Impact of Increasing Midwifery-Led Prenatal Care on Birth Outcomes: An Application of the g-Formula and Target Trial Emulation.

Background: Compared to undergoing prenatal care with a physician, care with a midwife reduces the risk of medical interventions and complications during labor and delivery among low-risk pregnant individuals. However, many analyses that assess the relationship between midwifery-led care and birth outcomes condition on live births, potentially inducing a type of collider bias.

Objective: The objective was to analyse the change in prevalence of caesarean deliveries, primary and secondary postpartum haemorrhage, obstetric trauma, and maternal infection under hypothetical scenarios where midwifery-led prenatal care was increased.

Methods: Our sample included commercially insured, midwifery-eligible pregnant people in an insurance claims data source. We used g-computation to assess the change in prevalence of caesarean deliveries, primary and secondary postpartum haemorrhage, obstetric trauma, and maternal infection if 10%, 20%, and 50% more pregnant people enrolled in prenatal care with a midwife rather than a physician, among a cohort of low-risk pregnant people with commercial insurance in the U.S. between 2004 and 2015.

Results: With a 50% increase in midwifery-led care compared with no increase, we found the prevalence of caesarean deliveries was reduced by 5.4 percentage points (95% confidence interval [CI] -5.7, -5.1) and of maternal infection decreased by 1.3 percentage points (95% CI -1.6, -1.0), while the prevalence of primary postpartum haemorrhage increased by 0.5 percentage points (95% CI 0.4, 0.6) and of secondary postpartum haemorrhage increased by 0.6 percentage points (95% CI 0.4, 0.7).

Conclusions: Increasing midwifery-led prenatal care reduced the prevalence of caesarean deliveries and maternal infections and slightly increased the prevalence of primary and secondary postpartum haemorrhage. Our results were similar to those of studies among live birth cohorts.