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Investigators find a correlation between low birth weight (weighing less that 5 pounds, 8 ounces at birth) and higher prevalence of asthma among African-Americans in a study published in this month's Annals of Allergy, Asthma & Immunology, the scientific journal of the American College of Allergy, Asthma and Immunology (ACAAI).

"Our observation in middle-income, racially-diverse schoolchildren suggests that higher rates of asthma are associated with low birth weight in African-Americans," said Christine L. M. Joseph, Ph.D., Henry Ford Health System, Detroit. "We found that 30 percent of the racial difference in prevalence of asthma is explained by low birth weight.

The study population from a multi-ethnic suburb of Detroit consisted of 126 children, 70 percent of which were African-American. Asthma and low birth weight were reported more frequently by African-Americans (asthma 12.5 percent vs. 5.3 percent; low birth weight 16.6 percent vs. 3.9 percent).

Estimates for pediatric asthma prevalence rates are two to three times higher for African-Americans compared to other races. Studies indicate African-American women are two to three times more likely to deliver a baby of low birth weight (5.5 pounds or less at birth).

Findings are supported by previous studies, including a large cross-sectional analysis which identified a strong independent association between low birth weight and asthma.

"The relationship between asthma and low birth weight has been explored by investigators in different ways, looking at variables including birth weight, prematurity and subsequent diagnosis of asthma. But we have not identified whether the mechanism is determined by prenatal factors or medical procedures required for the baby," Dr. Joseph said.

According to the report, prenatal factors that could be attributable to smaller lung size or pulmonary impairment including smoking during pregnancy, lower respiratory tract illness, or poor maternal nutrition. Medical procedures, such as mechanical ventilation, may also affect the lung to dispose the infant to asthma.

"Smoking cessation during pregnancy is an important method of reducing the risk of low birth weight," said Cheryl B. Prince, Ph.D., M.P.H., M.S.N., State MCH Epidemiologist, Hawaii Department of Health, Honolulu. "Since prematurity is highly correlated with low birth weight, reducing the rates of preterm delivery is desirable. However, preterm delivery prevention strategies are unclear and may be related to reducing risks of prenatal stress, depression and bacterial vaginosis among other things.

"Clearly, reducing the prevalence of asthma attributable to low birth weight will require collaborative efforts of the allergist, immunologist, pediatric and obstetric community to develop effective interventions," Dr. Prince said.

The investigators plan to recruit pregnant women for a larger study led by Christine C. Johnson, Ph.D. They will follow children from pregnancy through infancy to further investigate the relationship between low birth rate and asthma in African-Americans.

"Although I do not believe that a cause and effect relationship between low birth weight and asthma can be made from this study, the association is thought provoking and will hopefully encourage more women to get prenatal care to reduce the number of low birth weight infants," said allergist-immunologist Joan C. Gluck, chair, ACAAI Women's Health Committee, Miami. "It also underscores the risk associated with smoking during pregnancy.

"Since asthma is more common in African-American's, the increase may be due to a greater number of pregnant asthmatics in this group, with the disease possibly not well controlled. This would result in more low birth weight infants with a genetic predisposition to develop asthma.

"Once the prospective study is expanded to begin prenatally, this data can be collected and the children can be followed to see if there is a higher incidence of asthma with low birth weight regardless of a history of asthma in the mother or in the family," Dr. Gluck said.

The ACAAI is a professional medical organization comprised of 4,200 qualified allergists-immunologists and related health care professionals. The College is dedicated to the clinical practice of allergy, asthma and immunology through education and research to promote the highest quality of patient care.

* Joseph CLM, Ownby DR, et al. Does low birth weight help to explain the increased prevalence of asthma among African-Americans? Ann Allergy Asthma Immunol 2002; 88:507-512.

* Brooks AM, Byrd RS, Weitzman M, et al. Impact of low birth weight on early childhood asthma in the United States. Arch Pediatr Adolesc Med 2001;155:401-406.