Audits of maternal mortality are important measures of the quality of obstetric care.1,2 This event, however, is rare in wealthy nations.3,4 Measures of “near-miss” maternal mortalities, a more common occurrence, may provide more meaningful information regarding determinants of severe obstetric morbidity as well as trends in management and outcome.5,6 Near-miss maternal mortalities represent events that would have resulted in a maternal death during pregnancy and childbirth if not for significant medical intervention.7 Unfortunately, definitions of near-miss maternal mortality vary across institutions and among nations.8–10 Despite these variations in definitions, a commonly accepted measure of near-miss maternal mortality is intensive care unit (ICU) admission.6,11–15
Obstetric ICU admissions are rare with rates of 0.5–7.6 per 1,000 births.11 Most retrospective, observational studies demonstrate ICU near-miss morbidities that parallel known causes of maternal mortality: hemorrhage, sepsis, and maternal hypertensive disease. Demographic changes in the U.S. obstetric population, with increasing rates of cesarean delivery, obesity, and advanced maternal age, may lead to higher maternal morbidity and affect changes in obstetric ICU admissions.
Many social and economic factors are associated with severe maternal morbidity and mortality. African American women demonstrate a fourfold higher maternal mortality ratio than white women in the United States.16 Analyses of near-miss maternal morbidity are varied; however, maternal race and ethnicity are associated with disparities in outcome.17 Studies from Europe, Australia, and New Zealand demonstrate higher rates of obstetric ICU admissions and maternal deaths for immigrant and nonwhite populations.14,18–20 Similarly, in the United States, when race and ethnicity are specified, many authors describe higher percentages of African American obstetric admissions to ICUs than expected based on population demographics.21,22 Few studies analyze obstetric ICU admission diagnoses and determinants of potential disparities by race and ethnicity.
The primary objective of this study was to examine the demographic, medical, and pregnancy-related variables associated with maternal ICU admissions and near-miss maternal morbidities. A secondary objective was to determine the pregnancy outcomes of women experiencing near-miss mortalities to learn more about the interventions necessary to avert a maternal death.
MATERIALS AND METHODS
Pregnant and postpartum patients admitted to Duke University Medical Center's surgical, medical, cardiac, pulmonary, and neurology ICUs from January 2005 to April 2011 were included in the study. The labor and delivery unit at our institution is a high-dependency center where most severe maternal morbidities, including eclampsia, postpartum hemorrhage, and pulmonary embolism, are managed. However, women requiring prolonged ventilator support, in unstable condition, or both, predelivery or postpartum, are transferred from labor and delivery to the ICUs.
A trained study coordinator identified and approached all obstetric patients admitted to the ICUs and offered inclusion in our obstetric ICU registry. Enrolled women agreed to participate either directly or indirectly through consent granted by family members or designated proxies. Maternal demographic data recorded included age, parity, body mass index (BMI, calculated as weight (kg)/[height (m)]2), race and ethnicity, primary language, insurance status, employment status, marital status, city and county of origin, and receipt of prenatal care.
Clinical data obtained from review of maternal records and bedside observation included primary indication for ICU admission, antepartum, postpartum, or both status at the time of ICU admission, comorbid medical conditions, therapeutic interventions such as blood transfusion or intubation, and length of ICU and hospital stay. Neonatal outcomes such as birth weight, neonatal ICU admission, length of hospital stay, and survival also were recorded.
Investigators (A.J. and M.S.) reviewed all records and verified the primary admission diagnoses leading to ICU stay, because some patients had multiple, concomitant severe comorbidities. Statistical analysis was performed with SPSS. Differences between racial groups were tested for significance with the chi-square test and analysis of variance for categorical and continuous variables, respectively. The 95% confidence intervals were calculated with P set at <.05. The Duke University School of Medicine institutional review board approved this study.
During the study period, 19,575 births occurred. There were five maternal deaths: two resulted from metastatic cancer, two secondary to cystic fibrosis, and one the result of sepsis. Ninety-four obstetric patients—five per 1,000 deliveries—were admitted to ICUs. Eight declined participation in the study. Eighty-six patients were included in this analysis.
Table 1 shows a comparison of demographic characteristics by race and ethnicity. African American women comprised the largest population admitted to the ICU (45%). Significant differences were found by race and ethnicity in the following variables: parity, BMI, and marital and insurance status. African American (mean 35) and Hispanic women (mean 36) had significantly higher BMIs than white women (mean 28). African American and Hispanic women were also more likely to have Medicaid or no insurance and were more likely to be unmarried and multiparous. No significant differences in admission diagnosis, maternal medical comorbidities, or neonatal outcome were noted based on maternal race and ethnicity or maternal BMI (data not shown). The majority (87%) of patients transferred to the ICUs were admitted postpartum (Table 2).
