Correspondence
The Racial Disparity in Very Low Birth Weight
N Engl J Med 1993; 328:285-286January 28, 1993
- Article
To the Editor:
Dr. Kempe and her associates have presented a thoughtful analysis of infants with very low birth weight (Oct. 1 issue)1. Their study design failed to consider three important factors crucial to an analysis of intrauterine growth.
First, although race-specific differences in birth weight are well established, they may be confounded by definitions of race. The authors defined the race of the child as that of the mother. National rates for birth weight are reported according to both the race of the mother and that of the child. Depending on which is used, the rates can differ.
Second, the failure to exclude multiple births from the study sample biases the results. Although multiple births represent only 2 percent of all live births in the United States, they account for a disproportionate number of births involving low or very low birth weight. As compared with the risk among singletons, the relative risk of low birth weight is 10.3 for twins and 19.4 for three or more infants; the relative risk of very low birth weight is 9.6 for twins and 32.7 for three or more infants2.
Third, the maternal anthropometric characteristics and nutritional status were not described. After the length of gestation, maternal weight gain accounts for the largest proportion of variation in birth weight; pregravid weight has the next largest effect3. White and black women differ in pregravid weight and weight gain during pregnancy. The incidence of overweight is 1.8 times higher among black women than among white women (44 percent vs. 25 percent), and the incidence of severe obesity is almost twice as great (19 percent vs. 10 percent)4. Black women are more likely to be advised to restrict their weight gain, and to gain less during pregnancy. Data from national surveys showed that 26 percent of married white women were advised to limit their weight gain to 21 lb (9.5 kg), as compared with 34 percent of married black women5. An actual gain of at least 21 lb occurred in 22 percent of white women and 33 percent of black women6. Each complication of pregnancy cited by Kempe et al. has associated nutritional components. Race may be a confounding factor between dietary intake, nutritional status, and the rate and pattern of weight gain during pregnancy and birth weight, preceding or compounding medical factors ultimately leading to very low birth weight.
We disagree with the authors' conclusions that the rate of very low birth weight is not amenable to individual clinical interventions; nutrition therapy -- specifically, greater maternal weight gain -- has proved effective in increasing birth weight. As one of the health objectives of the nation for the year 2000, adequate maternal nutrition is a national priority and should be considered in any study evaluating intrauterine growth.
6 ReferencesBarbara Luke, Sc.D., M.P.H., R.D.
Rush Medical CollegeMaureen Murtaugh, Ph.D., R.D.
College of Health Sciences, Rush University, Chicago, IL 606121
Kempe A ,Wise PH ,Barkan SE , et al. Clinical determinants of the racial disparity in very low birth weight. N Engl J Med 1992;327:969-973
Full Text | Web of Science | Medline2
Luke B ,Keith L . The contribution of singletons, twins, and triplets to low birthweight, infant mortality and handicap in the United States. J Reprod Med 1992;37:661-666
Web of Science | Medline3
Niswander K ,Jackson BC . Physical characteristics of the gravida and their association with birth weight and perinatal death. Am J Obstet Gynecol 1974;119:306-313
Web of Science | Medline4
Najjar MF, Rowland M. Anthropometric reference data and prevalence of overweight: United States, 1976-80. Vital and health statistics. Series 11. No. 238. Washington, D.C.: Government Printing Office, 1987. (DHHS publication no. (PHS) 87-1688.)
5
Taffel SM ,Keppel KG . Advice about weight gain during pregnancy and actual weight gain. Am J Public Health 1986;76:1396-1399
CrossRef | Web of Science | Medline6
Taffel SM. Maternal weight gain and the outcome of pregnancy: United States, 1980. Vital and health statistics. Series 21. No. 44. Washington, D.C.: Government Printing Office, 1986. (DHHS publication no. (PHS) 86-1922.)
Author/Editor Response
The authors reply:
To the Editor: We appreciate the thoughtful points raised by Drs. Luke and Murtaugh. Although we agree that the distinction between the race of the mother and that of the infant is important, most studies of adverse birth outcomes,1,2 as well as national vital-statistics reports,3 have used maternal race to represent race-related influences on the intrauterine environment. We used maternal race since our focus was on the pathologic conditions associated with the delivery of very-low-birth-weight infants, conditions more likely to reflect the social and medical experiences of the pregnant women.
We did not exclude multiple births because we wished to describe the spectrum of conditions associated with all very-low-birth-weight infants. Therefore, in comparing the racial distributions of associated conditions, we used the number of pregnancies as the unit of analysis, even if delivery resulted in multiple births. Although minor differences in multiple gestations between racial groups and study sites were noted, controlling for this factor did not alter the results of our analyses.
The purpose of our study was not to analyze all influences on the disparate rates of very low birth weight, but to document the clinica expression of these interactive influences in total populations. We agree that nutritional status and weight gain can influence birth outcomes, but maternal weight gain may reflect the effect of other factors, such as chronic medical conditions, smoking, or drug use. Our intention was to help guide the exploration of precursor interactions by documenting the clinical outcomes that they ultimately produce. It is also important to recognize that factors that may influence mean birth weight or even rates of low birth weight may not necessarily be relevant to the development of the pathologic conditions resulting in very low birth weight4.
We agree that improved maternal nutrition is important in preventing very low birth weight. However, it is best advocated as a component of comprehensive initiatives that link the improvement of birth outcomes to more fundamental efforts to improve the general health of black women in the United States.
4 ReferencesAllison Kempe, M.D., M.P.H.
Paul H. Wise, M.D., M.P.H.
Harvard Institute for Reproductive and Child Health, Boston, MA 021151
Lieberman E ,Ryan KJ ,Monson RR ,Schoenbaum SC . Risk factors accounting for racial differences in the rate of premature birth. N Engl J Med 1987;317:743-748
Full Text | Web of Science | Medline2
Kleinman JC ,Kessel SS . Racial differences in low birth weight: trends and risk factors. N Engl J Med 1987;317:749-753
Full Text | Web of Science | Medline3
National Center for Health Statistics. Health, United States, 1991. Hyattsville, Md.: Public Health Service, 1992. (DHHS publication no. (PHS) 92-1232.)
4
Levkoff AH ,Westphal M ,Miller MC III ,Michel Y . Maternal risk factors in infants with very low birth weight. Obstet Gynecol 1982;60:612-616
Web of Science | Medline
- Citing Articles (1)
Citing Articles
1
Eve C. Feinberg, Frederick W. Larsen, William H. Catherino, Jun Zhang, Alicia Y. Armstrong. (2006) Comparison of assisted reproductive technology utilization and outcomes between Caucasian and African American patients in an equal-access-to-care setting. Fertility and Sterility 85:4, 888-894
CrossRef
