One reason for the high rate of premature births and infant mortality among blacks is that a greater proportion of black women are anemic than whites, Harvard researchers said in today's New England Journal of Medicine.
In another study in the journal, researchers reported that teen-age pregnancy, usually counted as an important factor in infant mortality, is not a major contributor to the high rates among blacks. Black infants are twice as likely as whites to die.
The Harvard researchers said they discovered that black women have consistently lower levels of oxygen-carrying red blood cells, and that these low levels are linked to premature births and, thus, to the risk of infant death.
Other factors, such as low level of education and poverty, were also found to be linked to premature birth.
But when white and black women with the same education and poverty were compared, almost twice as many black women had low "hematocrit" levels -- a count of blood cells.
Dr. Ellice Lieberman of Harvard and the Brigham and Women's Hospital in Boston, the leader of the Harvard group, said it is not known why a higher proportion of the 1,365 black women in the study had low blood counts, but she said it may be either genetic or because of environmental factors such as nutrition or infection.
In a separate study at the National Center for Health Statistics, researchers reported that they were surprised to find that the impact of younger, poorer and less educated mothers among blacks was not enough to explain the high infant mortality rate among blacks.
Joel Kleinman and Samuel Kessel at NCHS studied the birth records of nearly 2.5 million black and white women. Three factors -- being young, unmarried and having little education -- all appeared to contribute to high rates of low birth weights.
But all the factors together did not explain the difference between the races, the researchers wrote.
The wide difference in low birth weights occurred even among blacks and whites who were married college graduates.
The researchers said the study indicates a need to look beyond traditional risk factors to explain low birth weights and infant mortality among blacks.