Association between time of day and performance, indications, and outcomes of obstetric interventions among nulliparous women delivering at term

Abstract

Objective

The objective of this study is to determine whether there is an association between delivery time and obstetric interventions, as well as maternal and perinatal outcomes.

Study design

Retrospective cohort study of nulliparous women delivering singleton, vertex, live births at ≥37 weeks gestation at a single center from 2014 to 2015. Nighttime deliveries were designated as those occurring between 18:00 and 05:59 h. The primary outcomes were obstetrical interventions (cesarean delivery, operative vaginal delivery, episiotomy). Secondary outcomes included indications for operative deliveries, as well as maternal and perinatal outcomes.

Results

Of 7691 women eligible for inclusion, 3707 (48.2%) delivered during the nighttime. Women who experienced nighttime deliveries had no demographic or clinical differences compared with women delivering during the daytime. Women delivering during the nighttime had greater odds of cesarean delivery (OR 1.27, 95% CI 1.14–1.43) and operative vaginal delivery (OR 1.83, 95% CI 1.20–2.78). Women who delivered at night were also more likely to have neonates with a 5 min Apgar score <7 (OR 1.59, 95% CI 1.08–2.32) and umbilical artery pH < 7.0 (OR 1.76, 95% CI 1.18–2.63). There were no differences observed in any of the other outcomes examined.

Conclusions

Delivery during the nighttime is associated with alterations in some obstetric interventions and perinatal outcomes

Introduction

Investigations of hospital care suggest there may be differences in quality of care based on the time of day. Outside of obstetrics, it has been suggested that nighttime is associated with greater odds of patient morbidity due to hypothesized differences in staffing or impaired physician cognition [1–3]. However, the unpredictable nature of parturition necessitates around-the-clock management of women in labor.

In obstetrics, timing of delivery is a variable that may independently be associated with birth outcomes due to issues such as inadequate staffing, lower hospital capacity, or provider fatigue that may impact physician decision-making. Previous studies suggest nighttime deliveries may be associated with increased perinatal morbidity and mortality [4–8]. Nighttime delivery has been associated with lower cord umbilical artery pH, intrapartum and early neonatal mortality, low 5 min Apgar scores, and neonatal intensive care unit (NICU) admissions [4, 9–11]. Other studies have suggested increased risk of neonatal encephalopathy, neonatal seizures, birth asphyxia, and birth injury associated with nighttime deliveries in comparison with daytime deliveries [12, 13]. Perinatal morbidity and mortality in these cohorts have been attributed to intrapartum anoxia and asphyxia [14–18]. Nighttime deliveries have also been associated with increased risk of maternal morbidity, such as anal sphincter injury and post-operative complications after unplanned cesarean delivery [4, 19, 20]. These trends are particularly demonstrated at periods of time when fewer senior physicians and ancillary staff are available in-house [9, 10]. In contrast, other data suggest that there are no differences in morbidity by time of day; including no difference in complications from cesarean deliveries between nighttime and daytime deliveries [21, 22].

Although existing data suggest potential differences in outcomes based on timing of delivery, it remains unclear whether physician decision-making in the intrapartum context varies by time of day [21–24]. Developing a better understanding of the diurnal pattern of labor and delivery, and associated physician decision-making differences by time of day may allow us to optimize care. For example, previous studies have demonstrated that physicians on a night float call schedule are more likely to have patients undergo a trial of labor after cesarean and achieve successful vaginal birth after cesarean [25]. Differences in physician decision-making and cognition based on work schedules may contribute to differences in care provided and potentially to performance of obstetric interventions. Thus, the objectives of this study are to determine whether there are associations between delivery time and obstetrical interventions, as well as maternal and perinatal outcomes at a single high-volume tertiary care center.

Materials and methods

This is a retrospective cohort study of nulliparous women delivering at a single large volume academic center between January 2014 and December 2015. Inclusion criteria included nulliparous women with term (≥37 weeks of gestation), singleton, cephalic-presenting, live births. Women who delivered via a planned cesarean were excluded. All data were abstracted from the electronic medical record.

