Midwifery Workforce Density Moderates the Association Between Independent Practice and Pregnancy Outcomes.

Midwife density moderates the association between independent midwifery practice and primary cesarean birth and preterm birth. Moderation may explain why prior studies found small or no changes in outcomes when states adopted independent practice. Moderation models can improve testing for associations with independent practice. Both midwife independent practice and increasing midwifery workforce size can be strategies to improve state pregnancy outcomes.