With the increase in obesity and sedentary lifestyles, the prevalence of diabetes mellitus among reproductive-aged women is rising both globally1 and, in the United States, particularly among women of color.2 There are currently 1.85 million reproductive-aged women in the United States with diabetes or glucose intolerance.3 Women of color are at least twice as likely as white women to have type 2 diabetes and 2–3 times more likely to develop diabetes during pregnancy (ie, gestational diabetes).4,5
Partially because of previously small numbers, there are few population-based studies that examine birth outcomes in pregnancies complicated by type 2 diabetes or gestational diabetes.3,6–8 Although recent research has examined racial and ethnic trends in the incidence of type 2 and gestational diabetes,5 few studies have focused on racial differences in birth outcomes in this high-risk group.9 Even fewer studies have attempted to identify or exclude factors that explain racial disparities. And although studies have adjusted for socioeconomic factors, they have been limited in their ability to adjust for diabetes-related intrapartum complications (eg, failure to progress, intrauterine infection).5,9,10 Furthermore, although earlier outcome studies have shown that hospital setting and case volume can affect procedure use,11,12 some studies of diabetic pregnancies have not adjusted for the effect of these hospital characteristics on the use of obstetric procedures.9,10
The goal of this study was to determine whether racial differences existed in the use of child birth procedures and low infant birth weight in pregnancies complicated by type 2 and gestational diabetes mellitus, and if racial differences were found, to elucidate sociodemographic, hospital, and clinical factors that might account for these disparate process and outcome measures. Our hypothesis was that racial differences exist between black and white women and that racial differences in pregnancy-related complications such as preeclampsia might account for some of the disparity in low birth weight infants and procedure use. Our objectives were to estimate 1) the magnitude of racial differences in primary cesarean delivery, episiotomy, and low birth weight in pregnancies complicated by diabetes, 2) the contribution of potential explanatory factors (sociodemographic, hospital, and clinical) to racial differences, and 3) any independent effect of race on the three outcomes of interest after adjusting for explanatory factors. Because of the rising prevalence of type 2 and gestational diabetes, it is important to not only be aware of the magnitude of racial differences, but also to have an understanding of the factors that contribute to racial variations in birth outcomes. If sociodemographic and hospital factors account for racial differences, then a focus on social and organizational interventions is necessary. Alternatively, if racial differences in diabetes-related complications account for racial disparities in procedure use and low birth weight infants, clinicians might devise strategies for preconception and prenatal interventions.
MATERIALS AND METHODS
We conducted a cross-sectional study of 5,507 hospitalizations in which we identified hospital discharges for labor and delivery for pregnancies complicated by type 2 and gestational diabetes mellitus. Pregnancies were included in the study if labor and delivery of the infant occurred between calendar years 1999 and 2004, the pregnancy was a singleton gestation, and if the infant birth weight was 500 g or higher. We excluded pregnancies in which the infant birth weight was less than 500 g to distinguish live births from first- or second-trimester miscarriages. We estimated the association between maternal race and primary cesarean delivery, episiotomy, and low birth weight, adjusting for demographic, hospital, and clinical factors. The study was approved by the Institutional Review Board of the Johns Hopkins School of Medicine.
The data source was the 1999–2004 Maryland Health Care Commission Database,13 which has been previously used to examine trends in care for perinatal complications14 and complications of chronic disease.15,16 Hospitals within the state are required to submit patient discharge data to the Commission on a routine basis. Routine chart audits are conducted by the state to ensure accuracy, and agreement of data submitted with data from medical records and is reported to be as high as 97%.17 Requests for data are submitted to the Commission's data review board. Upon approval, data elements devoid of patient identifiers are distributed to investigators.
The Maryland Health Care Commission Database contains information on all nonfederal hospital discharges within the state. Information on Maryland residents discharged from hospitals in neighboring states is not included in the database. The data set contains information on patient demographics, primary insurers, primary discharge diagnosis and up to six secondary diagnoses, and principal procedure and up to six secondary procedures. Discharge diagnoses and clinical procedures are listed as International Classification of Diseases, 9th Revision (ICD-9) procedure codes.
