Dilla, Andrew J. BSc; Waters, Jonathan H. MD; Yazer, Mark H. MD
University of Pittsburgh School of Medicine, the Departments of Anesthesiology and Pathology, University of Pittsburgh, and the Institute for Transfusion Medicine, Pittsburgh, Pennsylvania.
Corresponding author: Dr. Jonathan H. Waters, MD, Department of Anesthesiology, Magee-Womens Hospital, 300 Halket Street, Suite 3510, Pittsburgh, PA 15213; e-mail: email@example.com.
Financial Disclosure The authors did not report any potential conflicts of interest.
OBJECTIVES: To determine whether the California Maternal Quality Care Collaborative risk groups predicted the risk of peripartum hemorrhage and to determine which women should have peripartum pretransfusion testing performed.
METHODS: Over a 1-year period, 10,134 women who delivered at a single hospital were included in this retrospective cohort study. The majority of the California Maternal Quality Care Collaborative risk factors were assessed retrospectively. Each mother was assigned to one of the three peripartum hemorrhage risk groups according to the guidelines. The individual peripartum hemorrhage risk factors and the three risk groups correlated with the occurrence of a significant peripartum hemorrhage (a hemorrhage requiring transfusion of 1 unit or more of red blood cells). Other risk factors for peripartum hemorrhage were assessed and a modified high-risk category was created.
RESULTS: The incidence of a significant peripartum hemorrhage within each group was as follows: low (0.8%); medium (2.0%); and high (7.3%). High included an increase that was statistically significant (P<.001). All of the assessed California Maternal Quality Care Collaborative risk criteria were significantly associated with an increased peripartum hemorrhage rate (P≤.02) except macrosomnia and morbid obesity. Other risk factors not included in the California Maternal Quality Care Collaborative criteria (preterm delivery, uterine rupture, hypertension, previous cesarean delivery, and a model of accreta or percreta) also correlated with peripartum hemorrhage. This modified risk group included 85% of those women with significant hemorrhage; however, 45% of women were included and only 2.6% of this modified group hemorrhaged.
CONCLUSION: The California Maternal Quality Care Collaborative risk stratification showed an increasing risk for transfusion as the risk grade increased. Women in the California Maternal Quality Care Collaborative high-risk group (or as determined by their providers) should have pretransfusion testing performed.
LEVEL OF EVIDENCE: II
The incidence of peripartum hemorrhage has increased over the past two decades in the United States.1,2 It is a major cause of maternal morbidity3,4 and contributes to a substantial number of maternal deaths.5 Hemorrhage is still a leading cause of maternal death and is an increasing cause of major maternal morbidity.6
To predict and to be prepared for peripartum hemorrhage, the California Maternal Quality Care Collaborative established guidelines based on known clinical and laboratory risk factors for peripartum hemorrhage.7 An important component of the guidelines is the assignment of a pregnant woman to one of three peripartum hemorrhage risk categories that is used to determine the extent of pretransfusion testing required for that patient. No pretransfusion testing is recommended for patients in the low-risk group, whereas some degree of pretransfusion testing is recommended for patients in the medium-risk or high-risk groups (Table 1).
The California Maternal Quality Care Collaborative risk categories were developed using expert opinion and have not been clinically validated to determine whether they correlate with peripartum hemorrhage. These guidelines have been widely adopted across the United States, including at Magee-Womens Hospital of University of Pittsburgh Medical Center, a regional tertiary care facility. Since implementing the guidelines in 2010, Magee-Womens Hospital of University of Pittsburgh Medical Center has performed significantly more pretransfusion testing in peripartum women. This study sought to determine whether the California Maternal Quality Care Collaborative risk groups predicted the risk of a significant peripartum hemorrhage. Other potential risk factors for peripartum hemorrhage were also evaluated and added to the California Maternal Quality Care Collaborative criteria in an attempt to increase specificity of the criteria for predicting peripartum hemorrhage.
MATERIALS AND METHODS
The purpose of this study was to correlate the California Maternal Quality Care Collaborative peripartum hemorrhage risk categories with the occurrence of a significant peripartum hemorrhage, which was defined in this study as a peripartum bleed significant enough to require the transfusion of at least 1 unit of packed red blood cells (RBCs).
Per hospital policy, when a woman presents for delivery at Magee-Womens Hospital of University of Pittsburgh Medical Center, a peripartum hemorrhage risk assessment is performed by a nurse or physician to define her California Maternal Quality Care Collaborative risk category. The woman is then assigned to the highest risk category for which she has a risk factor and the extent of pretransfusion testing as specified in the guidelines is ordered.
