Background
Long continuous periods of working contribute to fatigue, which is an established risk factor for adverse patient outcomes in many clinical specialties. The total number of hours worked by delivering clinicians before delivery therefore may be an important predictor of adverse maternal and neonatal outcomes.
Objective
We aimed to examine how rates of adverse delivery outcomes vary with the number of hours worked by the delivering clinician before delivery during both day and night shifts.
Study Design
We conducted a retrospective cohort study of 24,506 unscheduled deliveries at an obstetrics center in the United Kingdom from 2008–2013. We compared adverse outcomes between day shifts and night shifts using random-effects logistic regression to account for interoperator variability. Adverse outcomes were estimated blood loss of ≥1.5 L, arterial cord pH of ≤7.1, failed instrumental delivery, delayed neonatal respiration, severe perineal trauma, and any critical incident. Additive dynamic regression was used to examine the association between hours worked before delivery (up to 12 hours) and risk of adverse outcomes. Models were controlled for maternal age, maternal body mass index, parity, birthweight, gestation, obstetrician experience, and delivery type.
Results
We found no difference in the risk of any adverse outcome that was studied between day vs night shifts. Yet, risk of estimated blood loss of ≥1.5 L and arterial cord pH of ≤7.1 both varied by 30-40% within 12-hour shifts ( P <.05). The highest risk of adverse outcomes occurred after 9–10 hours from the beginning of the shift for both day and night shifts. The risk of other adverse outcomes did not vary significantly by hours worked or by day vs night shift.
Conclusion
Number of hours already worked before undertaking unscheduled deliveries significantly influences the risk of certain adverse outcomes. Our findings suggest that fatigue may play a role in increasing the risk of adverse delivery outcomes later in shifts and that obstetric work patterns could be better designed to minimize the risk of adverse delivery outcomes.
Minimizing the risk of adverse outcomes at delivery is simultaneously a central goal and a major challenge for obstetric services. Previous studies have suggested that the timing of delivery influences the risk of adverse perinatal outcomes. In particular, the risk of neonatal death is higher for babies who are delivered outside of the normal 9:00–5:00 Monday-to-Friday working week. Other studies have produced conflicting evidence regarding whether the neonatal mortality rate is higher overnight or on weekends. However, neonatal death is a rare outcome (4 per 1000 births in the United States and 2.8 per 1000 births in the United Kingdom ), which is determined not only by intrapartum care but also is influenced heavily by the antenatal course and immediate neonatal treatment. There is less evidence regarding variation in the risk of other, more common, adverse maternal and neonatal outcomes depending on the timing of delivery. In this study, we focused on commonly occurring adverse outcomes that are related closely to intrapartum management and therefore most likely to be influenced by the timing of delivery.
Previous studies have considered adverse outcomes in relation to the day of the week and time of day at which delivery occurred. However, we hypothesize that the total number of hours worked by delivering clinicians before delivery may be a more important predictor of adverse outcomes than the day of the week or the time of day. Long continuous periods of working contribute to fatigue, which is an established risk factor for adverse patient outcomes in many clinical specialties; however, adverse outcomes have not been explored previously in relation to the number of hours worked. Fatigue is associated with numerous factors that contribute to poor outcomes and include decline in technical skills, slower reaction times, and riskier decision-making. Delivery can be a high-risk situation that requires identification of potential complications and decisive action. Identifying times of increased risk with respect to working patterns is important for optimizing quality and safety in obstetric services worldwide. The major advantage of this approach is that, in contrast to day and time of nonelective delivery, working patterns are modifiable, predictable, and under the control of individuals and institutions. Because previous work has suggested that increased rates of adverse outcomes may occur during night shifts compared with day shifts, it is possible that the effect of continuous hours worked before delivery is systematically different between day and night shifts. Particularly, if provider fatigue is a major contributing factor to the risk of adverse outcome, then the effect of continuous hours worked may be magnified in night compared with day shifts.
We aimed to determine (1) whether common adverse maternal and neonatal outcomes occur more frequently during night shift and (2) how risk of adverse outcomes varies with the number of hours worked before delivery, either during the day or overnight.
Materials and Methods
From January 2008 to October 2013, 29,112 women underwent delivery of a singleton, live-born infant of >24 completed weeks of gestation in a tertiary obstetrics center in the United Kingdom. We excluded 4611 women who gave birth by elective cesarean delivery. All other deliveries (24,506) were included in the sample, regardless of final mode of delivery. The working pattern for obstetricians within the study center follows 12-hour shifts from 8:00 am to 8:00 pm (day shift) and 8:00 pm to 8:00 am (night shift). This pattern remained constant throughout the study period. Midwives work the same 12-hour shifts as do the obstetricians in the study center. Handover periods occurred during the first 30 minutes of each shift.