The identification of maternal hospital discharges for pregnancies complicated by diabetes that resulted in the labor and delivery of an infant was achieved using ICD-9 codes. We identified hospital discharges for labor and delivery with gestational diabetes (ICD-9 code 648.8X) or pregestational diabetes (ICD-9 648.0X). Because the ICD-9 code 648.0X includes both type 1 and type 2 diabetes, we cross-referenced this group of discharges with the diagnosis code for type 2 diabetes (ICD-9 code 250.0X). Because the state does not routinely link mother and infant files with an unique identifier due to concerns regarding confidentiality, we developed a set of matching algorithms to link mother and infant files based on 1) hospital of delivery, 2) date of discharge for mother and infant, 3) maternal date of delivery and infant birth date, 4) maternal and infant ZIP code, and 5) maternal and infant race.
We chose three outcomes for the analysis: primary cesarean delivery, episiotomy with and without concurrent lacerations, and low infant birth weight. We chose cesarean delivery and episiotomy because these procedures are established measures of potential maternal morbidity in childbirth.18 Recent reports support potentially higher complication rates among women with diabetes or obesity who are undergo cesarean delivery.19 With the rising incidence of diabetes among reproductive-aged women and the disproportionate number of black women with diabetes, an excess of these procedures among black women might indicate greater childbirth morbidity in this population. We chose low infant birth weight as an outcome because it is associated with higher neonatal morbidity and resource use and is included as a targeted area in the Healthy People 2010 report.20 Further, because both type 2 and gestational diabetes can be complicated by hypertensive disease, which could lead to vascular disease and poor infant growth or indicated early delivery due to maternal or fetal complications, we thought it important to focus on low birth weight as a potential complication of this comorbidity. Primary cesarean delivery, episiotomy, and low birth weight (less than 2,500 g compared with 2,500 g or greater) were modeled as dichotomous variables.
The primary independent variable, maternal race, was based on maternal self-report at the time of admission to labor and delivery and included non-Hispanic whites, non-Hispanic blacks, Asian/Asian Pacific Islanders, American Indians, and “other.” Sociodemographic variables included maternal age, parity (nulliparity, multiparity), principal insurer (which we classified as commercial, health maintenance organization [HMO], Medicaid, self-pay), and marital status (married, single).
Clinical variables included pre-existing medical factors such as chronic hypertensive disease (pre-existing chronic hypertension) and maternal obesity (excessive weight gain, obesity, morbid obesity), and clinical factors developed during pregnancy (preeclampsia [hypertensive disease developing in pregnancy], chronic hypertension with superimposed preeclampsia, low infant birth weight), and insufficient maternal weight gain. We included chronic hypertensive disease and preeclampsia as separate clinical variables because the development of each type of hypertensive disease can occur at different points in the course of pregnancy.4 Intrapartum clinical factors included infection (chorioamnionitis), failed attempt at labor (failure to progress, failed induction, failure of descent, pelvic dystocia), and fetal heart rate abnormality. We included category of diabetes as type 2 or gestational diabetes mellitus. We also included history of previous cesarean delivery and operative vaginal delivery (vacuum or forceps delivery).
Hospital characteristics included year of discharge (1999–2000, 2001–2002, and 2003–2004), teaching status, and volume of cases. We classified hospitals as teaching (n=9) or nonteaching (n=28). Hospital volume categories were based on the distribution of deliveries of diabetic pregnancies over the 6-year study period. High-volume institutions (n=6) had more than 400 deliveries (50 per year on average). Medium-volume institutions (n=10) had between 200 and 400 diabetic deliveries, and low-volume institutions (n=21) had fewer than 200 deliveries (fewer than 2.5 per year on average).
