Setting
Shaare Zedek Medical Center (SZMC) is an academic medical center with a
large obstetric service. The Labor and Delivery Department attends
approximately 15,000 deliveries annually in 16 fully equipped delivery
suits. The National Insurance Health Plan covers antepartum, labor and
delivery, postpartum and neonatal care.
Briefly, in Israel, CNMs undergo an extensive training program before
being licensed by the Israel Ministry of Health. Only registered
baccalaureate nurses, are eligible to enroll in the CNM program. The
training program includes a minimum of 350 hours of theoretical studies,
630 hours of clinical practice, delivery of 50 vaginal deliveries,
attending an additional 100 women in various stages of their labor while
being mentored by an experienced CNM clinical instructor based on “one
on one” preceptorship.
In our academic medical center, ”shared model of care” applies, during
the labor and delivery, excluding the prenatal care. Women in labor
following uncomplicated pregnancies with a singleton vertex presentation
are attended, managed and delivered by CNMs. The obstetrician is
ultimately responsible for the overall events and outcomes transpiring
in the delivery room. In the event of complications and the need for
intervention, the obstetrician is involved. The decision making process
is led by the board-certified obstetricians. All vacuum assisted vaginal
deliveries (VAVD) CDs, multifetal gestations and non-vertex presenting
fetuses are managed / performed by obstetricians.
CNMs work shifts are every eight hours, CNM are assigned to a parturient
based on availability by the CNM- shift controller. It is customary that
one CNM is responsible for two parturient at the same time; usually one
is in advanced labor and the other in early labor, or undergoing
induction of labor. Occasionally, a situation may arise when both of the
parturients in the CNM’s care progress simultaneously to the second
stage of labor whereby, another CNM is assigned to the delivery one of
these parturients, albeit she did not care for the woman during the
progress of her labor.
All CNMs who attended and assisted at least one annual vaginal birth
during the study period were included in this study. Any cutoff of
number of vaginal births attended annually by a single CNM chosen to
evaluate the association between CNM’s annual workload and incidence of
maternal and neonatal complications would have been arbitrary; for the
purpose of this study, the median was used as a cutoff value. The annual
number of vaginal births attended was determined for each individual CNM
separately for every year during the study period and was assigned to
the respective group. Every birth delivery was assigned to either
”low-volume” group– a vaginal birth which was attended by a CNM who
attended less than the median for that year or to ”high-volume” group–
a vaginal birth which was attended by a CNM who attended more than the
median for that year. The high group was chosen as the reference group
for analysis. All CNMs names were replaced with random numbers to allow
a “blind” analysis.
In order to further evaluate the association between individual CNM
workload and outcome and to seek a threshold value for the CNM optimal
experience and outcome, additional analysis according to ten deciles of
annual volume was performed. Every delivery was assigned to its
respective group by the CNM decile. To avoid possible confounding by
time, groups were assigned each year separately for all analyses. We
also performed a subgroup analysis of first vaginal delivery with the
same methodology as described above.