at the innominate bones and the sacrum, i.e. specific combinations of pronounced expressions of pelvic features. We recorded classic pelvic features (dorsal pubic pitting, preauricular sulcus, extended pubic tubercle) as well as new ones (SPE: sacral preauricular extension, a ventrally pointing flat bone formation at the ventrosuperior margin of the ala ossis sacri; SPN: sacral preauricular notch, a loss of convexity at the same location; CF: corresponding facets at the ilium), and some less well-known features, i.e. the margo auricularis groove, ventral pubic exostoses and lesions. To quantify the assessed features, we developed a specific formula to calculate the 'Pelvic Pattern Index' (PPI). As pregnancies and/or parturitions are suspected to contribute to or be at least partly causative of the occurrence of pelvic features, we analyzed 48 well-preserved female individuals and 15 males from identified skeletal collections with obstetric information in Geneva and London. In these collections, we found a pelvic pattern of at least four out of ten distinctly expressed pelvic features only in multiparous females, but not in nulli- or primiparous females or in males. This pattern was found in 40.6% of the multiparous females and 29.2% of all females from the identified collections, compared to 56.1% of well-preserved prehistoric females with unknown parity status from Austria (n = 41). The mean PPI of the multiparae from the identified collections is 0.25, compared to a mean PPI of 0.19 for all women from the identified collections, and 0.28 for the prehistoric female individuals. We conclude from this that a high PPI (≥ 0.30), especially in cases where SPE or SPN are present, can give insights into past motherhood.