Demographic, clinical, and hospital factors were compared between racial groups using the χ2 statistic for categorical variables and the t test for continuous variables. We estimated the rate of cesarean delivery, episiotomy, and low infant birth weight for black and white women using χ2 statistics. Women who underwent prior cesarean delivery were excluded from the calculated cesarean delivery rate. Women with current cesarean delivery were excluded from the calculated rate of episiotomy. In univariable analyses, we estimated the unadjusted association between covariates and each outcome, calculating unadjusted odds ratios and 95% confidence intervals. We evaluated potential collinearity among the sociodemographic variables using a correlation matrix (correlation coefficient 0.4 or higher) and the variance inflation factor.21
To estimate the independent effect of race on primary cesarean delivery, episiotomy, and low birth weight in diabetic pregnancies, we developed separate multiple logistic regression models20 for each outcome to adjust for potential confounders. We adjusted for the categories of sociodemographic, clinical, and hospital factors in which there was an association with both race and the outcome of interest from the univariable analysis or if the variable was known to be clinically associated with the outcome. Explanatory variables were added in a stepwise fashion: sociodemographics first (age, single status, Medicaid coverage, HMO versus commercial), then hospital factors (teaching status versus nonteaching, high volume and low volume versus medium volume), then pre-existing clinical factors (chronic hypertension, maternal obesity), then clinical factors developed during pregnancy (preeclampsia or chronic hypertension with superimposed preeclampsia; high infant birth weight), then intrapartum clinical factors (infection, fetal heart rate abnormality), then category of diabetes (type 2 versus gestational diabetes). Because chronic hypertension with superimposed preeclampsia could be included in the categories of hypertension or preeclampsia or both, we first adjusted for this variable under the category of hypertension and later in the category of preeclampsia. Because there was no significant change in the models, we included it in the category of preeclampsia in the final analysis. Because we did not have biological measures to adjust for the severity of insulin resistance, we adjusted for the category of diabetes, recognizing the higher severity of insulin resistance and glucose intolerance with type 2 diabetes relative to gestational diabetes. High infant birth weight was included only in the models for cesarean delivery and episiotomy. The model for cesarean delivery was also adjusted for failed attempt at labor. The model for episiotomy was also adjusted for operative vaginal delivery (forceps or vacuum). Because poor maternal weight gain is a risk factor for low infant birth weight, we adjusted for insufficient maternal weight gain in the multivariate model for low infant birth weight. To evaluate for the presence of interactions, we included an interaction term with race and each of the sociodemographic (age, marital status, payer source) and hospital factors (teaching status, hospital volume) in the fully adjusted logistic regression models. P<.05 was considered significant.
We also conducted subgroup analyses, in which we developed logistic regression models for each outcome stratified by category of diabetes (type 2 and gestational). We had 80% and 90% power to detect a 10% difference in rates of cesarean, episiotomy, and low infant birth weight by race in pregnancies with type 2 and gestational diabetes, respectively. P<.05 was considered significant. All analyses were conducted using STATA 8 (StataCorp, College Station, TX).
There were 6,310 hospitalizations for delivery for pregnancies complicated by type 2 and gestational diabetes out of 159,537 hospitalizations for delivery in Maryland in our data set during the 6-year study period, which corresponds to a prevalence of 3.9%. There were 5,364 (85%) hospitalizations among women with gestational diabetes and 946 (15%) hospitalizations among women with type 2 diabetes. We initially identified 6,310 hospitalizations with type 2 or gestational diabetes that were eligible for matching with infant files. We were able to link 5,507 (87%) of the eligible maternal files with infant files. We excluded those mothers who did not match to an infant (n=683). These mothers primarily delivered outside of the hospital and were admitted for postpartum care only, delivered a stillborn, or were admitted with the codiagnosis of spontaneous miscarriage. Also, we excluded mothers who matched to more than one infant (n=120) due to multiple gestations. A higher percentage of mothers in the excluded group (n=803) delivered between 1999 and 2000 and had a history of prior cesarean delivery compared with the 5,507 mothers who matched to infants (Table 1). The composition of maternal race was 3,150 white (57%), 1,555 black (28%), 290 Asian (5%), and 495 (9%) “other” race. Due to small numbers in other minority groups, we limited the analysis to black and white women.