Delivery time was dichotomized between daytime deliveries and nighttime deliveries, with nighttime deliveries designated as those occurring between 18:00 and 05:59 h. This time period was chosen to most fully reflect the time period of decreased labor and delivery coverage, as both morning and evening team sign-out occurs in the daytime interval. Of note, at this institution, the twice-daily formal sign-out of laboring patients occurs among residents, fellows, and the supervising covering attendings, but private providers caring for laboring patients have variable schedules that may include shorter or longer periods of coverage and varying systems for sign-out. At this institution, over 140 physician and midwife attending providers cover labor and delivery alongside 51 residents and fellows. Residents are involved in the care of all patients, although may not be present at every delivery. Thus, patients may have multiple providers involved in their care; for this reason, the designation of nighttime delivery was chosen as a static concept to reflect changes that may occur at night rather than an individualized approach accounting for the many nuances of different provider schedules. In addition, at this institution, inductions of labor are scheduled around the clock, including on the night shift. Medical and elective inductions of labor are thus scheduled at all times of day. Staffing on weekend days and nights are similar to weekday days and nights, respectively.

Maternal demographic and clinical characteristics were analyzed by delivery time. These characteristics included age at delivery, maternal race and ethnicity, insurance status, body mass index (BMI), gestational age at delivery, induction of labor (vs. spontaneous labor), use of epidural analgesia, and birthweight. Time of delivery was also compared across different provider types (general obstetricians, maternal–fetal medicine specialists, and certified nurse midwives).

The primary outcomes consisted of obstetric interventions that were chosen to be reflective of physician decision-making in the intrapartum setting. These included the following: mode of delivery (cesarean delivery, operative vaginal delivery, and spontaneous vaginal delivery) and episiotomy. Episiotomy analyses were restricted to women who underwent spontaneous and operative vaginal deliveries. We hypothesized there may be more obstetrical interventions occurring in the nighttime period due to alterations in provider practices or behaviors at night.

Secondary outcomes included indications for any operative deliveries (cesarean or operative vaginal). Indications for cesarean delivery included non-reassuring fetal heart tracing, labor arrest (failed induction or active phase arrest), arrest of descent, and other indications. Indications for operative vaginal delivery included non-reassuring fetal heart tracing, prolonged second stage of labor, and maternal exhaustion. Secondary outcomes also included maternal and perinatal outcomes. Maternal outcomes included third or fourth degree perineal lacerations, postpartum hemorrhage (defined as > 500 ml estimated blood loss for vaginal deliveries and > 1000 ml estimated blood loss for cesarean deliveries), and maternal packed red blood cell transfusion. These outcomes were chosen, as they may reflect outcomes associated with prolonged labor or operative deliveries. Perineal laceration analyses were restricted to women who underwent vaginal delivery. Perinatal outcomes examined included 5 min Apgar score < 7, cord umbilical artery pH < 7.0, and NICU admission. Cord gas collection was universal for all patients when possible after delivery.

An additional sensitivity analysis was performed for the above primary and secondary outcomes after excluding women who underwent inductions of labor, as it is possible this subgroup may have introduced bias by interfering with the natural timing of delivery.

Patient characteristics and outcomes were compared using the Student’s t-test for continuous variables and χ² or Fisher’s exact test where applicable for categorical variables. Relative risk ratios and 95% odds ratios (ORs) were estimated using multinomial logistic regression for the multinomial outcomes (delivery mode and indications for operative deliveries). Unadjusted ORs and 95% confidence intervals (CIs) were estimated using logistic regression for the binomial outcomes. All tests were two-tailed and p < 0.05 denoted statistical significance. Multivariable regression models were not performed given the lack of statistically significant potential confounders on bivariable analyses. All statistical analyses were performed with Stata v. 14 (StataCorp, College Station, TX). This study was approved by the Institutional Review Board of Northwestern University.

