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Site of delivery contribution to black-white severe maternal morbidity disparity

      Background

      The black-white maternal mortality disparity is the largest disparity among all conventional population perinatal health measures, and the mortality gap between black and white women in New York City has nearly doubled in recent years. For every maternal death, 100 women experience severe maternal morbidity, a life-threatening diagnosis, or undergo a life-saving procedure during their delivery hospitalization. Like maternal mortality, severe maternal morbidity is more common among black than white women. A significant portion of maternal morbidity and mortality is preventable, making quality of care in hospitals a critical lever for improving outcomes. Hospital variation in risk-adjusted severe maternal morbidity rates exists. The extent to which variation in hospital performance on severe maternal morbidity rates contributes to black-white disparities in New York City hospitals has not been studied.

      Objective

      We examined the extent to which black-white differences in severe maternal morbidity rates in New York City hospitals can be explained by differences in the hospitals in which black and white women deliver.

      Study Design

      We conducted a population-based study using linked 2011–2013 New York City discharge and birth certificate datasets (n = 353,773 deliveries) to examine black-white differences in severe maternal morbidity rates in New York City hospitals. A mixed-effects logistic regression with a random hospital-specific intercept was used to generate risk-standardized severe maternal morbidity rates for each hospital (n = 40). We then assessed differences in the distributions of black and white deliveries among these hospitals.

      Results

      Severe maternal morbidity occurred in 8882 deliveries (2.5%) and was higher among black than white women (4.2% vs 1.5%, P < .001). After adjustment for patient characteristics and comorbidities, the risk remained elevated for black women (odds ratio, 2.02; 95% confidence interval, 1.89–2.17). Risk-standardized severe maternal morbidity rates among New York City hospitals ranged from 0.8 to 5.7 per 100 deliveries. White deliveries were more likely to be delivered in low-morbidity hospitals: 65% of white vs 23% of black deliveries occurred in hospitals in the lowest tertile for morbidity. We estimated that black-white differences in delivery location may contribute as much as 47.7% of the racial disparity in severe maternal morbidity rates in New York City.

      Conclusion

      Black mothers are more likely to deliver at higher risk-standardized severe maternal morbidity hospitals than are white mothers, contributing to black-white disparities. More research is needed to understand the attributes of high-performing hospitals and to share best practices among hospitals.

      Key words

      Related editorial, page 140.
      Black women are 12 times more likely to suffer a pregnancy-related death than are white women in New York City.
      New York City Department of Health and Mental Hygiene
      Bureau of Maternal and Child Health. Pregnancy-associated mortality, New York City, 2006–2010.
      This disparity is 3-4 times greater than the US black-white maternal mortality disparity.
      • Callaghan W.M.
      Overview of maternal mortality in the United States.
      Not only are there striking racial disparities in maternal mortality rates, but overall performance on the maternal mortality ratio, the number of maternal deaths per 100,000 live births, in the United States is poor compared with other countries: we rank 60th among World Health Organization member nations.

      Kassebaum NJ, Bertozzi-Villa A, Coggeshall MS, et al. Global, regional, and national levels and causes of maternal mortality during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 384:980-1004.