Black women were younger and more likely to be single and to be covered by Medicaid insurance than their white counterparts (Table 1). Blacks and whites were hospitalized with similar frequencies at teaching hospitals and at high-volume hospitals, although the differences were statistically significant. Over one fifth of pregnancies among blacks were complicated by type 2 diabetes compared with 13% among whites. Pregnancies among black women were also more likely to be complicated by preeclampsia and fetal heart rate abnormalities compared with pregnancies among white women. The percentage of low birth weight infants was significantly higher among blacks than whites.
Pregnancies among black women had a higher rate of cesarean delivery and low infant birth weight, but a lower rate of episiotomy, than those among white women. In unadjusted analysis, black race was associated with higher odds of cesarean delivery and low infant birth weight and lesser odds of episiotomy (Table 2).
In the unadjusted analysis, black women had 40% and 94% higher odds of cesarean delivery and low birth weight, respectively, than white women. Conversely, black women had 62% lesser odds of episiotomy than white women. After adjustment for sociodemographic and hospital factors, black women had a 36% higher odds of cesarean delivery than white women (odds ratio [OR] 1.36, 95% confidence interval [CI] 1.16–1.58) (Table 3). After addition of intrapartum infection and low infant birth weight to the model, the odds of cesarean delivery increased slightly for black women. In the fully adjusted model, black race was associated with a 1.38 higher odds of cesarean delivery.
After adjustment for sociodemographic factors, black women had 53% lesser odds of episiotomy (OR 0.47, 95% CI 0.38–0.58) than white women. Further adjustments slightly attenuated the relationship, but the odds ratio remained statistically significant.
Black women had a higher odds of low infant birth weight after adjustment for sociodemographic factors (OR 2.03, 95% CI 1.60–2.58) than white women. After further adjustment for hospital factors, the association of black race with infant low birth weight was modestly attenuated. In the full model with adjustment for the category of diabetes, the odds of low infant birth weight among black women was attenuated but remained statistically significant (OR 1.81, 95% CI 1.41–2.34). The magnitude of association between black race and each outcome did not vary at different levels of maternal age, marital status, payer source, or hospital characteristics(data not shown).
There were no differences in the direction of association of black race with procedure use or low infant birth weight by category of diabetes. Compared with white women, the odds of cesarean delivery was 42% and 36% higher among black women with gestational (OR 1.42, 95% CI 1.23–1.66) and type 2 diabetes (OR 1.36, 95% CI 0.93–1.96), respectively (Table 4). Black women with gestational and type 2 diabetes had a 96% and 55% higher odds, respectively, of low birth weight infants compared with their white counterparts. The odds of episiotomy among black women was similar across diabetes categories.
Although many studies document racial disparities in patient outcomes, elucidating or excluding pathways to explain these disparities can assist in the development of focused interventions to eliminate them. We conducted a population-based, cross-sectional study to better understand the association of maternal race with childbirth procedures and low birth weight infants in pregnancies with type 2 and gestational diabetes. Even after adjustment for several demographic, hospital, and clinical factors, black women with diabetes have a greater likelihood of cesarean delivery and low birth weight infants and a lower likelihood of episiotomy.
We hypothesized that racial differences in the development of diabetes-related complications (e.g. pre-eclampsia, fetal heart rate abnormalities) would partially explain variations in cesarean delivery and low birthweight infants. Through compromised placental vasculature, pre-eclampsia can contribute to diminished fetal growth and term, low birthweight infants who, in turn, exhibit fetal heart rate abnormalities during labor and are delivered by cesarean section. Also, pre-eclampsia can compromise both maternal and fetal well-being, necessitating cesarean delivery of a preterm, low birthweight infant. We found 50% higher rates of pre-eclampsia and fetal heart rate abnormalities among blacks compared to whites, which is consistent with results from other studies of general and high-risk obstetrical patients. We also found support for our hypothesis, since adjustment for the presence of fetal heart rate abnormalities modestly attenuated the association of black race with cesarean delivery.
