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Contents: Original Research

Severe Maternal Morbidity Among Hispanic Women in New York City

Investigation of Health Disparities

Howell, Elizabeth A. MD, MPP; Egorova, Natalia N. PhD, MPH; Janevic, Teresa PhD, MPH; Balbierz, Amy MPH; Zeitlin, Jennifer DSc, MA; Hebert, Paul L. PhD

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doi: 10.1097/AOG.0000000000001864
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Racial and ethnic disparities in maternal morbidity and mortality exist, although the reasons for these gaps are not fully understood.1,2 Growing attention has focused on location of care as a partial explanation for these disparities.3 In our recent work, we found that non-Hispanic black women deliver at higher risk-adjusted severe maternal morbidity hospitals.4 Hispanic women in New York City are three times more likely than non-Hispanic white women to experience pregnancy-related mortality, yet few studies have examined how site of care might contribute to these disparities.1 Furthermore, few studies have investigated how maternal risk varies among Hispanic subgroups and the interplay of this risk with site of delivery. Our objectives were to examine differences in severe maternal morbidity between Hispanic women and three major Hispanic subgroups compared with non-Hispanic white women and to examine whether these differences are explained by delivery hospital.

MATERIALS AND METHODS

We conducted a population-based cross-sectional study using Vital Statistics birth records linked with New York State discharge abstract data, The Statewide Planning and Research Cooperative System, for all delivery hospitalizations in New York City from 2011 to 2013. Data linkage was conducted by the New York State Department of Health and institutional review board approval was obtained from the New York City Department of Health and Mental Hygiene, the New York State Department of Health, and the Icahn School of Medicine at Mount Sinai. Delivery hospitalizations were identified based on International Classification of Diseases, 9th Revision, Clinical Modification diagnosis and procedure codes and diagnosis-related group delivery codes.5 More than 98% of maternal discharges were linked with infant birth certificates. The final sample included 353,773 total deliveries of live neonates at 40 hospitals.

Hispanic ethnic ancestry was obtained by self-report from the birth certificate. We were able in our data set to identify three Hispanic subgroups based on the Hispanic categories included in the question on the New York City birth certificate: foreign-born Dominican, foreign-born Mexican, and Puerto Rican. Race was obtained by self-report from the birth certificate. Maternal race and Hispanic ethnicity in birth certificate data have been shown to have high sensitivity and specificity.6 This article compares severe maternal morbidity among Hispanic mothers of any racial group compared with non-Hispanic white mothers in New York City.

We used a published algorithm to identify severe maternal morbidity using diagnoses for life-threatening conditions and procedure codes for life-saving procedures defined by investigators from the Centers for Disease Control and Prevention7,8 (see Appendix 1, available online at http://links.lww.com/AOG/A914). We risk-adjusted hospital-level rates of maternal morbidity using mothers' sociodemographic characteristics (eg, self-identified race and ethnicity, age, country of birth) and clinical and obstetric factors (eg, multiple pregnancy, history of previous cesarean delivery, body mass index, prenatal care). Similar to others, we also adjusted for clinical comorbidities (eg, diabetes, hypertension, prelabor rupture of membranes, disorders of placentation).9–12

Teaching status was obtained from the American Hospital Association, ownership and nursery level from the New York State Department of Health, and volume of deliveries in each hospital from The Statewide Planning and Research Cooperative System.

We compared sociodemographic characteristics and clinical conditions of Hispanic women overall and for the three major subgroups with those of non-Hispanic white women, using χ2 tests. Because our focus was to examine the three most prevalent Hispanic subgroups in New York City, we did not conduct subgroup analyses on the remaining group of other Hispanic women (n=41,091). This group was comprised of foreign-born and U.S.-born Hispanic women from Caribbean and Central and South American countries. We then compared severe maternal morbidity rates across these groups using logistic regression to adjust for the differences in maternal sociodemographic and clinical covariates and, also, in a second model, for hospital fixed effects. Robust standard errors were used to account for clustering in hospitals.

