Obstetricians are more likely to give Black women unnecessary cesarean sections, putting those women at higher risk for serious complications like ruptured surgical wounds.

That’s the conclusion of a new report of nearly one million births in 68 hospitals in New Jersey, one of the largest studies to tackle the subject.

Even if a Black mother and a white mother with similar medical histories saw the same doctor at the same hospital, the Black mother was about 20 percent more likely to have her baby via C-section, the study found.

The additional operations on Black patients were more likely to happen when hospitals had no scheduled C-sections, meaning their operating rooms were sitting empty. That suggests that racial bias paired with financial incentives played a role in doctors’ decision-making, the researchers said.

How that bias creeps in is not entirely clear. Doctors may rush to perform a C-section faster for Black women, worried about the well-known racial disparities in childbirth outcomes. Black women may feel less empowered to push back against the suggestion of C-section when their labor is not progressing — or, when they do push back, they may be less likely to have their concerns taken seriously.

“Physicians may have certain beliefs about Black women,” said Janet Currie, a health economist at Princeton University and a co-author of the study. “They might not be listening to Black women as much, or be more afraid that something will go wrong.”