      For every maternal death, 100 women experience severe maternal morbidity.
      • Callaghan W.M.
      • Mackay A.P.
      • Berg C.J.
      Identification of severe maternal morbidity during delivery hospitalizations, United States, 1991–2003.
      • Callaghan W.M.
      • Creanga A.A.
      • Kuklina E.V.
      Severe maternal morbidity among delivery and postpartum hospitalizations in the United States.
      Similar to racial/ethnic disparities in maternal mortality, black women are more likely to suffer from severe maternal morbidity than white women.
      • Callaghan W.M.
      • Mackay A.P.
      • Berg C.J.
      Identification of severe maternal morbidity during delivery hospitalizations, United States, 1991–2003.
      Quality of health care in hospitals is a critical lever for improving outcomes because data suggest more than one third of maternal morbidity and mortality is preventable.
      • Berg C.J.
      • Atrash H.K.
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      Maternal mortality, United States and Canada, 1982–1997.
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      Pregnancy-associated mortality at the end of the twentieth century: Massachusetts, 1990–1999.
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      • Berg C.J.
      Morbidity and mortality in pregnancy: laying the groundwork for safe motherhood.
      Obstetrical complications are sensitive to the quality of care provided at delivery,
      • Guendelman S.
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      Obstetric complications during labor and delivery: assessing ethnic differences in California.
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      and variations in the quality of maternal care across hospitals exists.
      • Howell E.A.
      • Hebert P.
      • Chatterjee S.
      • Kleinman L.C.
      • Chassin M.R.
      Black/white differences in very low birth weight neonatal mortality rates among New York City hospitals.
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      • Horbar J.D.
      • et al.
      Mortality among very low-birthweight infants in hospitals serving minority populations.
      The contribution of hospital quality to racial disparities in obstetrical outcomes has been less studied. The few studies that have examined this topic suggest that racial/ethnic minority women often deliver in lower-quality hospitals.
      • Howell E.A.
      • Egorova N.
      • Balbierz A.
      • Zeitlin J.
      • Hebert P.L.
      Black-white differences in severe maternal morbidity and site of care.
      • Creanga A.A.
      • Bateman B.T.
      • Mhyre J.M.
      • Kuklina E.
      • Shilkrut A.
      • Callaghan W.M.
      Performance of racial and ethnic minority-serving hospitals on delivery-related indicators.
      In our previous work investigating quality measures and severe maternal morbidity in New York City,
      • Howell E.A.
      • Zeitlin J.
      • Hebert P.L.
      • Balbierz A.
      • Egorova N.
      Association between hospital-level obstetric quality indicators and maternal and neonatal morbidity.
      we found wide variation in hospital performance.
      The objective of this study was to examine whether variation in hospital performance on severe maternal morbidity in New York City hospitals contributes to black-white disparities in this outcome. We focus on the black-white severe maternal morbidity disparity because black-white maternal mortality represents the largest disparity among all the conventional perinatal health measures, and the mortality gap between black and white women in NYC has nearly doubled in recent years.
      New York City Department of Health and Mental Hygiene
      Bureau of Maternal and Child Health. Pregnancy-associated mortality, New York City, 2006–2010.
      • Callaghan W.M.
      Overview of maternal mortality in the United States.

      Materials and Methods

      Data source

      We used 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 through 2013. Data linkage was conducted by the New York State Department of Health, and 98.8% of maternal discharge abstracts were linked with infant live birth certificates.
      Institutional review board approvals were 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, ninth revision, Clinical Modification diagnosis and procedure codes and Diagnosis-Related Group delivery codes.
      • Kuklina E.V.
      • Whiteman M.K.
      • Hillis S.D.
      • et al.
      An enhanced method for identifying obstetric deliveries: implications for estimating maternal morbidity.
      From linked records, 4 hospitals with annual delivery volumes less than 5 births and 1360 deliveries with missing hospital identifiers were excluded. The final sample included 353,773 deliveries at 40 hospitals.

      Severe maternal morbidity

      We used a published algorithm to identify severe maternal morbidity, using diagnoses for life-threatening conditions (eg, renal failure, eclampsia) and procedure codes for life-saving procedures (eg, hysterectomy, ventilation, blood transfusion) defined by investigators from the Centers for Disease Control and Prevention.
      • Callaghan W.M.
      • Creanga A.A.
      • Kuklina E.V.
      Severe maternal morbidity among delivery and postpartum hospitalizations in the United States.

      Centers for Disease Control and Prevention. Severe Maternal Morbidity in the United States. Available at: http://www.cdc.gov/reproductivehealth/MaternalInfantHealth/SevereMaternalMorbidity.html. Accessed March 21, 2016.

      As specified by the algorithm, we excluded hospitalizations with a length of stay less than the 90th percentile as calculated separately for vaginal, primary, and repeat cesarean deliveries.
      • Callaghan W.M.
      • Creanga A.A.
      • Kuklina E.V.
      Severe maternal morbidity among delivery and postpartum hospitalizations in the United States.
      All severe maternal morbidity hospitalizations associated with in-hospital mortality and transfer as well as severe complications identified by procedure codes were included, regardless of the length of stay, as recommended.
      • Callaghan W.M.
      • Creanga A.A.
      • Kuklina E.V.
      Severe maternal morbidity among delivery and postpartum hospitalizations in the United States.
      Transfers were defined as discharge disposition after delivery or source of admission for delivery as specified.
      • Callaghan W.M.
      • Creanga A.A.
      • Kuklina E.V.
      Severe maternal morbidity among delivery and postpartum hospitalizations in the United States.