To evaluate variability between hospitals, we used mixed-effects logistic regression with the same patient characteristics and a random, hospital-specific intercept to generate risk-standardized severe maternal morbidity rates for each hospital using methods recommended by Hospital Care (https://www.medicare.gov/hospitalcompare/search.html?).12,13 These analyses included women of all racial and ethnic groups who delivered in New York City.12,13 These rates were the ratio of predicted-to-expected severe maternal morbidity rates multiplied by the New York City average severe maternal morbidity rate.12 For each hospital, the numerator of the ratio is the number of severe maternal morbidity cases predicted on the basis of the hospital's performance with its case mix and the denominator is the number of severe maternal morbidity cases expected on the basis of the New York City performance with that hospital's case mix. These models use empirical Bayesian methods that “shrink” estimates from small hospitals, which tend to be outliers in statistical models, toward the mean hospital outcome.14 We ranked hospitals from lowest to highest risk-standardized severe maternal morbidity rates. These analyses did not include hospital-level variables,12 because doing so could distort the ranking of hospitals. Because blood transfusions account for a significant proportion of severe maternal morbidity events, we conducted three sensitivity analyses. First, given that isolated blood transfusions do not include information on number of units transfused and therefore may not be reflective of severe events, we examined whether isolated blood transfusions in this cohort were associated with excess risk (eg, placentation disorders, hypertension, and other comorbidities) using a multivariable logistic model. Second, we examined the correlation between hospital rankings based on risk-standardized severe maternal morbidity with and without blood transfusion. Third, we examined risk of severe maternal morbidity without blood transfusion for Hispanic and white women and confirmed that Hispanic women had an elevated risk-adjusted severe maternal morbidity rate when isolated blood transfusions were removed from the index after taking into consideration patient and clinical comorbidities.

To assess ethnic disparities in the use of hospitals with the lowest morbidity rates, we calculated the cumulative distributions of births among hospitals ranked from the lowest to the highest standardized morbidity rate for Hispanic mothers overall and for the three major ethnic groups compared with white mothers. We used the Kolmogorov-Smirnov test to assess whether the distributions of deliveries among hospitals differed for white and Hispanic women.15 We also compared the distribution of Hispanic mothers overall and for the three major ethnic groups compared with non-Hispanic white deliveries in the lowest morbidity tertile of hospitals using χ2 tests.

These statistical analyses assess whether Hispanic mothers are systematically receiving care at lower quality hospitals but do not provide a measure of the magnitude of the consequences for Hispanic mothers' health of receiving lower quality care. To address the magnitude, we conducted a simulation and asked what would happen if Hispanic women went to the same hospitals as non-Hispanic white women. This methodology has been previously described.4,16 We used the same risk-standardized morbidity model and kept all individual patient characteristics the same. We calculated the predicted probability of morbidity for each Hispanic mother at each hospital. For each Hispanic mother, we took the weighted average of these probabilities, in which weights were the percentage of non-Hispanic white mothers who went to each hospital. The difference between the predicted probability at the hospital a Hispanic mother went to and the weighted average probability if the Hispanic mother delivered at the non-Hispanic white mother's hospital is the decrease or increase in the probability of a morbid event. The sum of the difference in probabilities across all Hispanic women is the morbid events avoided if Hispanic mothers went to the same hospitals as white mothers.4,16 We conducted similar simulations for mothers in the three Hispanic subgroups such that each foreign-born Dominican, foreign-born Mexican, and Puerto Rican mothers went to the same hospitals as non-Hispanic white women.

Next we examined the potential effect on disparities between Hispanic and non-Hispanic white morbidity rates of improving quality in low-performing hospitals. We estimated the effect of lowering severe maternal morbidity rates in the highest morbidity tertile of hospitals to the average of the remaining hospitals. We did this by estimating a logistic model with maternal characteristics and a single dummy variable for whether the delivery hospital was in the highest morbidity tertile, setting this dummy variable equal to zero for all mothers, and calculating the predicted morbid events. We also estimated the effect of a reduction in severe maternal morbidity rates of the middle and highest morbidity tertiles of hospitals to the average of the remaining hospitals using similar methods.

All statistical analysis was performed using SAS 9.4.

RESULTS

Hispanic mothers accounted for 29.9% and white mothers for 31.1% of the 353,773 deliveries in New York City in 2011–2013. Hispanic women were more likely to be younger, born outside of the United States, obese, have Medicaid insurance, and more likely to experience a number of comorbidities, including hypertension, diabetes, and asthma (Table 1).

Table 1.
Table 1.:
Sociodemographic, Clinical, and Hospital Characteristics of Deliveries for Hispanic Women and Non-Hispanic White Women in New York City Hospitals
Table 1-A.
Table 1-A.:
Sociodemographic, Clinical, and Hospital Characteristics of Deliveries for Hispanic Women and Non-Hispanic White Women in New York City Hospitals

Maternal sociodemographic and clinical characteristics also differed significantly among the three Hispanic subgroups (Table 2). Puerto Rican women were younger and were more likely to have private insurance than those who were foreign-born Mexican or Dominican. Foreign-born Mexican mothers were half as likely as either Puerto Rican or foreign-born Dominican mothers to have a high school education. All three Hispanic subgroups had elevated rates of hypertension and gestational diabetes, and Mexican women had the highest rates of gestational diabetes mellitus. Puerto Rican women had higher rates of obesity and asthma than Mexican and Dominican women.

