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

Area of Science:

• Obstetrics and Gynecology
• Public Health Policy
• Maternal Health Outcomes

Background:

• Previous studies on independent midwifery practice showed minimal changes in cesarean and preterm birth rates.
• The role of midwife density in moderating these outcomes was not adequately controlled for.

Purpose of the Study:

• To investigate if local midwife density moderates the association between state-level independent midwifery practice and key pregnancy outcomes.
• To analyze the impact of midwife density on cesarean birth and preterm birth rates.

Main Methods:

• Analysis of 875,156 birth records from 6 states using State Inpatient Databases.
• Midwife density categorized as none, low (<4.5/1000 births), or high (≥4.5/1000 births).
• Multivariate logistic regression models with interaction terms to test moderation by midwife density.

Main Results:

• Restricted midwifery practice correlated with higher odds of primary cesarean birth and preterm birth.
• Significant moderation by midwife density was observed for both outcomes.
• The highest odds of preterm birth (OR, 3.50) occurred in high midwife density counties with restricted practice.

Conclusions:

• Midwife density is a critical factor moderating the relationship between independent midwifery practice and pregnancy outcomes.
• Findings suggest that both independent midwifery practice and increased midwife workforce size are strategies to enhance state pregnancy outcomes.
• Moderation models offer improved analysis for independent practice associations and policy development.