The Journal of Maternal-Fetal Medicine 7:23–27 (1998)
Racial Differences in Outcome of Pregnancies Complicated by Hypertension Lucky Jain, MD,1* Cynthia Ferre, PhD,2 and D. Vidyasagar, MD1 1Department 2Department
of Pediatrics, University of Illinois, Chicago, Illinois of Epidemiology, University of Illinois, Chicago, Illinois
Abstract
Racial differences in the outcome of pregnancies complicated by hypertension (HTN) were examined using data obtained from a large perinatal data base with 109,428 consecutive deliveries from 1982 to 1987. Black women had a higher prevalence of hypertension than white women (prevalence ratio 2.3, 95% CI 2.2, 2.5). However, when compared to normotensive women of similar race, white hypertensive women showed a higher risk for adverse pregnancy outcome than black hypertensives as indicated by the higher odds ratio for prematurity (OR: 1.7 for white [W], 1.2 for black [B]), low birth weight (OR: 2.4 W; 1.5 B), intrauterine growth retardation (OR: 4.4 W; 1.6 B) and perinatal death (OR 2.3 W; 1.2 B). Hypertension was associated with a 156 g reduction in birthweight of newborns in whites as compared to a 63 g reduction in blacks. Further studies are needed to understand the racial differences in the impact of HTN on pregnancy outcome. J. Matern.–Fetal Med. 7:23–27, 1998. r 1998 Wiley-Liss, Inc.
Key Words: hypertension; race; pregnancy outcome
INTRODUCTION Hypertension (HTN) is one of the most common medical complications of pregnancy and is a major cause of perinatal morbidity and mortality [1–4]. Racial differences in the prevalence of HTN have been reported with blacks of African origin having a higher prevalence of HTN than whites [5–7]. The effect of race on the outcome of pregnancies complicated by HTN is not well known, although black women are generally believed to be at a greater risk for hypertension-related complications [8]. De Baun et al. [9] recently suggested that white mothers with pregnancyinduced HTN are at a greater risk for delivering very-lowbirth weight (,1,500 g) infants than black mothers. In the present study, using our perinatal data base, we investigated the racial differences in the outcome of pregnancies complicated by HTN. METHODS Data for this study were obtained from the University of Illinois Regional Perinatal Network, a perinatal data collection system described previously [10]. Briefly, it consists of prospective abstraction of information from medical records of 11 level II and 2 level III hospitals in the network. The designation of care level is based on the expertise of personnel and the facilities for perinatal care available at these centers [11]. Seventy-three elements and 300 varir 1998 Wiley-Liss, Inc.
ables are evaluated and data entered into an IBM mainframe computer. The abstractors are trained in data collection and are university employees so that quality can be monitored. Direct access to medical records reduces the problem of unreliable data that can occur when outside data sources are used. The entire system is subject to periodic reviews for quality control. The data base was closed to new data acquisition in 1987. From 1982 through 1987, data from 109,428 motherinfant pairs were abstracted. Of these, 56,451 (51.6%) were white, 24,986 (22.8%) were black, and the remaining 27,991 (25.6%) were of Hispanic, Asian, or other unclassified ethnic origin. Analyses in this study were restricted only to the black and the white women, for a total of 81,437. Hypertension during pregnancy was defined using the following criteria proposed by the American College of Obstetricians and Gynecologists [12]: (1) systolic blood pressure $140 mm Hg, (2) diastolic blood pressure $90 mm Hg, and (3) increase of $30 mm Hg in systolic pressure. Any of these criteria were required to be present on at least two occasions separated by at least 6 hours. Preeclampsia or *Correspondence to: Lucky Jain, M.D., who is now at the Department of Pediatrics, Emory University School of Medicine, 2040 Ridgewood Drive, Atlanta, GA 30322. E-mail:
[email protected] Received 12 May 1997; revised 11 September 1997; accepted 11 September 1997
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JAIN ET AL. TABLE 1. Demographic Characteristics of Study Population Blacks
Whites
Characteristic
Nonhypertensive
Hypertensive
Nonhypertensive
Hypertensive
n Age: years, x (SD) Systolic BP: mm Hg, x (SD) Diastsolic BP: mm Hg, x (SD) Pregnancy-induced hypertension (n) Chronic hypertension (n) Birthweight: g, x (SD) Gestational age: wk, x (SD)
22,481 23.9 (5.8) 125.9 (17.2) 77.9 (23.6) — — 3,077 (656) 38.5 (3.8)
