Look up the term “pelvic canal” in the typical anatomy or obstetric textbook, and you likely will find a description such as this: “Well-built healthy women, who had a good diet during their childhood growth period, usually have a broad pelvis.”

Such a pelvis, the text continues, enables “the least difficulty during childbirth.”

But such characterizations have long been based on anatomical studies of people of European descent. In reality, the structure of the pelvic canal, the bony structure through which most of us enter the world, varies tremendously between populations, according to a new study in Proceedings of the Royal Society B.

The findings have implications for how obstetricians treat patients of color, the authors say. In the United States, racial disparities in maternal health care are prevalent. Compounding factors like interpersonal and institutional racism, poverty, poor health care access and environmental burdens disproportionately harm black mothers. These contribute to the risk of pregnancy-related deaths being three to four times higher for black women than for white women.

Limited prescriptions of what constitutes a “normal” pelvis or birthing process might lead doctors to perform unnecessary interventions — like induced labor, cesarean sections or the use of forceps — which can further exacerbate harm, said Lia Betti, an anthropologist at the University of Roehampton in London, and the study’s lead author.