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.