In our study, 13% of black women underwent episiotomy, compared with 27% of white women. Although there is no optimal episiotomy rate based on current evidence, rates of 10–15% in general obstetric populations are considered acceptable.22 We report a 55% lesser odds of episiotomy among black women than white women, which is also consistent with prior findings. Data from the National Hospital Discharge Survey show a 54% lower odds of episiotomy in mostly healthy black women compared with white women.22 Variations in episiotomy rates are generally attributed to differences in physician practice patterns or provider beliefs about potential benefits compared with the risks of the procedure.23,24 Among women with diabetes, physicians might elect not to perform an episiotomy because of concerns about possible birth trauma (ie, shoulder dystocia, Erb's palsy) in women with poor glucose control and potentially large for gestational age or macrosomic infants. Because black women in this sample had infants with lower birth weight, we adjusted for birth weight in our analysis, but the lower odds of episiotomy among black women remained statistically significant.
While variations in episiotomy rates have not been fully explained by sociodemographic factors, prior studies show higher rates among white and married women and women with commercial insurance.18 Adjustment for these factors in our analysis slightly attenuated the association of black race with episiotomy, which would suggest that maternal demographics might partially account for observed racial differences. Finally, in stratified analysis, the relation of black race with episiotomy was similar across age categories, payer groups, and hospital teaching status. These results further support the idea that additional factors account for the association of black race with performance of episiotomy.
Prior studies show that racial variations in procedures can be attributed to differences in patient preferences,25 patient-physician communication,26 disparities in the quality of prenatal health care,27 or physician practice patterns.28 In our sample, black women may have had specific preferences for obstetric procedures based on cultural perceptions or prior delivery experiences. Alternatively, poor patient-physician communication due to racial or ethnic differences between patients and physicians26 might have resulted in inadequate knowledge about treatment options or lack of involvement in decision making, both of which could lead to lower adherence to physician recommendations among black women. Differences in access to prenatal care might have also contributed to poor glucose control, leading to obstetric complications, low birth weight, and a greater number of procedures. Finally, earlier studies have shown that physician recommendations for procedures can be based on a complex interplay of clinical perceptions and patient race. These associations have been repeatedly demonstrated, for example, in studies on the use of cardiac procedures.29 Differences in practice patterns may also suggest the need for interventions to improve patient-physician communication as a strategy for improving patient involvement in decisions and adherence. Alternatively, the practice setting, including availability of in-house anesthesiologists or obstetricians and highly skilled nursing, may affect the decision for cesarean delivery or episiotomy. Future study, with adjustment for both the type and number of personnel, might further reduce current racial differences.