Information related to the prenatal peripartum hemorrhage risk, as specified in the California Maternal Quality Care Collaborative guidelines, for each woman who gave birth at Magee-Womens Hospital of University of Pittsburgh Medical Center in 2011 was captured by searching for specific International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes relevant to the risk factors. These data were collated in a spreadsheet for analysis. Basic demographic information for each woman, including her age, gravidity and parity status, and the gestational age of her fetus, was provided along with the peripartum hemorrhage risk assessment criteria or was assessed by individual chart review when necessary. Information on risk factors such as a history of a previous peripartum hemorrhage, thrombocytopenia, and active bleeding on admission were not consistently available and therefore were not used for peripartum hemorrhage risk stratification in this study.
In addition to the California Maternal Quality Care Collaborative guideline criteria, ICD-9-CM codes for several other peripartum hemorrhage risk factors including uterine rupture, cesarean delivery, antenatal hypertension, gestational age, polyhydramnios, maternal age, and Asian or Hispanic ethnicity were extracted for each woman. A model for patients with accreta or percreta was created by combining the data for women with previa or low-lying placenta with previous cesarean delivery. These nine additional risk factors were evaluated for their correlation with a significant peripartum hemorrhage. A modified California Maternal Quality Care Collaborative high-risk group then was created by moving the patients who had any of these additional risk factors that were significantly correlated with a peripartum hemorrhage into the high-risk group, if they had not already been classified as high-risk by the original California Maternal Quality Care Collaborative criteria.
A list of all women who received at least 1 unit of RBCs during 2011 was generated from the electronic records of the Magee-Womens Hospital of University of Pittsburgh Medical Center transfusion service, and it was merged with the list of all women who gave birth in 2011 to determine which women experienced a significant peripartum hemorrhage. Using the list of women who underwent transfusion from the records of the blood bank ensured that even if a woman had a significant peripartum hemorrhage but was not assigned the appropriate ICD-9-CM code for peripartum hemorrhage, she still would have been included in this study.
Continuous variables were analyzed using descriptive statistics, categorical variables were analyzed using χ2, and the relative risk of having a significant peripartum hemorrhage was calculated using GraphPad Prism version 6. This protocol was approved by the University of Pittsburgh Total Quality Council, a division of the Institutional Review Board.
In 2011, there were 10,134 women who gave birth at Magee-Womens Hospital of University of Pittsburgh Medical Center. The demographic characteristics of these women varied significantly between the three risk groups, with a larger proportion of primiparous women in the low-risk group (Table 2). Overall, a peripartum hemorrhage that was significant enough to require the transfusion of at least 1 unit of RBCs occurred in 139 women (1.4%). There was a significant increase in the rate of peripartum hemorrhage as the risk groups increased in severity (P<.001). The rates of peripartum hemorrhage within each risk group were as follows: low (0.8%); medium (2.0%); and high (7.3%) (Table 3). Of the 139 women with peripartum hemorrhage, 22% were classified in the high-risk category. In all three risk groups, the patients who required an RBC transfusion received a median of 2 units (range 1–22 units).
All of the evaluated California Maternal Quality Care Collaborative risk factors for peripartum hemorrhage were associated with a significantly increased relative risk of experiencing a significant peripartum hemorrhage (P≤.02 for all parameters that were significantly associated with peripartum hemorrhage), except for the criteria of macrosomia and morbid obesity, which were not significantly associated with peripartum hemorrhage (Table 4).
The additional factors that were associated with a significantly increased risk of peripartum hemorrhage but that were not included in the original California Maternal Quality Care Collaborative criteria were cesarean delivery, antenatal hypertension, uterine rupture, preterm delivery (less than 37 weeks of gestation), and a model for accreta or percreta (P<.001 for these parameters) (Table 4). By reclassifying the patients with any of these five factors as high risk, the new modified high-risk group contained 85% of all of the women who experienced a significant peripartum hemorrhage; the percentage of women who had a significant peripartum hemorrhage in this new high-risk category was 2.6% (Table 5).