Table 2.
Table 2.:
Sociodemographic and Clinical Characteristics of Deliveries by Hispanic Subgroup in New York City Hospitals

Severe maternal morbidity occurred in 4,541 deliveries, and rates were higher among Hispanic (2.7%) as compared with non-Hispanic white (1.5%) mothers (P<.001; Table 3). Rates of severe maternal morbidity were even higher among the three subgroups of Hispanic women (2.9% among Puerto Rican, 2.7% among foreign-born Dominican, 3.3% among foreign-born Mexican). These differences remained in adjusted models, but the odds ratio (OR) decreased from 1.87 (95% confidence interval [CI] 1.76–1.99) to 1.42 (95% CI 1.22–1.66) for Hispanic compared with non-Hispanic white women after accounting for other maternal sociodemographic and clinical factors. Odds ratios were reduced further after accounting for site of delivery (OR 1.26, 95%CI 1.18–1.42). Risks were elevated among the three major Hispanic subgroups with the highest odds for morbid events among foreign-born Mexican women.

Table 3.
Table 3.:
Association Between Hispanic Ethnicity and Severe Maternal Morbidity

Of the 40 hospitals, 11 were public, 33 had level III or IV nurseries, and 39 were teaching hospitals. The median percentage of Hispanic deliveries was 28.7 (interquartile range 17.1–54.2%, minimum 6.8%, maximum 89.5%). Observed severe morbidity rates for hospitals ranged from 0.6% to 11.5% and risk-standardized rates using a model including maternal sociodemographic and clinical characteristics from 0.8% to 5.7% (Fig. 1). The risk-standardized morbidity rate for the highest mortality tertile of hospitals was 3.8% and 1.5% for the lowest (P<.001). Isolated blood transfusions accounted for 67% of severe morbid events. Sensitivity analyses confirmed that isolated blood transfusions were a marker of excess risk and were strongly associated with placentation disorders, hypertension, pregnancy-induced hypertension, previous cesarean delivery, and a number of other comorbidities. In addition, sensitivity analyses demonstrated that hospital rankings based on the Centers for Disease Control and Prevention severe maternal morbidity algorithm with and without blood transfusion were highly correlated (Spearman ρ=0.67, P<.001) and confirmed that Hispanic compared with non-Hispanic white women had an elevated but attenuated risk-adjusted severe maternal morbidity rate when isolated blood transfusions were removed from the index (OR 1.17, 95% CI 1.02–1.33).

Fig. 1.
Fig. 1.:
Observed and risk standardized severe maternal morbidity rates (SSMMRs) in New York City hospitals. Dotted line shows New York City mean observed severe maternal morbidity. The 95% confidence interval for risk SSMMR is shown. Reprinted from Howell EA, Egorova NN, Balbierz B, Zeitlin J, Hebert PL. Site of delivery contribution to black-white severe maternal morbidity disparity. Am J Obstet Gynecol 2016;215:143–52. Copyright 2016, with permission from Elsevier.Howell. Delivery Hospital and Hispanic Maternal Morbidity. Obstet Gynecol 2017.

The cumulative distribution of deliveries among hospitals ranked from lowest to highest morbidity rates differed for Hispanic and non-Hispanic white mothers (P=.003; Fig. 2). The majority of non-Hispanic white deliveries (65.3%) occurred in the hospitals in the lowest tertile for severe morbidity compared with 33.0% of all Hispanic deliveries; 29.0% Puerto Rican, 34.4% Dominican, and 23.8% of Mexican women delivered in those same hospitals.

Fig. 2.
Fig. 2.:
Cumulative distributions of deliveries according to hospital, ranked from lowest (1) to highest (40) morbidity ratio. A. Hispanic and non-Hispanic white mothers. B. Mexican, Puerto Rican, Dominican, and non-Hispanic white mothers.Howell. Delivery Hospital and Hispanic Maternal Morbidity. Obstet Gynecol 2017.

If Hispanic mothers delivered in the same hospitals as non-Hispanic white women, our simulation model estimated that they would experience 485 fewer severe morbid events, leading to a reduction of the Hispanic severe maternal morbidity rate from 2.74% to 2.28%, removing 36.5% of the Hispanic–white disparity in severe maternal morbidity (Table 4). By ethnic subgroup, Puerto Rican women would experience 131 fewer severe morbid events, foreign Mexican women would experience 93 fewer events, and foreign Dominican women would experience 114 fewer events.

Table 4.
Table 4.:
Effects of Ethnic Differences in Distribution of Deliveries on Severe Maternal Morbidity and Effect of Improving Quality at Low-Performing Hospitals on Ethnic Disparities in Severe Maternal Morbidity Rates
Table 4-A.
Table 4-A.:
Effects of Ethnic Differences in Distribution of Deliveries on Severe Maternal Morbidity and Effect of Improving Quality at Low-Performing Hospitals on Ethnic Disparities in Severe Maternal Morbidity Rates

If quality of care were improved in New York City hospitals such that morbidity in the worse performing hospitals was reduced to the average of other New York City hospitals, 306 Hispanic and 145 non-Hispanic white severe morbid events could be averted and the Hispanic–white disparity would be narrowed by 13%. If the severe maternal morbidity rates of the middle and highest morbidity tertiles of hospitals were reduced to the average of the remaining hospitals, 1,139 Hispanic and 446 non-Hispanic white morbid events could be avoided and the Hispanic–white disparity would be narrowed by 54%.

