Results
During the study period, 197,185 deliveries were recorded; 140,855
(71.4%) deliveries met the study inclusion criteria
(Figure 1 ). A total of 159 CNMs
worked during the study period at the SZMC, attended at least one
delivery annually and were included in the study. The median annual
vaginal births attended, during the study period was 152 deliveries
[114-195]; 70,849 deliveries (50.3%) were assigned to the ”low
group” and 70,006 deliveries (49.7%) to the ”high group” in accordance
with the CNM ”low” and ”high” annual volume, respectively.
Per definition, there was a difference in the number of deliveries
attended by the CNM in the two groups; the ”low volume” group was
delivered by CNMs with an average of 108.3±30.5 deliveries annually and
the ”high volume” group was delivered by CNMs with an average of
208.2±49.6 deliveries annually. The ”low volume” group was delivered by
CNMs with a longer mean practice duration as compared with the ”high
volume” group (12.6±10.7 vs 7.5±8.2 years, p<0.001).
Several statistical significant differences were noted in maternal
characteristics between groups and these are detailed
in Table 1 . These differences
were noted in the following variables (low volume vs. high volume):
higher maternal age, higher gravidity, higher parity, higher rate of
previous CD, advanced gestational age at delivery, higher rates of
diabetes mellitus, lower rate of augmentation of labor, lower rate of
persistent occiput posterior and shorter duration of second stage. The
incidence of previous miscarriages, hypertensive pregnancy disorders,
fertility treatments, induction of labor, epidural analgesia,
chorioamnionitis as well as prolonged second stage did not differ
significantly between groups.