Using the California Maternal Quality Care Collaborative risk stratification guidelines, a statistically significant difference in significant peripartum hemorrhage rates was observed between women in the low-risk, medium-risk, and high-risk groups. The clinical significance of this finding is uncertain given that the majority of women, even in the high-risk group, did not require peripartum RBC transfusions. It is difficult to justify performance of a type and screen in the women in the medium-risk group because only 2% of those women had a significant peripartum hemorrhage. Thus, 98% of the type and screens that were performed in these women never resulted in an RBC transfusion and unnecessarily increased the hospital charges for the patients while occupying nursing and transfusion service resources. A type and screen takes approximately 45 minutes to perform once it has been received by the transfusion service. If the woman has not become alloimmunized to RBCs, cross-matched RBCs can be available within 5 minutes using an electronic cross-match system, which is commonplace in most large hospitals; it would take another 30–40 minutes for hospitals that do not use this system. Thus, cross-matched RBCs can be readily available after the type and screen sample is obtained in the blood bank in the unlikely event that women in the low-risk or medium-risk categories require a transfusion. A recent study recommended performing a type and screen only if the expected transfusion rate is 5.0% or higher.8 Similarly, the women in the high-risk category had a significant peripartum hemorrhage rate of 7.3%, which does not warrant the cross-matching of 2 units of RBCs for each woman; a type and screen alone for women in this category would suffice. For women who have become alloimmunized, the recommendations for the extent of pretransfusion testing should include not only the clinical criteria discussed herein but also the number and complexity of the antibodies. Regardless of the assigned risk category, the physician's clinical judgment and case-by-case assessment of the patient's propensity for peripartum hemorrhage, as well as peripartum hemorrhage risk factors that develop as the delivery progresses, should guide the extent of pretransfusion testing ordered. In addition, although not evaluated in this study, other risk factors for peripartum hemorrhage such as significant thrombocytopenia, bleeding on admission, and a history of peripartum hemorrhage also should be considered when deciding on the appropriate extent of pretransfusion testing to be performed on each patient.
If a large and unexpected peripartum hemorrhage occurs in a woman who did not have a type and screen sample drawn before delivery, then uncross-matched RBCs should be rapidly available from the blood bank (less than 5 minutes from the time they are ordered). Uncross-matched RBCs are always group O and thus are compatible with any recipient. The absence of hemolysis or other adverse events after the use of uncross-matched RBCs has been previously demonstrated.9–11 Uncross-matched RBCs do not confer a higher risk of anti-RBC sensitization compared with cross-matched RBCs because neither of these units are matched for the recipient's minor antigens. Thus, the absence of completed pretransfusion testing before delivery should not cause a delay in providing RBCs when they are urgently required.
In other retrospective studies of the risk factors of peripartum hemorrhage, the methods of defining hemorrhage were variable.12–17 Some studies used RBC transfusions as an endpoint but many relied on visually estimated blood loss to define a significant hemorrhage. The latter technique can be inaccurate18,19 and may have contributed to the inconsistent results between these previous retrospective studies. Our study used RBC transfusion as the indicator of a significant hemorrhage because the California Maternal Quality Care Collaborative guidelines recommend varying levels of pretransfusion testing depending on the patient's risk of hemorrhage.
In our modified peripartum hemorrhage risk assessment (Table 5), the high-risk group captured the majority (85%) of women who had a significant peripartum hemorrhage. However, the clinical value of this alternative risk stratification is low because of the low peripartum hemorrhage rate in the high-risk category (2.6%) and the similar relative risks of peripartum hemorrhage between women in the high-risk groups of both the current California Maternal Quality Care Collaborative guidelines and our modified high-risk group (6.50 compared with 6.94, respectively). Even though the modified high-risk category was created by adding women who had other clinical criteria that were statistically correlated with peripartum hemorrhage to the original California Maternal Quality Care Collaborative high-risk group, the percentage of patients within this group who experienced a peripartum hemorrhage was actually lower than that of the original high-risk group. This is because 10-times more women would have been classified as high risk using the modified guidelines; thus, the increased sensitivity of these modified guidelines is offset by a reduction in their specificity compared with the original California Maternal Quality Care Collaborative guidelines. More research is needed to elucidate the factors that predict peripartum hemorrhage so that effective recommendations for pretransfusion testing in this patient population can be made.
The main limitation of this study is that because some of the California Maternal Quality Care Collaborative criteria were derived from the patient's history or from situations for which an ICD-9-CM code does not exist, we could not reliably establish whether the patient had experienced those risk factors using our strategy of gathering clinical information based on ICD-9-CM codes. Perhaps if we had been able to ascertain the presence of these risk factors in our cohort of women, we would have had higher rates of significant peripartum hemorrhage in the medium-risk and high-risk groups. Given that admission hematocrit less than 30% is a high-risk criteria in the California Maternal Quality Care Collaborative guidelines, it is also possible that some women who were severely anemic before their delivery received an RBC transfusion for what otherwise would have been a minor amount of blood loss; in this population, a significant peripartum hemorrhage that stimulated a transfusion likely would have been of a smaller volume than in a nonanemic patient.
Because of the low incidence of severe peripartum hemorrhage in our data set, it does not seem necessary to obtain a specimen for pretransfusion testing in women in the low-risk and medium-risk California Maternal Quality Care Collaborative groups, although women in the high-risk group should have a type and screen performed when they are admitted for delivery. However, the attending physician's assessment of each patient is also an important factor in determining when pretransfusion testing should be performed.
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