Our study has several strengths. We used a population-based sample to examine racial differences in childbirth procedures and low birth weight infants. Because we drew the study sample from a large population of women who delivered infants during 5 years in one state, we were able to examine racial differences among women with type 2 and gestational diabetes mellitus. Because the database contains up to seven secondary diagnosis codes, we were able to adjust for multiple co-conditions specific to diabetes in pregnancy. Few studies of diabetes in pregnancy have been able to do this. Also, the database provides information on hospital characteristics, which we were able to adjust for in the multivariable models. In interpreting our findings, however, it is important to consider several potential limitations. First, our results are based on an analysis of administrative data. Administrative databases are limited by less detailed clinical information. For example, we were unable to measure the severity of preeclampsia in the current study. Prior studies suggest that ethnicity can be associated with earlier development and greater severity of preeclampsia.9,30 Early onset of preeclampsia can prompt the delivery of low birth weight preterm or term infants. We based our risk adjustment primarily on sociodemographic data and additional discharge diagnoses.31 Although this strategy has been used successfully in previous studies of administrative data, we acknowledge the lack of adjustment for actual maternal weight, measures of glucose control, and prenatal care use, three factors that could affect infant birth weight and the decision for cesarean delivery or episiotomy. The prevalence of obesity in our sample is lower than national estimates. It is probable that obesity was underreported in our sample for both black and white women. Incomplete adjustment for maternal obesity may account for some of the residual racial disparity in cesarean delivery after adjustment for other sociodemographic and clinical factors. Also, we could not ascertain the appropriateness of procedure use or measure the quality of individual physician's decisions. Also, several important social factors, such as maternal education and income, were not included in the database. Finally, as with any discharge database, there could be errors in coding. However, the Maryland Health Care Commission conducts routine audits of the data from each Maryland hospital and reports appropriate levels of accuracy.17
Although further study is warranted, our findings have important implications for reproductive-aged women and for the study of racial differences in childbirth procedures. First, obstetricians and primary care physicians might target reproductive-aged women in their practices for educational interventions to reduce their risks of developing gestational or type 2 diabetes. Second, our findings suggest the need to further explore whether racial differences might be explained by differential access to health care. Finally, our findings suggest the need to examine patient-physician communication or provider bias in a racially diverse, patient-physician environment. If this is an important factor, as in other clinical areas, policies that integrate cultural competency into physician training might alleviate barriers in communication that contribute to current disparities in obstetric procedure use.
1. Feig DS, Palda VA. Type 2 diabetes in pregnancy: a growing concern. Lancet 2002;359:1690–2.
2. Ferrara A, Kahn H, Quesenberry CP. An increase in the incidence of gestational diabetes mellitus: Northern California, 1991–2000 [published erratum appears in Obstet Gynecol 2004;103:799]. Obstet Gynecol 2004;103:526–33.
3. Beckles GLA, Thompson-Reid PE, editors. Diabetes and women's health across the life stages: a public health perspective. Atlanta (GA): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Division of Diabetes Translation; 2001.
4. Gabbe SG, Graves C. Management of diabetes mellitus complicating pregnancy. Obstet Gynecol 2003;102:857–68.
5. Thorpe LE, Berger D, Ellis JA, Bettegowda VR, Brown G, Matte T, et al. Trends and racial/ethnic disparities in gestational diabetes among pregnant women in New York City, 1990–2001. Am J Public Health 2005;95:1536–9.
6. Jacobson JD, Cousins L. A population-based study of maternal and perinatal outcomes in patients with gestational diabetes. Am J Obstet Gynecol 1989;161:981–6.
7. Vangen S, Stoltenberg C, Holan S, Moe N, Magnus P, Haris JR, et al. Outcome of pregnancy among immigrant women with diabetes. Diabetes Care 2003;26:327–32.
8. Schaefer-Graf U, Xiang A, Songster G, Montoro M, Kjos SL. Patterns of congenital anomalies and relationship to initial maternal fasting glucose levels in pregnancies complicated by type 2 and gestational diabetes. Am J Obstet Gynecol 2000;182:313–20.
9. Rosenberg TJ, Garbers S, Lipkind H, Chiasson MA. Maternal obesity and diabetes as risk factors for adverse pregnancy outcomes: differences among 4 racial/ethnic groups. Am J Public Health 2005;95:1545–51.
10. Feig DS, Razzaq A, Sykora K, Hux JE, Anderson GM. Trends in Deliveries, Prenatal Care, and Obstetrical Complications in Women With Pregestational Diabetes: a population-based study in Ontario, Canada, 1996–2001. Diabetes Care 2006;29:232–5.
11. Oleske DM, Branca ML, Schmidt JB, Ferguson R, Linn ES. A comparison of capitated and fee-for-service Medicaid reimbursement methods on pregnancy outcomes. Health Serv Res 1998;33:55–73.