The midwife assigned to the parturient recorded data regarding the pregnancy, delivery, and neonate in an electronic maternity database as soon as possible after birth. This database is maintained routinely as part of hospital records and was not created specifically for study purposes. The database is validated regularly by a rolling program of audits for which the original case notes are checked against the information recorded in the database. No patient-identifiable data were accessed during this research, which was performed as a provision-of-service study approved by the obstetrics center. Individual medical records were not accessed at any stage, and our institutions determined that Institutional Review Board approval was not required.
Available maternal, neonatal, and delivery characteristics included maternal age, maternal body mass index (measured at first-trimester booking), parity, maternal ethnicity, and birthweight (measured to the nearest gram). Gestational age (measured by crown-rump length at first-trimester ultrasound imaging) was recorded to the nearest week. Mode of delivery was classified as cesarean section, forceps, ventouse, or spontaneous vaginal delivery (including vaginal deliveries that occurred both cephalic and breech). Inductions of labor were included in the analytic sample, because the timing of delivery (during the day vs night shift) was not chosen by the woman or her caregivers. The mode of onset of labor was recorded as induction of labor “yes,” “no,” or “not applicable” (for women who were not in established labor when emergent delivery occurred). The year of delivery and day of the week on which delivery occurred were also available.
The type of health care professional who delivered the baby was classified as midwives, obstetricians with ≤5 years obstetric training, or obstetricians with >5 years obstetric training. In the study center, most spontaneous vaginal deliveries are performed by midwives, in line with usual practice across the United Kingdom. Instrumental deliveries and cesarean deliveries are performed only by obstetricians. A small number of spontaneous vaginal deliveries were also performed by obstetricians, but these were mainly high-risk cases (for example, preterm or breech presentation). In the study center, an obstetric team that consists of 3 doctors is available for every 12-hour shift. The team comprises a junior doctor with ≤2 years of obstetric experience, an obstetrician-in-training with ≥3 to ≤5 years of obstetric experience, and a senior obstetrician with >5 years of obstetric experience. Our cohort has the advantage that none of the clinicians provided obstetric care to any patients outside of the time recorded in the study. These clinicians were present solely for the purpose of attending women who were in labor and undertaking deliveries as required. Elective cesarean deliveries and any other scheduled obstetric procedures were undertaken by a separate, dedicated team. Inductions of labor are commenced on a scheduled day (including weekends) but at various times throughout the day and night as the workload allows.
Delay in neonatal respiration was recorded where spontaneous respiration was not achieved within 1 minute of delivery. Umbilical arterial pH was measured from cord blood that was taken immediately after delivery, where the delivering professional determined that this was required (9143 cases; 37.3%). This included all cases of operative delivery and any case for which there was concern regarding fetal well-being. Correlation between arterial and venous pH was checked to confirm accuracy of the measurements. Arterial pH was categorized as ≤7.1 or >7.1. Failed instrumental delivery was recorded in cases in which an operator applied an instrument but eventually delivered the baby by any other method (249/4042 cases; 6%). A critical-incident form was generated at delivery in the case of any obstetric or neonatal emergency, which included neonatal resuscitation, shoulder dystocia, maternal visceral injury, or any other event that generated an obstetric emergency call. The generation of a critical incident form was used to compile a composite outcome of rare and serious morbidity, which captures rare instances of neonatal death. No peripartum maternal deaths occurred in the center during the study period. Maternal blood loss was estimated immediately after delivery, with the use of suction blood collection and weighing of swabs and other pads. Blood loss was categorized as <1.5 or ≥1.5 L. Severe maternal perineal trauma was defined as any disruption to the anal sphincter complex.
We compared the characteristics of deliveries that occurred during the day vs night using binary logistic regression. We defined 2 cohorts: (1) all the deliveries that met our inclusion criteria during the study period (n=24,506) and (2) subset of these where delivery was performed by an obstetrician (n=7680). We hypothesized that, if the chance of an adverse outcome were significantly influenced by operator fatigue, then this would be more apparent in the obstetrician-only cohort, because complex operative procedures are more likely to have been performed. However, decision-making and management during labor is an important mediator of adverse outcomes, regardless of whether surgery is required; thus, we also present outcomes for the full dataset, including spontaneous vaginal deliveries. The results from this comparison of delivery characteristics were used to determine covariates that were included in the models that examined the risk of adverse delivery outcomes.
