Busy day effect on intrapartum adverse maternal outcomes – a population‐based study of 601 247 singleton deliveries

Giving birth is an individual and often unpredictable process. Elective Caesarean is the only delivery mode which can be scheduled beforehand. The nature of the delivery process causes challenges to delivery unit organisations. Daily inconsistent occurrences and varying patient flow in delivery units can cause a range from quiet to busy time periods compared to unit´s optimal period in terms of capacity and staffing. Delivery unit organisations have a responsibility to ensure patient safety and keep the balance in quality of care despite of these daily changes in patient flow [1]. We have shown in the earlier studies the occurrence of daily delivery volume changes in particular within small delivery units (< 1000 annual deliveries), where the variation of daily patient flow is more prominent compared to the larger ones (Vilkko R, Räisänen S, Stefanovic V, Gissler M, Heinonen S: Patient flow unevenness in different sized delivery hospitals – an 11-year register study of 610 227 deliveries, unpublished). This implies that hospital capacity may become overloaded and have an effect on the delivery unit practises. As a consequence, earlier results also indicate that busy days tend to produce excessive interventions during labour (Vilkko R, Räisänen S, Gissler M, Stefanovic V, Heinonen S: Busy day effect on the use of interventions during labour – A population-based register study of 601 247 singleton deliveries, unpublished). For these reasons, busy days in delivery units can be seen as a risk factor for adverse maternal outcomes. However, the other existing evidence on this is limited since quality indicators [2] are more often assessed and based on annual or monthly statistics [3‐8] or hospital level acuteness [9] or even time of the day [10, 11]. The busy day effect on maternal outcomes is a less studied topic. To understand the busy day effect, it is possible to collect hospital level quality markers on a daily basis for outcome measures which are easy to identify, occur frequently enough and vary sufficiently among hospitals [12]. In this study setting, varying patient flow days have been defined as quiet, optimal and busy and have set these definitions as exposures to select adverse maternal outcome measures as blood transfusions, manual removal of the placenta (MRP) and obstetric anal sphincter injuries (OASIS). Daily delivery frequencies and ranges (min-max) were calculated for each delivery unit and then stratified by the delivery unit´s annual delivery volume and profile to make a hospital level comparisons possible. The aim of this study is to analyse the busy day effect on selected intrapartum maternal outcomes in five categories of delivery units with different annual delivery volumes or profiles.

This study was conducted in Finland, a Nordic country with 5.5 million inhabitants and publicly funded free of charge maternity care services used by 99 % of pregnant women. Private delivery services are not available. The data for this retrospective population-based study included 601 247 singleton deliveries from 26 delivery hospitals in 2006─2016. Multiple pregnancies (n = 9149) and deliveries (n = 24 414) occurring in delivery units (n = 8), which were closed because of the low annual delivery volume during the study period, were excluded. Data were gathered from the Finnish Medical Birth Register (MBR). The MBR data include all diagnoses (defined by International Statistical Classification of Diseases and Related Health Problems, ICD-10) [13] and outcomes concerning live births and stillbirths with birth weight of ≥ 500 g or gestational age ≥ 22 weeks from the beginning of pregnancy until the first seven days after birth. The Finnish national data protection legislation guided study process and authorization to use the data was given by the MBR keeper, the Finnish Institute of Health and Welfare (references: THL/1749/5.05.00/2011, THL/998/5.05.00/2013 and THL/876/5.05.00/2017).

In this study setting, to analyse the busy day effect, daily delivery frequencies and ranges (min-max) were first calculated for each of the 26 delivery units and then the daily delivery volume distribution was stratified by hospitals’ annual delivery volume or profile into five categories (C1-C5). The category C1 included the smallest local and central level delivery units (n = 7) across the country with annual delivery volumes of less than 1000 deliveries. The low daily and annual delivery volumes in these small delivery units resulted in a small sample size of deliveries in C1. The limit of < 1000 annual deliveries was chosen because it is aligned with Finnish legislation. In Finland, a delivery unit should have at least 1000 annual deliveries to maintain and ensure patient safety. Hospital categories C2 (n = 10) and C3 (n = 2) included local and central level delivery units with annual delivery volumes from 1000 to 1999 and from 2000 to 2999, respectively. The hospital category C4 included two large sized central level delivery units, placed near by the capital area with ≥ 3000 annual deliveries (Table 1). University hospitals in hospital category C5 were categorised as its own category, because of the profile of tertiary level care, a country wide referral system and a different patient mix compared to large central hospitals. University hospitals are focusing on demanding cases and specialist level care in the field of obstetrics. The largest university hospital is located in the capital area and it is validated to treat the most high-risk pregnancies and deliveries and take care of the most extreme preterm deliveries across country. Some delivery units may have changed from the original hospital category during the study period, however, such changes also affect the variation and keeps the analysis consistent. The type of hospital categorisation in this study setting is in line with the Finnish organisation of delivery units and allocates an adequate number of hospitals in each hospital category to provide statistical power to the analyses.

The varying daily delivery volume periods were defined based on annual delivery volume as quiet, optimal and busy days by counting the daily delivery frequency and range (min-max) for each hospital category. Mean and range (min-max) of daily delivery volume varied between hospital categories, and each hospital category had its own definition for daily delivery volume variation. To define busy days, the number of days (%) with most high daily delivery volumes were summed to represent the closest 10 % on each hospital category. Quiet days were also defined by summing the number of days (%) with the most low delivery volume frequency days to the nearest 10 % in each the hospital category (C1─C5). Optimal days were defined with calculating around 80 % of the days between the lowest 10 % and highest 10 % daily delivery volume frequency days inside each hospital category (Table 1). Days with zero deliveries per day were not included in the calculations. Quiet days in the hospital category are represented when over resourcing of staffing may occur and busy days in the hospital category are represented when under resourcing of staffing may occur. Hospital level optimal days are represented when there are optimal staffing resources within the delivery unit.

For this study, three adverse maternal outcomes were chosen based on their prevalence in delivery units. Data availability and the results of previous literature also supported this decision. Including blood transfusions as a defined outcome was chosen as a surrogate for postpartum haemorrhage (PPH). PPH is one of the most severe maternal outcomes and is also listed as a considerable cause of maternal death during labour [14]. Definition of blood transfusions in this study includes interventions of red blood cell transfusion, thrombocytes and fresh frozen plasma during delivery or postpartum in a delivery unit. Maternal outcome is defined as MRP which also included diagnoses of a retained placenta. MRP is likely to be related to PPH and if it occurs, may need additional emergency obstetric care [15]. Maternal adverse outcome is defined as OASIS including information of third- and fourth- degree perineal tears. OASIS as widely used as a perinatal health indicator and is also associated with reflections of maternal morbidity [16, 17].

To analyse the association between varying daily delivery volume and blood transfusions, all delivery modes were included in the analysis (vaginal delivery, vacuum assisted delivery, Caesarean delivery). Covariates were chosen and categorised as maternal age, parity, birth weight and delivery mode. To analyse associations between daily delivery volume and adverse maternal outcomes defined as MRP and OASIS, only vaginal deliveries were included in the analysis. Covariates for MRP were defined as categorised maternal age, parity and birth weight. Covariates for OASIS were defined as categorised maternal age, parity, birth weight, vacuum assisted delivery. Covariates were defined based on earlier literature and categorised by delivery mode (vaginal delivery, vacuum assisted delivery, caesarean section), maternal age (< 25, 25 to 34, ≥ 35 years), parity (nulliparous, multiparous), and birth weight (< 3000 g, 3000–3999 g, ≥ 4000 g).