Results

A total of 7691 women met inclusion criteria during the study period. Of these, 48.2% (n = 3707) delivered at nighttime. On bivariable analysis, maternal demographic and clinical characteristics were similar between women who underwent daytime vs. nighttime deliveries (Table 1). There were no differences between the two groups by maternal age, race or ethnicity, insurance status, BMI, or gestational age at delivery. In addition, there were no differences by clinical characteristics such as use of epidural analgesia, induction of labor, or birthweight. Finally, there were no differences by delivery provider, including general obstetricians, maternal–fetal medicine specialists, and midwives.

Table 1.

Demographic and clinical characteristics by time of delivery

	Night delivery (18:00–05:59 h)	Day delivery (06:00–17:59 h)	P-value
	n = 3707	n = 3984
Maternal age, years	30.8 ±5.1	30.8 ±5.0	0.65
Maternal race/ethnicity			0.36
Non-Hispanic White	1999 (53.9)	2184 (54.8)
Non-Hispanic Black	319 (8.5)	309 (7.8)
Hispanic	324 (8.7)	324 (8.1)
Asian	318 (8.6)	323 (8.1)
Other/unknown	747 (20.2)	844 (21.2)
Public insurance	540 (14.6)	535 (13.4)	0.15
Delivering provider			0.72
General obstetrician/gynecologist	3233 (87.2)	3464 (87.0)
Maternal-fetal medicine	144 (3.9)	147 (3.7)
Midwife	330 (8.9)	373 (9.4)
Body mass index at delivery, kg/m2	29.9±5.3	29.8 ±4.1	0.35
Induction of labor	744 (20.1)	731 (18.4)	0.06
Epidural analgesia	3456 (93.2)	3727 (93.6)	0.57
Gestational age at delivery, weeks	39.6±1.1	39.6±1.1	0.66
Birthweight, g	3364 ±457	3370±439	0.53

Data reported as N(%) or mean ± SD

On bivariable analysis of the primary outcomes, differences were noted for mode of delivery. Women delivering during the nighttime were more likely to experience cesarean delivery (relative risk ratio (RRR) 1.83, 95% CI 1.20–2.78) and operative vaginal delivery (RRR 1.27, 95% CI 1.14–1.43) compared with women who delivered during the daytime. There were no differences for indication for operative vaginal delivery by time of day. However, women delivered by cesarean delivery were more likely to be delivered for arrest of descent at nighttime in comparison with non-reassuring fetal heart tracing (52.7% vs. 44.5%, p = 0.005; RRR 1.59, 95% CI 1.23–2.06) (Table 2). There were no differences in frequency of episiotomy by time of day of delivery.

Table 2.

Obstetric interventions and indications for operative delivery by time of delivery

	Night delivery (18:00–05:59 h)	Day delivery (06:00–17:59 h)	P-value	Unadjusted RRR or OR (95% CI)
	n = 3707	n = 3984
Mode of delivery			<0.001
Spontaneous vaginal delivery	2885 (77.8)	3269 (82.1)		(ref)
Operative vaginal delivery	58 (1.6)	36 (0.9)		1.83 (1.20–2.78)
Cesarean delivery	764 (20.6)	679 (17.0)		1.27 (1.14–1.43)
Operative vaginal delivery indication			0.315
Non-reassuring fetal heart tracing	28 (48.3)	23 (63.9)		(ref)
Prolonged second stage of labor	18 (31.0)	7 (19.4)		2.11 (0.75–5.93)
Maternal exhaustion	12 (20.7)	6 (16.7)		0.30 (0.53–5.06)
Cesarean delivery indication			0.005
Non-reassuring fetal heart tracing	159 (20.8)	190 (28.0)		(ref)
Labor arrest	198 (25.9)	183 (26.9)		1.29 (0.97–1.73)
Arrest of descent	403 (52.7)	302 (44.5)		1.59 (1.23–2.06)
Other	4 (0.52)	4 (0.59)		1.19 (0.29–4.85)
Episiotomy	111 (3.8)	133 (4.0)	0.607	0.93 (0.72–1.21)