      Covariates

      To risk-adjust hospital-level rates of maternal morbidity, we used variables from the vital statistics records, including mothers’ sociodemographic characteristics (maternal age, self-identified race and ethnicity, parity, education), prenatal care visits, and clinical and obstetric factors (multiple pregnancy, history of previous cesarean delivery, body mass index).
      New York City Vital Statistics collect self-identified race and ethnicity data. We ascertained patient insurance status from the Statewide Planning and Research Cooperative System. We also included diagnoses for patient risk factors that could lead to maternal morbidity but were likely present on admission to the hospital (eg, diabetes, hypertension, obesity, premature rupture of membranes, disorders of placentation). These conditions have been used to risk-adjust for severe maternal morbidity,
      • Gray K.E.
      • Wallace E.R.
      • Nelson K.R.
      • Reed S.D.
      • Schiff M.A.
      Population-based study of risk factors for severe maternal morbidity.
      cesarean deliveries, and other maternal outcomes.
      • Howell E.A.
      • Zeitlin J.
      • Hebert P.L.
      • Balbierz A.
      • Egorova N.
      Association between hospital-level obstetric quality indicators and maternal and neonatal morbidity.
      • Srinivas S.K.
      • Fager C.
      • Lorch S.A.
      Evaluating risk-adjusted cesarean delivery rate as a measure of obstetric quality.
      • Grobman W.A.
      • Feinglass J.
      • Murthy S.
      Are the Agency for Healthcare Research and Quality obstetric trauma indicators valid measures of hospital safety?.
      We obtained teaching status 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 to assess how other hospital characteristics are correlated with severe maternal morbidity.

      Analysis

      We compared the sociodemographic characteristics and clinical conditions of black and white women using χ2 tests. We used a mixed-effects logistic regression with a random hospital-specific intercept to generate risk-standardized severe maternal morbidity rates for each hospital. The models included the covariates described in previous text. Hospital risk-standardized rates were computed from these models using methods recommended by the Centers for Medicare and Medicaid Services Hospital Compare.
      • Howell E.A.
      • Zeitlin J.
      • Hebert P.L.
      • Balbierz A.
      • Egorova N.
      Association between hospital-level obstetric quality indicators and maternal and neonatal morbidity.
      • Ash A.S.
      • Normand S.T.
      • Stukel T.A.
      • Utts J.
      Committee of Presidents of Statistical Societies (COPSS). Statistical issues in assessing hospital performance.
      These rates were the ratio of predicted to expected severe maternal morbidity rates, multiplied by the New York City average severe maternal morbidity rate. For each hospital, the numerator of the ratio is the number of severe maternal morbidity cases predicted on the bases of the hospital’s performance with its case-mix, and the denominator is the number of severe maternal morbidity cases expected on the bases of the New York City performance with that hospital’s case mix. We ranked hospitals from lowest to highest risk-standardized severe maternal morbidity rates. These analyses did not include hospital-level variables.
      We conducted a sensitivity analysis using observed to expected rates for hospital ranking and found that rankings differed very little between the Centers for Medicare and Medicaid Services model and the standard observed to expected ratio. In addition, because blood transfusions are an important component of severe maternal morbidity, we examined the correlation between hospital rankings based on severe maternal morbidity with and without blood transfusion.
      To assess racial 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 black and white mothers. We used the Kolmogorov-Smirnov test to assess whether the distributions of deliveries among hospitals differed for white and black women.
      • Hollander M.
      • Wolfe D.A.
      Nonparametric statistical methods.
      To address the effects on black severe maternal morbidity rates of these differences in delivery location, we conducted a thought experiment and asked what would happen if black mothers went to the same hospitals as white mothers? 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 black mother at each hospital.
      For each black mother, we took the weighted average of these probabilities, in which weights were the percentage of white mothers who went to each hospital. The difference between the predicted probability at the hospital a black mother went to and the weighted average probability if the black mother delivered at the 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 black women is the morbid events avoided if black mothers went to the same hospitals as white mothers or the morbid events because of between-hospital disparities.
      A recent simulation study tested this approach against the more common approach of identifying minority-serving facilities based on the percentage of black patients at a hospital and found that it more accurately measured the magnitude of between-hospital disparities, although both were successful at identifying the existence of disparities.
      • Hebert P.L.
      • Howell E.A.
      • Wong E.S.
      • et al.
      Methods for measuring racial differences in hospitals outcomes attributable to disparities in access to high-quality hospital care.
      To investigate the association between hospital characteristics and severe maternal morbidity rates, we estimated the mixed-effects logistic regression that included maternal sociodemographic and clinical factors as well as the hospital characteristics described in the previous text.
      All statistical analysis was performed using the SAS system software version 9.3 (SAS Institute Inc, Cary, NC).