12. Oleske DM, Glandon GL, Giacomelli GJ, Hohmann SF. The cesarean birth rate: influence of hospital teaching status. Health Serv Res 1991;26:325–37.
13. The Maryland Health Services Cost Review Commission. Case mix data. Available at: http://www.hscrc.state.md.us/case_mix/CaseMixReport.htm
. Retrieved June 9, 2006.
14. Garcia FA, Miller H, Huggins GR, Gordon TA. Effect of academic affiliation and obstetric volume on clinical outcomes and cost of childbirth. Obstet Gynecol 2001;97:567–76.
15. Steiner CA, Bass E, Talamini MA, Pitt HA, Steinberg EP. Surgical rates and operative mortality for open and laparoscopic cholecystectomy in Maryland. N Engl J Med 1994;330:403–8.
16. Sosa JA, Bowman H, Tielsch JM, Powe NR, Gordon TA, Udelsman R. The importance of surgeon experience for clinical and economic outcomes from thyroidectomy. Ann Surg 1998;228:320–30.
17. The Johns Hopkins Hospital report of clinical data quality review. Baltimore (MD): Deloitte, Haskins, & Sells; 1998.
18. Hartmann K, Viswanathan M, Palmieri R, Gartlehner G, Thorp J Jr, Lohr KN. Outcomes of routine episiotomy: a systematic review. JAMA 2005;293:2141–8.
19. Robinson HE, O'Connell CM, Joseph KS, McLeod NL. Maternal outcomes in pregnancies complicated by obesity. Obstet Gynecol 2005;106:1357–64.
20. U.S. Department of Health and Human Services. Healthy People 2010: understanding and improving health. 2nd ed. Washington, DC: Department of Health and Human Services; 2000.
21. Hosmer DW, Lemeshow S. Applied logistic regression. New York (NY): John Wiley; 1989.
22. Weber AM, Meyn L. Episiotomy use in the United States, 1979–1997. Obstet Gynecol 2002;100:1177–82.
23. Bansal RK, Tan WM, Ecker JL, Bishop JT, Kilpatrick SJ. Is there a benefit to episiotomy at spontaneous vaginal delivery? A natural experiment. Am J Obstet Gynecol 1996;175:897–901.
24. Klein MC, Kaczorowski J, Robbins JM, Gauthier RJ, Jorgensen SH, Joshi AK. Physicians' beliefs and behaviour during a randomized controlled trial of episiotomy: consequences for women in their care. CMAJ 1995;153:769–79.
25. Horner RD, Oddone E, Matchar DB. Theories explaining racial differences in the utilization of diagnostic and therapeutic procedures for cerebrovascular disease. Milbank Q 1995;73:443–62.
26. Cooper LA, Roter DL, Johnson RL, Ford DE, Steinwachs DM, Powe NR. Patient-centered communication, ratings of care, and concordance of patient and physician race. Ann Intern Med 2003;139:907–15.
27. Karter AJ, Ferrara A, Liu JY, Moffet HH, Ackerson LM, Selby JV. Ethnic disparities in diabetic complications in an insured population. JAMA 2002;287:2519–27.
28. van Ryn M, Burgess D, Malat J, Griffin J. Physicians' perceptions of patients' social and behavioral characteristics and race disparities in treatment recommendations for men with coronary artery disease. Am J Public Health 2006;96:351–7.
29. Kressin NR, Petersen LA. Racial differences in the use of invasive cardiovascular procedures: review of the literature and prescription for future research. Ann Intern Med 2001;135:352–66.
30. Vambergue A, Nuttens M, Goeusse P, Biausque S, Lepeut M, Fontaine P. Pregnancy-induced hypertension in women with gestational carbohydrate intolerance: the diagest study. Eur J Obstet Reprod Biol 2002;102:31–5.
31. Polanczyk CA, Rohde LE, Philbin EA, Di Salvo TG. A new casemix adjustment index for hospital mortality among patients with congestive heart failure. Med Care 1998;36:1489–99.