Data reported as N(%) RRR or OR

CI confidence interval, OR odds ratio, RRR relative risk ratios

Maternal outcomes, including third or fourth degree perineal lacerations, postpartum hemorrhage, or maternal blood transfusion, did not differ significantly between the two groups (Table 3). Regarding neonatal outcomes, women who underwent nighttime delivery were more likely to have neonates with a 5 min Apgar score < 7 (OR 1.59, 95% CI 1.08–2.32) (Table 3). Women who underwent nighttime delivery were also more likely to have neonates with cord umbilical artery pH < 7.0 (OR 1.76, 95% CI 1.18–2.63). There was no difference in frequency of NICU admission between daytime vs. nighttime deliveries (Table 3).

Table 3.

Maternal and neonatal outcomes by time of delivery

	Night delivery (18:00–05:59 h)	Day delivery (06:00–17:59 h)	P-value	Unadjusted OR (95% CI)
	n = 3707	n = 3984
Maternal outcomes
Third or fourth degree perineal laceration	168 (5.7)	203 (6.1)	0.47	0.93 (0.75–1.14)
Postpartum hemorrhage	214 (5.8)	205 (5.2)	0.23	1.13 (0.93–1.38)
Maternal pRBC transfusion	21 (0.6)	23 (0.6)	0.95	0.98 (0.54–1.78)
Neonatal outcomes
5 Min Apgar score < 7	66 (1.8)	45 (1.1)	0.02	1.59 (1.08–2.32)
Cord umbilical artery pH <7.0 (n = 5898)	66 (2.3)	39 (1.3)	0.005	1.76 (1.18–2.63)
NICU admission	97 (2.6)	83 (2.1)	0.12	1.26 (0.94–1.70)

Data reported as N(%) or OR

CI confidence interval, NICU neonatal intensive care unit, OR odds ratio, pRBC packed red blood cells

The results of the sensitivity analysis after excluding inductions of labor were largely unchanged for the primary and secondary outcomes of the study. There were a total of 744 (20.1%) women who underwent induction of labor resulting in nighttime delivery and 731 (18.4%) women who underwent induction of labor resulting in daytime deliveries. In analysis excluding these women, there were no differences in maternal demographic and clinical characteristics by time of delivery. Significant differences in mode of delivery by time of day persisted. In particular, women delivering during the nighttime were more likely to experience cesarean delivery (RRR 2.05, 95% CI 1.29–3.27) and operative vaginal delivery (RRR 1.28, 95% CI 1.11–1.47) compared with women who delivered during the daytime. Women delivered by cesarean were similarly more likely to be delivered for arrest of descent at nighttime in comparison with non-reassuring fetal heart tracing (RRR 1.58, 95% CI 1.15–2.17). There were no differences for indication for operative vaginal delivery or frequency of episiotomy by time of day. Women who underwent nighttime delivery in the sensitivity analysis were again more likely to have neonates with a cord umbilical artery pH < 7.0 (OR 1.78, 95% CI 1.11–2.86); however, they did not experience a significant difference for neonates with a 5 min Apgar score < 7 (OR 1.54, 95% CI 0.98–2.41). Differences in maternal outcomes and frequency of NICU admissions by time of delivery remained unchanged on sensitivity analysis.

Comment

Outside of obstetrics, nighttime hospital care has been hypothesized to be a time of greater risk for patient morbidity and mortality [1–3]. Our investigation into the relationship between time of delivery and obstetric care suggests this effect may also exist in obstetrics. Prior work suggested nighttime deliveries were associated with greater neonatal morbidity and our observational study corroborates existing evidence about differences between time of delivery with regard to obstetrical care. A number of hypotheses exist about the potential mechanisms by which nighttime care is associated with differences in obstetric practice and outcomes. As demonstrated previously by our group, physician behavior may be influenced by obstetric group call schedules [25]. Multiple prior studies have also highlighted the association between decreased senior physician availability and increased maternal and neonatal morbidity and mortality [4, 19].