      Results

      Black mothers accounted for 21% and white mothers for 32% of the 353,773 deliveries in New York City in 2011–2013. The remainder of the births were to Hispanics (29.9%), Asian/Pacific Islanders (16.7%), and others (1.6%). Table 1 shows the sociodemographic and clinical characteristics of black and white deliveries in our study sample. Severe maternal morbidity rates were higher among black (4.2%) as compared with white (1.5%) mothers. As shown in Table 1, maternal characteristics differed significantly between black and white women.
      Table 1Sociodemographic, clinical, and hospital characteristics of deliveries by race and ethnicity in New York City hospitals
      BlackWhiteP value
      n%n%
      Deliveries72,849100110,200100
      Maternal age, y< .0001
       <2052077.1513411.22
       20–2934,81547.7937,81234.31
       30–3417,85924.5238,16134.63
       35–3911,15915.3225,13522.81
       40–4434774.7770796.42
       45 or older3320.466720.61
      Ancestry< .0001
       US born42,18957.9179,93572.54
       Foreign born30,66042.0930,26527.46
      Prepregnancy body mass index, kg/m2< .0001
       Underweight (<18.5)26323.6165495.94
       Normal weight (18.5–24.9)27,78238.1473,01766.26
       Overweight (25.0–29.9)21,23129.1420,23418.36
       Obese (30.0–39.9)17,21223.6390068.17
       Morbid obesity (≥40)34074.6811201.02
       Missing BMI5850.802740.25
      Smoked during pregnancy26733.6725732.33< .0001
      Alcohol use during pregnancy11411.5712201.11< .0001
      Maternal education< .0001
       Less than HS14,60620.0587267.92
       HS19,61426.9220,61218.70
       Greater than HS38,23252.4880,62073.16
       Missing or unknown3970.542420.22
      Insurance< .0001
       Commercial18,29925.1270,10563.62
       Medicaid52,68372.3238,53234.97
       Other6070.838150.74
       Uninsured12601.737480.68
      Prenatal visits<. 0001
       0–5862311.8437373.39
       6–811,50815.8011,05210.03
       ≥951,65870.9194,83386.06
       Unknown10601.465780.52
      Parity< .0001
       Nulliparous41,03356.3358,30852.91
       Multiparous31,69843.5151,74646.96
       Missing1180.161460.13
      Type of pregnancy< .0001
       Singleton71,35997.95107,16597.25
       Multiple14902.0530352.75
      Previous cesarean13,03117.8915,95914.48< .0001
      Comorbidities
       Cardiac disease3100.436160.56< .0001
       Renal disease680.09490.04< .0001
       Musculoskeletal disease2250.313410.31.98
       Digestive disorder170.022690.24< .0001
       Blood disease10,55714.4990138.18< .0001
       Mental disorders30324.1633643.05< .0001
       CNS disease9051.2413101.19.31
       Rheumatic heart disease570.08330.03< .0001
       Disorder placentation16002.2015991.45< .0001
       Chronic hypertension22223.058070.73< .0001
       Pregnancy Hypertension757610.4044114.00< .0001
       Lupus1470.201170.11< .0001
       Collagen vascular disorder240.03720.07.003
       Rheumatoid arthritis610.081490.14.0015
       Diabetes12001.655850.53< .0001
       Gestational diabetes44556.1235343.21< .0001
       Asthma/chronic bronchitis56717.7831742.88< .0001
      Delivery method< .0001
       Cesarean delivery27,67137.9831,40528.50
       Vaginal delivery45,17862.0278,79571.50
      Hospital characteristics
       Hospital ownership< .0001
      Public19,59526.9035743.24
      Private53,25473.10106,62696.76
       Teaching status< .0001
      Not teaching12371.7012001.09
      Teaching71,61298.30109,00098.91
       Nursery level< .0001
      Level 257257.8672196.55
      Level 3–467,12492.14102,98193.45
       Delivery volume< .0001
      Low12,46417.1131432.85
      Medium21,47329.4842033.81
      High17,22823.6522,95420.83
      Very high21,68429.7779,90072.50
      BMI, body mass index; CNS, central nervous system; HS, high school.
      Howell et al. Race, site of care, and severe maternal morbidity. Am J Obstet Gynecol 2016.
      The majority of the 40 hospitals were private, had level 3/4 nurseries, and were teaching hospitals.
      • Howell E.A.
      • Zeitlin J.
      • Hebert P.L.
      • Balbierz A.
      • Egorova N.
      Association between hospital-level obstetric quality indicators and maternal and neonatal morbidity.
      The median percentage of black deliveries was 18.4 (interquartile range, 9.5–35.8%). Hospitals were ranked according to risk-standardized morbidity rates, using a model that included maternal sociodemographic and clinical characteristics associated with severe maternal morbidity (Table 2, model 1).
      Table 2Severe maternal morbidity model for New York City, 2011 to 2013
      Model 1: without hospital characteristics

