Statistical analysis:
Univariate analysis was performed for categorical variables with the use
of the χ2 or Fisher’s exact tests. Continuous
variables were compared with the use of the Student t test or
Mann-Whitney U test. To evaluate the independent association
between CNM annual volume and maternal outcomes, we conducted
multivariate logistic regression modeling, adjusting for patient
demographic parameters and comorbidities: maternal age,
parity, gestational age, trial of labor after cesarean delivery (TOLAC),
second stage duration, persistent occipito-posterior,
2nd degree perineal tear and episiotomy. Additional
analysis was performed to assess whether association exists between
CNM’s annual volume and each neonatal outcome adjusting for: maternal
age, parity, gestational age, TOLAC and second stage duration. All tests
are 2-tailed; a probability value below .05 was considered statistically
significant. Analyses were carried out with SPSS software package
(version 25.0; IBM Corporation, Armonk, NY).
The study was approved by the local Institutional Review Board of SZMC
(IRB-0044-20, 15.08.2108) and was exempted from obtaining informed
consent as the study was based on patient records.