DISCUSSION

Hispanic women in New York City deliver in higher risk-adjusted severe maternal morbidity hospitals than non-Hispanic white women, and these differences in site of care may contribute to Hispanic–non-Hispanic white disparities. All three ethnic subgroups, Puerto Rican, foreign-born Mexican, and foreign-born Dominican, had elevated rates of severe maternal morbidity and delivered in higher risk-adjusted severe maternal morbidity hospitals than non-Hispanic white women. Our findings suggest that site of delivery matters and that differences in quality of care may contribute to Hispanic–non-Hispanic white disparities. Our results raise the hypothesis that quality improvement efforts at high maternal morbidity hospitals could result in reductions in maternal morbidity overall and in Hispanic–white disparities. Our results also document the excess comorbidities of Hispanic women.

Our findings are consistent with previous literature demonstrating black–white disparities in severe maternal morbidity in New York City and the United States.3,4 Minorities deliver in a concentrated set of hospitals and these hospitals have higher rates of severe maternal morbidity and lower quality. Similar findings have been documented in other clinical areas.17,18 Given that more than one third of maternal deaths and severe morbid events are considered preventable,19 there have been major efforts by the American College of Obstetricians and Gynecologists District II, the Alliance for Innovation in Maternal Health (AIM Program), Merck for Mothers, and the New York State Department of Health to standardize care on labor and delivery units and enhance quality.20–24 Our data highlight the need for these quality improvement efforts because wide variation in risk-adjusted morbidity rates exists across hospitals. Research studies investigating organizational, structural, and process-related hospital characteristics as well as physician practice patterns that are associated with high performance in maternity care are needed.

Our findings are consistent with previous studies documenting significant racial and ethnic disparities in maternal morbidity even after adjustment for sociodemographic and clinical factors and suggest that specifically targeted quality improvement efforts to reduce disparities in maternal outcomes are needed. One such effort under development is the Alliance for Innovation in Maternal Health Reduction of Peripartum Racial/Ethnic Disparities Patient Safety Bundle, which aims to reduce racial and ethnic disparities in maternal morbidity and mortality across the United States.24 Data from other areas of medicine suggest that multifactorial tailored interventions can reduce disparities and improve health outcomes.25

Our data highlight a paradox: although perinatal outcomes are often better among Hispanic women, our results as well as data from others suggest that rates of adverse maternal outcomes are often higher among these women.26 Foreign-born Mexican women in New York City have neonatal mortality rates that are lower than non-Hispanic white women, yet our data demonstrate that foreign-born Mexican women have the highest adjusted risks of severe maternal morbidity.27 Our findings suggest that the balance of relative disadvantage and advantage experienced by Hispanic women that results in a lower risk of adverse birth outcomes may be different for maternal health outcomes such that the balance is tipped toward disadvantage. Our data also demonstrate the importance of examining subgroups of Hispanic women to better understand risk and protective factors.

Our analysis has limitations. For assessment of severe maternal morbidity, we used administrative data (International Classification of Diseases, 9th Revision procedure and diagnosis codes) that do not contain important clinical data on severity of illness, and the composite measure we used relies heavily on blood transfusions. Nevertheless, the published algorithm we used to identify severe maternal morbidity has been validated and our sensitivity analyses after removing isolated blood transfusions confirmed our findings.28 Risk for Hispanic women was attenuated when isolated blood transfusions were removed from the morbidity composite. The birth certificate has only moderate reliability for behavioral risk factors and medical events.29 We used a simulation model and estimated the extent to which differences in the distribution of deliveries may contribute to disparities but were unable to account for unmeasured factors that are associated with both ethnicity and severe maternal morbidity. The strengths are that we conducted a population-based study and were able to construct a robust risk adjustment model that included important confounders available in our linked data set (eg, education, body mass index).

New York City has elevated rates of morbidity and mortality among Hispanic women. Given that Hispanic mothers account for more than one third of all births in New York City and are the fastest growing minority in the country, research investigating the clinical characteristics and patterns of care among Hispanic women is an important step toward targeting interventions to reduce these disparities. New York City and the nation are becoming increasingly diverse, and our findings demonstrate that many ethnic women deliver their newborns in institutions with worse outcomes. Policymakers need to understand the challenges of delivering high-quality obstetric care at these hospitals and find ways to improve it.

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