Our study demonstrates that delivery at nighttime is associated with differences in performance of obstetrical interventions, specifically cesarean and operative vaginal delivery. We additionally identified indications for cesarean shifting at nighttime, as women were more likely to be delivered by cesarean for arrest disorders compared with non-reassuring fetal heart tracings. Fewer available senior physicians and ancillary staff at nighttime may contribute to different decisions made in nuanced intrapartum situations or to poorer neonatal outcomes due to delay in diagnosis or management of emergent situations as demonstrated through differences in indication for mode of delivery. In addition, it is possible that nighttime providers are less tolerant of prolonged labor due to provider fatigue, or that nighttime physicians have lower tolerance for labor augmentation with oxytocin due to the risk of uterine tachysystole and associated fetal distress. This may in turn contribute to arrest disorders that consequently increase the likelihood of cesarean delivery.

Our findings also highlighted greater odds of adverse neonatal outcomes when delivery occurred at night, such as a 5 min Apgar score < 7 and cord umbilical artery pH < 7.0. These differences in indications for mode of delivery may be associated with lower Apgar score and umbilical artery pH in neonates delivered at nighttime. However, it remains unclear whether the identified differences in neonatal outcomes are consequences of the overall increased likelihood of delivery by operative delivery at nighttime or as a result of the decreased likelihood of proceeding with a cesarean delivery at night for fetal distress. Each of these hypotheses warrants further study in order to better understand the findings herein.

Differences in mode of delivery and indications for performance of obstetric interventions persisted on sensitivity analysis after excluding women who underwent induction of labor. Although 5 min Apgar score < 7 no longer remained significant on sensitivity analysis, this is most likely due to a lack of power to detect differences in the small number of neonates with this adverse outcome. As both medical and elective inductions are scheduled at all times of day at this institution, these findings are not surprising. The overall findings of this study may therefore be generalized to spontaneous labor as well as inductions of labor.

This study is unique in that it was performed at a large urban academic center with a diverse patient population and a wide variety of obstetric providers, thus enhancing generalizability. However, our study also has a number of limitations to consider. Unlike some previous studies, our analysis did not identify a significant association between time of delivery and other adverse neonatal outcomes such as NICU admissions, possibly due to lack of power. Although there was no difference between type of delivering provider for daytime and nighttime deliveries, further stratification of providers by level of training and years of experience was not possible, but may help address whether adverse birth outcomes are due to decreased senior physician presence at nighttime. We are additionally unable to account for such issues as provider call type, provider fatigue, or provider length of work before the delivery, as well as availability of support staff and equipment such as forceps, vacuum, or operating room availability at nighttime, all of which may be potential confounders. In addition, we accounted for time of delivery as the exposure of interest, whereas it is possible that the hours preceding delivery could be equally important; deliveries taking place soon after shift change may be subject to misclassification bias. Although analyzing a few specific outcomes over small blocks of time may be an interesting consideration for future studies, we chose a 12 h block time frame as the most clinically relevant period of time, because the time period designated as daytime is inclusive of both shift changes, thus is reflective of the period of greatest staffing and resource availability. Finally, these findings were in the context of a large center with house staff present and with around-the-clock availability of specialty and subspecialty providers, and thus findings may not be fully generalizable to other practice settings.

Although time of day of delivery is largely outside of obstetricians’ control, differences in clinical decision-making such as mode of delivery and indications for cesarean section may impact obstetric outcomes during daytime vs. nighttime delivery. As our study provides further evidence that nighttime delivery is associated with differences in obstetric practices, further understanding of how physician decision-making varies by time of day may help generate areas of intervention to optimize care provision and subsequent outcomes.