Table 3 demonstrates the principal cause for ICU admission. The leading admission diagnosis for pregnant and postpartum women was maternal cardiac disease (36%). Maternal hemorrhage (both obstetric and nonobstetric) was the second leading reason for admission (29%). Hypertensive disease accounted for 9% of ICU admissions. Of note, the overall rate postpartum hemorrhage previously reported at our institution is 5.4%, whereas preeclampsia and eclampsia complicate approximately 7–10% of all pregnancies.23
The majority of cardiac conditions prompting ICU admission resulted from cardiomyopathy. Acute complications associated with peripartum cardiomyopathy comprised the majority of this group. Congenital heart disease is the underlying etiology for many of these valvular lesions and cardiomyopathies. Congenitally acquired conditions were the second leading cause of maternal cardiac ICU admissions (Table 4).
The majority of women admitted to ICUs had known, severe cardiac disease with complications or developed acute cardiac events during pregnancy. The hemodynamic shifts associated with labor, delivery, and the puerperium place women with known cardiac disease at higher risk for maternal mortality. Intensive care management potentially averts maternal death.24
Cardiomyopathy is the leading cause of maternal mortality in North Carolina.25 Aggressive identification and management of patients with known or suspected cardiomyopathy are associated with reduced maternal mortality in our population.24 An additional contributor to maternal ICU admissions for cardiac conditions is related to the fact that our facility is a tertiary care referral center for women with congenital heart disease. Women with critical cardiac conditions, requiring advanced interventions, can be effectively managed using a multidisciplinary approach.
Similar to other studies, African American women comprised the majority of patients admitted to the ICUs.21,22 These findings are consistent with the literature both in the U.S. and in European populations. In The Netherlands, ethnic minorities were more likely to experience near-miss maternal deaths.14,26 In the U.K. confidential inquiries into maternal mortality, similar increases in maternal mortality were identified among immigrants and ethnic minorities.2 Previous work from our institution demonstrated ethnic differences in maternal mortality and morbidity with African American women demonstrating higher rates of chronic disease and maternal mortality but Hispanic women demonstrating higher rates of near-miss maternal mortality.17 The reasons for these differences are multifactorial and likely the result of socioeconomic factors (eg, language barriers, medical knowledge, quality of care) as well as medical comorbidities.26,27
Maternal obesity is an established risk factor for severe obstetric morbidity and mortality. Unfortunately, most studies of obstetric ICU admissions do not include measures of maternal weight or BMI; therefore, it is difficult to compare across populations or assess differences over time. In the U.K. Confidential Enquiry into Maternal and Child Health, overweight and obesity were associated with approximately 50% of maternal deaths.2 Sixty-one percent of maternal cardiac deaths were associated with overweight and obesity.2 Disparities in maternal obesity for African American and Hispanic women were observed in our study; however, these differences in BMI did not affect other maternal medical comorbidities or outcomes.
Cardiovascular disease in pregnancy is on the rise globally as a leading cause of maternal morbidity and mortality.2,28–31 The role of race and ethnicity as an independent contributor to these outcomes is not clear. In a national population-based sample, James et al28 demonstrate an increase in myocardial infarction rates for African American women; however, in multivariable models adjusting for risk factors such as smoking status, diabetes mellitus, obesity, and physical inactivity, race was not found to be an independent predictor of myocardial infarction.
The limitations of this study are the small sample size. The size, however, is comparable to other single-center reports in the literature. Intensive care unit admissions are not cumbersome to identify and track as a measure of obstetric morbidity; however, criteria for ICU admission does vary across institutions. Although the small sample may limit rigorous evaluation of the factors contributing to disparities in severe adverse outcomes, the multiethnic nature of our population does allow for assessment of racial and ethnic differences in ICU admissions. The prospective study design is unique because there are few such studies in the literature.8,32–34
In general, ICU admissions represent approximately one-third of severe obstetric morbidities.15 Mahutte et al13recommend using unplanned ICU admissions as quality assessment indicators for obstetric care. They suggest maternal morbidities are separate from and different from maternal mortalities. We observed a similar finding. In our population, 40% of maternal deaths resulted from metastatic cancer and none occurred in the context of the most common causes of maternal ICU admission: cardiac conditions, hemorrhage, or preeclampsia. As a tertiary care center, our facility has a similar numbers of transfers (23%) from outside hospitals.13,35 Assessment of these severe morbidities may allow for evaluation of adequate obstetric care. Such an analysis can enable health care providers and institutions to assess performance according to established standards or protocols.8,13,36 Regular scrutiny of ICU admissions is a valuable and manageable means of surveillance for near-miss maternal mortality.
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