2,505 (10%) 24.8 (6.8) 145.9 (20.6) 90.9 (14.5) 1,676 829 3,014 (724) 38.5 (3.5)
53,926 27.8 (5.2) 126.1 (15.2) 77.8 (23.7) — — 3,360 (636) 39.1 (4.0)
2,525 (4.5%) 27.8 (5.7) 145.7 (18.9) 90.2 (13.4) 1,694 831 3,204 (796) 38.8 (3.2)
toxemia was recorded if hypertension was accompanied by edema and proteinuria. Chronic hypertension was defined as blood pressure $140 mm Hg systolic, or 90 mm Hg diastolic detected earlier than the 20th week of pregnancy, or dating to the prepregnancy period. If hypertension was first noticed any time after the 20th week (excluding the intrapartum period), but was not accompanied by signs of toxemia, it was recorded as pregnancy-induced hypertension. Statistical Analysis The effect of race and hypertension on pregnancy outcome was examined. For categorical variables, the Chisquare test and Fischer’s exact test were employed. The Student’s t-test and ANOVA were used to compare means. Significant adverse outcomes of pregnancy complicated by hypertension in both the black and the white races were analyzed with the Mantel-Haenszel Chi-square test. Stepwise logistic multivariate analysis was performed to identify significant independent relationships. A P value of #0.05 was considered significant. Data retrieval and analysis were done with Statistical Analysis Systems Software [13]. RESULTS Among the 24,986 black and the 56,451 white women (totaling 81,437), 5,030 hypertensive pregnancies were identified for a prevalence rate of 6.2%. The demographic characteristics of the study population are shown in Table 1. Black women had a higher prevalence of hypertension than white (prevalence ratio 2.3, 95% CI 2.2, 2.5). Table 2 shows the age-specific prevalence of HTN among black mothers and white mothers. Black mothers had a higher prevalence of HTN at all ages; however, older black women carried a disproportionately higher risk for hypertension. Black women had a higher prevalence of both pregnancy-induced hypertension (B 6.7%, W 3.0%) and chronic hypertension (B 3.3%, W 1.5%). Blacks had less prenatal care than whites (#3 prenatal visits; B 18.4%, W. 7.2%).
TABLE 2. Age-specific Prevalence of Hypertension According to Race, Controlling for Age Age (yr)
Blacks (%)
Whites (%)
Prevalence ratio
95% Confidence interval
,20 20–29 30–39 $40
10.8 8.3 13.8 25.8
7.9 5.7 6.2 9.4
1.4 1.5 2.2 2.8
1.2–1.6 1.4–1.6 2.0–2.5 1.9–4.0
Prevalence rates of selected adverse outcomes based on race and hypertension status are shown in Table 3. When compared to nonhypertensive white women, nonhypertensive black women had worse outcomes in all of the categories studied. However, white hypertensives had higher risk for neonatal death, perinatal death, and intrauterine growth retardation, when compared to black hypertensives. Figure 1 shows odds ratio for the adverse outcomes reported in Table 3 for pregnancies with hypertension. Hypertension increased the odds ratio for adverse outcome in both races, but the effect was proportionately greater in white pregnancies for fetal death, neonatal death, intrapartum-maternal complications, prematurity, and intrauterine growth retardation. Using a fully qualified logistic regression model, these racial differences persisted for the occurrence of neonatal death (P , .002), prematurity (P , .0001), and IUGR (P , .0001). When compared to normotensive women of similar race, white hypertensive women had a greater reduction in infant birthweight (156 g) than black hypertensives (63 g) (P , .0001). DISCUSSION Our findings demonstrate that: (1) hypertension during pregnancy is associated with a significant increase in the risk for adverse outcome, (2) black women have a higher prevalence of hypertension during pregnancy, (3) when measured as a ratio, the hypertension associated risk for
HYPERTENSION DURING PREGNANCY
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TABLE 3. Changes in Odds Ratio (OR)* for Various Adverse Outcomes Among Blacks and Whites With Control for Hypertension
Adverse outcome Fetal death Neonatal death Perinatal death Low birthweight Prematurity Intrauterine growth retardation
OR for adverse OR for adverse OR for adverse outcome in blacks outcome in whites outcome in black (HTN vs. no HTN) (HTN vs. no HTN) HTN vs. white HTN 2.1 (1.5–2.8) 0.6 (0.9–1.9) 1.2 (0.9–1.6) 1.5 (1.4–1.6) 1.2 (1.1–1.4) 1.6 (1.3–1.9)
2.4 (1.7–3.2) 2.2 (1.6–3.0) 2.3 (1.8–2.9) 2.4 (2.2–2.6) 1.7 (1.6–1.8) 4.4 (3.7–5.2)
1.26 (0.77–2.04) 0.48 (0.25–0.93) 0.88 (0.60–1.28) 1.27 (0.82–1.96) 1.15 (0.75–1.79) 0.96 (0.74–1.25)
*95% confidence limits for OR in parenthesis.