      Odds ratio (95% CI)
      P valueModel 2: with hospital characteristics

      Odds ratio (95% CI)
      P value
      Maternal age, y
       <201.20 (1.09–1.33)1.19 (1.07–1.31).05
       20–34ReferenceReference
       35–391.20 (1.13–1.27).021.21 (1.14–1.29).03
       40–441.41 (1.29–1.55).061.42 (1.30–1.57).04
       >451.84 (1.45–2.34)< .0011.85 (1.46–2.35)< .001
      Maternal race/ethnicity
       Hispanic1.52 (1.42–1.63).011.40 (1.31–1.51)
       Non-Hispanic black2.02 (1.89–2.17)< .0011.82 (1.69–1.95)< .001
       Non-Hispanic whiteReferenceReference
       Asian1.08 (0.99–1.18)< .0011.09 (0.99–1.18).002
       Other1.31 (0.85–2.04).911.43 (1.31–1.51).90
      Maternal nativity
       Born in the United States0.97 (0.92–1.01).160.97 (0.93–1.02).28
       Foreign bornReferenceReference
      Maternal education
       Less than HS1.12 (1.05–1.19).011.08 (1.008–1.15).07
       HS1.02 (0.96–1.09)< .0011.00 (0.94–1.06)< .001
       Greater than HSReferenceReference
      Insurance
       CommercialReferenceReference
       Uninsured1.27 (1.05–1.53).081.11 (0.92–1.35).43
       Medicaid1.12 (1.05–1.19).801.01 (0.95–1.08).41
       Other1.06 (0.82–1.37).651.07 (0.83–1.38).84
      Prenatal visits
       0–51.42 (1.31–1.52)< .0011.34 (1.24–1.45).004
       6–81.19 (1.12–1.27).301.16 (1.09–1.24).31
       ≥9ReferenceReference
       Unknown1.38 (1.13–1.69).141.35 (1.11–1.65)
      Parity
       NulliparousReferenceReference
       Multiparous0.96 (0.94–0.98)< .0010.96 (0.94–.98)< .001
      Type of pregnancy
       SingletonReferenceReference
       Multiple3.04 (2.76–3.34)< .0013.06 (2.78–3.37)< .001
      Prepregnancy body mass index, kg/m2
       Underweight (<18.5)1.06 (0.95–1.18).750.96 (0.94–0.98).49
       Normal weight (18.5–24.9)ReferenceReference
       Overweight (25.0–29.9)0.99 (0.94–1.05).150.98 (0.93–1.04).15
       Obese (30.0–39.9)0.96 (0.90–1.02).010.94 (0.88–1.004).01
       Morbid obese (≥40)1.13 (1.001–1.28).121.11 (0.98–1.25).16
       Missing1.14 (0.87–1.43).521.08 (0.84–1.38).66
      Smoked during pregnancy0.93 (0.81–1.06).280.92 (0.94–0.98).19
      Alcohol use during pregnancy1.16 (0.99–1.35).071.11 (0.95–1.3).21
      Previous cesarean2.27 (2.16–2.39)< .0012.29 (2.18–2.41)< .001
      Comorbidity
       Cardiac2.90 (2.36–3.94)< .0012.91 (2.36–3.59)< .001
       Musculoskeletal2.72 (0.96–7.72).062.58 (0.91–7.28).07
       Digestive1.19 (0.57–2.48).641.19 (0.57–2.48).64
       Blood disorder3.75 (3.56–3.94)< .0013.73 (3.55–3.91)< .001
       Mental disorder1.40 (1.26–1.55)< .0011.38 (1.25–1.53)< .001
       CNS1.37 (1.15–1.62)< .0011.37 (1.16–1.62)< .001
       Rheumatic heart2.97 (1.81–4.86)< .0012.88 (1.76–4.73)< .001
       Disorder of placentation6.64 (6.13–7.19)< .0016.57 (6.07–7.12)< .001
       Chronic hypertension1.34 (1.17–1.54)< .0011.32 (1.15–1.51)< .001
       Pregnancy hypertension2.95 (2.78–3.13)< .0012.9 (2.73–3.08)< .001
       Lupus0.92 (0.32–2.64).880.97 (0.34–2.76).96
       Collagen/vascular0.45 (0.14–1.52).200.46 (0.34–2.76).21
       Rheumatoid arthritis0.48 (1.16–1.47).200.51 (0.17–1.55).23
       Diabetes1.27 (1.08–1.49).0041.26 (1.08–1.48).004
       Pregnancy diabetes1.21 (1.11–1.32)< .0011.17 (1.08–1.28)< .001
       Asthma/chronic pulmonary1.05 (0.96–1.15).281.05 (0.96–1.15).25
      Hospital characteristics
       Hospital ownership
      Public1.12 (1.06–1.19)< .001
      PrivateReference
       Teaching status
      Not teachingReference
      Teaching0.66 (0.55–0.79)< .001
       Nursery level
      Level 21.27 (1.22–1.33)< .001
      Level 3–4Reference
       Delivery volume
      Low1.69 (1.54–1.85)< .001
      Medium1.53 (1.42–1.65)< .001
      High1.32 (1.23–1.41).16
      Very highReference
      CNS, central nervous system; HS, high school.
      Howell et al. Race, site of care, and severe maternal morbidity. Am J Obstet Gynecol 2016.
      Unadjusted severe morbidity rates ranged from 0.6% to 11.5% and risk standardized rates from 0.8% to 5.7% (Figure 1). The risk standardized morbidity rate for the highest morbidity tertile of hospitals was 3.8% compared with 1.5% for the lowest morbidity tertile (P < .001). Hospital rankings based on severe maternal morbidity with and without blood transfusion were strongly correlated (P < .0001).
      Figure thumbnail gr1
      Figure 1Observed and risk 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.
      SSMMR, standardized severe maternal morbidity rate.
      Howell et al. Race, site of care, and severe maternal morbidity. Am J Obstet Gynecol 2016.
      The cumulative distribution of deliveries among hospitals ranked from lowest to highest morbidity rates differed for black and white mothers (P < .001). The majority of white deliveries (65.3%) occurred in the hospitals in the lowest tertile for severe morbidity compared with 23.3% of all black deliveries. Eighteen percent of white deliveries and 37.3% of black deliveries occurred at hospitals in the highest morbidity tertile (Figure 2). Severe maternal morbidity events and race distribution among hospitals with low (tertile 1) and high (tertile 3) severe maternal morbidity differed (Appendix).
      Figure thumbnail gr2
      Figure 2Cumulative distributions of deliveries according to hospital
      Cumulative distributions of deliveries according to hospital, ranked from lowest to highest morbidity ratio for N-H white mothers and N-H black mothers.
      N-H, non-Hispanic.
      Howell et al. Race, site of care, and severe maternal morbidity. Am J Obstet Gynecol 2016.
      If black mother mothers delivered in the same hospitals as white women, our simulation model estimated that they would experience 940 fewer severe morbid events, leading to a reduction of black severe maternal morbidity rates by 47.7% from 4.2 to 2.9 (1.3 events per 100 deliveries per year).
      Results of our model fitting for severe maternal morbidity rates using maternal and hospital-level variables revealed that teaching status, level 3/4 nursery, private ownership, and very high volume status were associated with lower severe maternal morbidity rates but did not fully account for the excess risk among black women (Table 2, model 2).