We compared adverse maternal and fetal outcomes during day and night shifts, both for all deliveries and for deliveries conducted by obstetricians only, using binary logistic regression. To control for variation in baseline complication rates between individual obstetricians and to account for multiple deliveries by the same operator, we also compared adverse outcomes during day and night shifts using mixed-effects logistic regression models that included a random effect for each individual obstetrician. Data from all obstetricians who delivered >100 babies during the study time period were included in this model (n=3203 deliveries by 28 operators).
Finally, we examined the risk of each adverse outcome dependent on the number of hours worked before delivery (ie, the time in full hours between the start of each shift and the time of delivery) using a generalized additive model in which all events were considered equivalent. This model incorporated a nonlinear term for hours worked before delivery on the risk of an adverse outcome, which was estimated with the use of cubic splines. This model allows us to avoid making any previous assumptions about the nature of the relationship between hours worked and the risk of adverse outcomes, thus allowing the model to best fit the data. Statistical significance of the nonlinear effect of hours worked was assessed with the use of a likelihood-ratio test. We fit a model for all deliveries and 2 separate models for deliveries that took place during night shifts and during day shifts.
Findings were considered statistically significant at an alpha level of .05. Power calculations were performed by Monte Carlo simulation. All analyses were conducted using the R statistical software package (version 2.14.1).
Results
Women who delivered overnight were more likely to be delivered by an obstetrician (with ≤5 years of experience [ P <.01]; with >5 years of experience [ P <.05]) and less likely to have labored before delivery ( P <.05; Table 1 ). Deliveries that occurred overnight were also less likely for women of higher parity (parity 1, P <.05; parity ≥2, P <.01), to involve induction of labor ( P <.05), or to involve the use of obstetric instruments (ventouse, P <.01; forceps, P <.05). Deliveries that occurred overnight were also associated with slightly lower gestational age ( P <.05). Although statistically significant, this difference represents a very small difference in actual gestational age, which is unlikely to be clinically meaningful. For women who required delivery by an obstetrician, deliveries overnight were more likely to be performed not in active labor ( P <.01; Table 1 ). Women who were delivered by obstetricians at night were less likely to be of higher parity ( P <.05) or to be delivered by obstetricians with >5 years of experience ( P <.05).
| Characteristic | All deliveries (n=24,506): day vs night | Deliveries by doctors (n=7680): day vs night | ||
|---|---|---|---|---|
| Odds ratio (95% confidence interval) | P value | Odds ratio (95% confidence interval) | P value | |
| Gestational age | 0.98 (0.96–0.99) | .02 a | 0.98 (0.96–1.01) | .25 |
| Birthweight | 1.00 (0.99–1.01) | .06 | 1.00 (0.99–1.00) | .18 |
| Maternal age | 0.99 (0.98–1.00) | .10 | 0.99 (0.99–1.00) | .16 |
| Maternal body mass index | 1.00 (0.99–1.01) | .33 | 1.00 (0.99–1.01) | .92 |
| Onset of labor | ||||
| Spontaneous | Reference | |||
| Induced | 0.82 (0.77–0.87) | <.01 b | 0.96 (0.87–1.05) | .36 |
| No labor | 1.17 (1.01–1.34) | .04 a | 1.31 (1.12–1.54) | <.01 b |
| Obstetrician experience | ||||
| Midwife | Reference | Not applicable | Not applicable | |
| Obstetrician, y | ||||
| ≤5 | 1.40 (1.16–1.68) | <.01 b | Reference | |
| >5 | 1.25 (1.02–1.52) | .03 a | 0.90 (0.82–0.99) | .04 a |
| Parity | ||||
| 0 | Reference | |||
| 1 | 0.94 (0.88–1.00) | .04 a | 0.98 (0.89–1.07) | .65 |
| ≥2 | 0.88 (0.81–0.94) | <.01 b | 0.86 (0.75–0.99) | .04 a |
| Delivery type | ||||
| Spontaneous vaginal delivery | Reference | |||
| Cesarean section | 0.89 (0.74–1.09) | .26 | 0.86 (0.71–1.04) | .13 |
| Forceps | 0.97 (0.79–1.18) | .04 a | 0.95 (0.77–1.16) | .59 |
| Ventouse | 0.95 (0.77–1.17) | <.01 b | 0.94 (0.76–1.15) | .54 |
After adjusting for delivery characteristics, we found no significant differences in the rates of adverse outcomes occurring among all deliveries during day vs night shifts ( Table 2 ). We also found no significant differences between rates of adverse outcomes between day vs night shifts for deliveries that were performed by obstetricians only ( Table 2 ).