Fig. 1. Percentage distribution of various adverse pregnancy outcomes by maternal race and hypertension. A, blacks, B, whites.
adverse pregnancy outcome is more pronounced in white women than blacks. The prevalence of HTN during pregnancy reported in this study (6.2%) is comparable to that found by several other investigators [1]. Our data are consistent with results of previous investigations showing a considerable increase
in morbidity and mortality in pregnancies complicated by HTN. The perinatal mortality in hypertensive pregnancies in this study (2.4%) is lower than that reported by Ployin et al. (5.7%) [14] and Svensson et al. (3.8%) [15]. Rey and Couturier [16] reported a perinatal mortality of 4.5% in women with chronic hypertension compared to 1.2% in the
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JAIN ET AL.
Figure 1. (Continued.)
general population. The risk for intrauterine growth retardation with hypertension is also lower in this study (5.0%) as compared to some previous investigations reporting up to 19% rate of IUGR [1,15]. All cases of hypertension were included in our study as long as they satisfied the ACOG criteria in contrast to other prospective studies where more stringent criteria for defining HTN were employed. The criteria for diagnosis of HTN during pregnancy have undergone changes from the time that these data were collected. This is not unusual considering the length of time required to collect a cohort of this size. These changes should be kept in mind when comparing data from this and other previously published reports to more recently collected data using revised guidelines. Our finding of increased prevalence of HTN during pregnancy in blacks is consistent with previous reports [5–7]. The higher prevalence may be due to a predominance of socioeconomic and life-style factors, or to genetic differences in the two races. In a recent study, Irwin et al. [16] investigated a cohort of active duty military women and
showed an increased risk for pregnancy-induced HTN and preeclampsia in black women. Our study did not address the possible reasons for a higher prevalence of HTN in blacks. The principal part of this investigation was directed toward elucidating the racial differences in the outcome of hypertensive pregnancies. Our finding of greater risk for adverse outcome in white hypertensives as compared to blacks is intriguing. In our study, white hypertensives had a 250% greater reduction in birthweight of newborns as compared to black hypertensives. De Baun et al. [9] have shown that white women with pregnancy-induced hypertension are at a greater risk for delivering very-low-birth-weight infants than blacks. This racial difference, however, was not observed with other medical complications during pregnancy like diabetes mellitus and urinary tract infections. Pietrantoni et al. [1], on the contrary, reported a higher rate of intrauterine growth retardation in black hypertensives. We considered the possibility of differences in the type of HTN afflicting pregnant women of the two races as contributing factors. In our study, black hypertensives had a
HYPERTENSION DURING PREGNANCY
similar proportion of women with chronic hypertension (33.0%) as compared to whites (32.9%). This is, therefore, unlikely to be the explanation for the greater effect in whites. Chronic hypertension superimposed by preeclampsia represents a high risk group with high complication rate. However, our study was unable reliably to identify women falling into this category, thus limiting our ability to quantitate morbidity and mortality in this group. In two large epidemiological studies, when other risk factors for cardiovascular disease were taken into account, elevated blood pressure in male whites carried no worse cardiovascular prognosis [17,18]. Additionally, in a study based upon a work-site program of blood pressure control, Ooi et al. [19] showed that given access to adequate antihypertensive treatment, there were no racial differences in the outcome of hypertensives. However, none of these studies included pregnant women. In our study, it is unclear why white hypertensives were more likely to have adverse outcomes in spite of having received greater prenatal care than black hypertensives. We recognize the problem of ascertainment bias that accompanies retrospective studies such as ours. Every effort was made in this study to minimize this problem through periodic reviews of charts to validate abstracted data. Still, improper classification of women with overlapping hypertensive conditions may have altered the results. Further, women who had no prenatal care, or care starting late in gestation, may have been misclassified. Finally, hypertension, like other forms of cardiovascular disease, is a complex mixture of genetic and environmental influences. The contribution of unmeasured confounders to the black-white differences observed in this study is unknown and needs further evaluation. Our study does not address the issue of why black women are more likely to have hypertension during pregnancy. Our study does show that white women have lower baseline rates for all of the adverse pregnancy outcomes compared to black women, but HTN increases the risk of adverse outcomes proportionately more for white women than for black women. Further studies are necessary to confirm our findings and to understand the reasons for the racial differences in the impact of HTN on pregnancy outcome. ACKNOWLEDGMENTS The authors are grateful to Drs. Kevin Sullivan and Francine Dykes for their critical review of this manuscript, and to Ms. Barbara Reynolds for her secretarial assistance. REFERENCES 1. Pietrantoni M, O’Brien WF: The current impact of the hypertensive disorders of pregnancy. Clin Exper Hypertension 16:479–492, 1994.
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