      Comment

      Black women are more likely to deliver in New York City hospitals with higher risk-adjusted severe maternal morbidity rates. Severe maternal morbidity rates vary 6-fold across New York City hospitals. Our data demonstrate that racial differences in the distribution of deliveries may contribute to the black/white disparity in severe maternal morbidity rates in New York City hospitals. If black women delivered at the same hospitals as white women, our results suggest that nearly 1000 black women could avoid a severe morbid event during their delivery hospitalization annually in New York City.
      Although much of the focus on reducing racial disparities in obstetrics examines social determinants of health, our results highlight the need to address quality of care as an additional means to reduce racial disparities. Data suggest more than one third of maternal deaths and severe events are preventable.
      • Berg C.J.
      • Atrash H.K.
      • Koonin L.M.
      • Tucker M.
      Pregnancy-related mortality in the United States, 1987–1990.
      • Hoyert D.L.
      • Danel I.
      • Tully P.
      Maternal mortality, United States and Canada, 1982–1997.
      • Nannini A.
      • Weiss J.
      • Goldstein R.
      • Fogerty S.
      Pregnancy-associated mortality at the end of the twentieth century: Massachusetts, 1990–1999.
      • Geller S.E.
      • Cox S.M.
      • Callaghan W.M.
      • Berg C.J.
      Morbidity and mortality in pregnancy: laying the groundwork for safe motherhood.
      Current efforts by the American College of Obstetricians and Gynecologists District II, Merck for Mothers, and the New York State Department of Health have made major efforts to standardize care on labor and delivery units and enhance quality.
      • Kacica M.A.
      Maternal mortality review.

      American College of Obstetricianss and Gynecologists. Safe Motherhood Initiative. 2015. Available at: http://www.acog.org/About-ACOG/ACOG-Districts/District-II/Safe-Motherhood-Initiative-bundles. Accessed June 1, 2016.

      • Arora K.S.
      • Shields L.E.
      • Grobman W.A.
      • D'Alton M.E.
      • Lappen J.R.
      • Mercer B.M.
      Triggers, bundles, protocols, and checklists—what every maternal care provider needs to know.

      Merck for Mothers. Available at: http://www.merckformothers.com/our-work/united-states.html. 2015. Accessed Nov. 5, 2015.

      Data in obstetrics suggest that team building, specific clinical protocols, and improved communication are important targets for quality improvement in the setting of obstetrics and can improve outcomes.
      • Arora K.S.
      • Shields L.E.
      • Grobman W.A.
      • D'Alton M.E.
      • Lappen J.R.
      • Mercer B.M.
      Triggers, bundles, protocols, and checklists—what every maternal care provider needs to know.
      Our findings suggest quality improvement efforts targeting the lowest-performing hospitals may both lower severe maternal morbidity rates for all mothers and narrow the black-white morbidity gap.
      Our findings are consistent with a recent study using national data on delivery hospitalizations, which found that blacks deliver in a concentrated set of hospitals and these hospitals have higher risk-adjusted severe maternal morbidity rates.
      • Howell E.A.
      • Egorova N.
      • Balbierz A.
      • Zeitlin J.
      • Hebert P.L.
      Black-white differences in severe maternal morbidity and site of care.
      Unlike this previous study, the current population-based study used a simulation method to quantify the impact of delivery location on the disparity. Others have also found that black-serving hospitals performed worse than other hospitals on delivery-related indicators using data from seven states.
      • Creanga A.A.
      • Bateman B.T.
      • Mhyre J.M.
      • Kuklina E.
      • Shilkrut A.
      • Callaghan W.M.
      Performance of racial and ethnic minority-serving hospitals on delivery-related indicators.
      In pediatrics, investigators have found that black very low-birthweight babies are more likely to be delivered in higher risk-adjusted very low-birthweight neonatal mortality hospitals, and in other areas of medicine including stroke and heart attack care, studies have documented that black and white patients are treated at different sites of care and black patients are often treated at higher mortality hospitals.
      • Howell E.A.
      • Hebert P.
      • Chatterjee S.
      • Kleinman L.C.
      • Chassin M.R.
      Black/white differences in very low birth weight neonatal mortality rates among New York City hospitals.
      • Morales L.S.
      • Staiger D.
      • Horbar J.D.
      • et al.
      Mortality among very low-birthweight infants in hospitals serving minority populations.
      • Barnato A.E.
      • Lucas F.L.
      • Staiger D.
      • Wennberg D.E.
      • Chandra A.
      Hospital-level racial disparities in acute myocardial infarction treatment and outcomes.
      • Stansbury J.P.
      • Jia H.
      • Williams L.S.
      • Vogel W.B.
      • Duncan P.W.
      Ethnic disparities in stroke: epidemiology, acute care, and postacute outcomes.
      Why hospitals that have a greater proportion of black deliveries experience higher risk-adjusted severe maternal morbidity is not known. Teaching status, level of nursery, volume, and ownership were associated with severe maternal morbidity rates in New York City hospitals but did not fully account for the excess risk among black women.
      The reasons that women deliver at specific hospitals is complex and may be related to a number of factors, including where a patient lives, distance to the hospital, patterns of racial segregation, physician referral, risk perception, patient choice, access, insurance, and the management of possible medical emergencies during pregnancy.
      • Howell E.A.
      • Hebert P.
      • Chatterjee S.
      • Kleinman L.C.
      • Chassin M.R.
      Black/white differences in very low birth weight neonatal mortality rates among New York City hospitals.
      • Hebert P.L.
      • Chassin M.R.
      • Howell E.A.
      The contribution of geography to black/white differences in the use of low neonatal mortality hospitals in New York City.
      Previous studies examining delivery hospital and distance in the setting of very low-birthweight births found that distance did not explain why black women were more likely to deliver at higher risk-adjusted neonatal mortality hospitals.
      • Hebert P.L.
      • Chassin M.R.
      • Howell E.A.
      The contribution of geography to black/white differences in the use of low neonatal mortality hospitals in New York City.
      The extent to which other factors contributed to site of delivery in this study could not be fully evaluated.
      Our analysis has some limitations. We used administrative data (International Classification of Diseases, ninth revision, procedure and diagnosis codes) that do not contain important clinical data on severity of illness. Both Vital Statistics and the Statewide Planning and Research Cooperative System have limitations with reliability of specific variables.
      • Yasmeen S.
      • Romano P.S.
      • Schembri M.E.
      • Keyzer J.M.
      • Gilbert W.M.
      Accuracy of obstetric diagnoses and procedures in hospital discharge data.
      • DiGiuseppe D.L.
      • Aron D.C.
      • Ranbom L.
      • Harper D.L.
      • Rosenthal G.E.
      Reliability of birth certificate data: a multi-hospital comparison to medical records information.
      We used a published algorithm to identify severe maternal morbidity cases and did not conduct a medical chart review for case ascertainment. Nevertheless, 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, maternal education, parity, body mass index).
      We used a simulation model and estimated the extent to which differences in the distribution of deliveries may contribute to disparities. However, similar to others, we were unable to account for unmeasured factors that are associated with both race and severe maternal morbidity. Furthermore, we assumed that unmeasured factors such as social risk are conditionally independent of hospital choice and do not have an impact on the choice of hospital after adjusting for a patient’s measured factors, such as race, education, and insurance. If this assumption is false, our simulation results could exaggerate the role of hospital in black-white severe maternal morbidity disparities. In other words, we would attribute higher rates of severe maternal morbidity to the hospital when some of the excess risk should be attributed to the social risk or other characteristics of the patient population. We focused on black-white differences in distribution of deliveries, given the significant increase in maternal mortality among black women in New York City.
      New York City Department of Health and Mental Hygiene
      Bureau of Maternal and Child Health. Pregnancy-associated mortality, New York City, 2006–2010.
      We found that differences in the hospitals in which black and white women deliver contribute to the disparity in severe maternal morbidity rates between blacks and whites in New York City hospitals. The increasing excess of maternal deaths and high rate of severe morbid events among black women in New York City are concerning. Our data suggests that efforts to improve care at the lowest-performing hospitals may be an important step to reduce these disparities.

      Appendix

      Tabled 1Severe maternal morbidity events and race distribution among hospitals with low (tertile 1) and high (tertile 3) severe maternal morbidity
      VariablesTertile 1, n, %Tertile 3, n, %P value
      Deliveries165,276 (100)87,712 (100)
      Death
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)12 (0.01).03
      Transfers345 (0.21)457 (0.52)< .001
      Hysterectomy222 (0.13)158 (0.18).005
      Ventilation118 (0.07)147 (0.17)< .001
      Renal failure103 (0.06)141 (0.16)< .001
      Cardiac arrest
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01)1.00
      Heart failure procedure333 (0.2)452 (0.52)< .001
      Shock72 (0.04)73 (0.08)< .001
      Sepsis47 (0.03)43 (0.05).009
      Coagulation461 (0.28)450 (0.51)< .001
      Amniotic embolism
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (0.01)<10 (<0.01).07
      Thrombotic embolism26 (0.02)59 (0.07)< .001
      Puerperal CVD54 (0.03)70 (0.08)< .001
      Anesthesia complications35 (0.02)37 (0.04).003
      Pulmonary edema43 (0.03)43 (0.05).003
      Respiratory distress85 (0.05)101 (0.12)< .001
      AMI
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01).42
      Eclampsia40 (0.02)71 (0.08)< .001
      Blood transfusion1686 (1.02)3201 (3.65)< .001
      Sickle cell anemia23 (0.01)31 (0.04)< .001
      Intracranial injury
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01).35
      Injury, thorax/abdomen/pelvis
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01).12
      Aneurysm
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01)1.00
      Heart surgery86 (0.05)95 (0.11)< .001
      Cardio monitoring
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01)1.00
      Tracheostomy
      Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      <10 (<0.01)<10 (<0.01)1.00
      Conversion cardiac rhythm12 (0.01)12 (0.01).13
      Severe maternal morbidity2253 (1.4)3862 (4.4)< .001
      Race/ethnicity
      Differs from percentage given in the manuscript, which measures the percentage of black and white women who deliver in each tertile.
       Asian38640 (23.4)8175 (9.3)< .001
       Black16936 (10.3)27164 (31.0)< .001
       Hispanic35004 (21.2)30883 (35.2)
       White71993 (43.6)19776 (22.6)
       Other race1703 (1.6)1714 (1.9)
      CVD, cardiovascular disease; AMI, acute myocardial infarction.
      Howell et al. Race, site of care, and severe maternal morbidity. Am J Obstet Gynecol 2016.
      a Number of events are masked in the compliance with Statewide Planning and Research Cooperative System regulations
      b Differs from percentage given in the manuscript, which measures the percentage of black and white women who deliver in each tertile.

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      Linked Article

      • Reducing maternal health disparities: the rural context
        American Journal of Obstetrics & GynecologyVol. 216Issue 2
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          We applaud the focus on overcoming racial inequities in maternity care in the recent editorial by Gelber et al,1 bolstered by new empirical findings from Howell et al2 using data from New York City to demonstrate that disparities in maternal morbidity are not just issues of individual race and risk. Rather, a causal factor is structural racism, which occurs when hospital (and other) policies, practices, and norms perpetuate racial group inequities, including in the quality of maternity care.
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