The likelihood that a baby born in the U.S. will die within its first year is less than a third of what it was 50 years ago. But among mothers who were, themselves, born in the U.S., infant mortality rates are some 40 percent higher than for U.S.-born babies of non-native mothers.

Only Cuban and Puerto Rican mothers born outside of the U.S. had higher infant mortality rates than their counterparts who had been born here.

The new assessment, from a recent report [pdf] by the U.S. Centers for Disease Control and Prevention, assessed the number of infant deaths (averaged per 1,000 live births in 2007) of Asian, black, Central and South American, Cuban, Mexican, Puerto Rican and white mothers.

Mothers of African descent who were born in the U.S. had by far the highest infant mortality rates (13.37 deaths per 1,000 births). The lowest rates were among mothers of Asian or Pacific Island heritage who had been born abroad (4.25 per 1,000 births).

Of the 4.3 million children born in the U.S. in 2007, about 30,852 of them died before their first birthday (some 7.15 babies per 1,000)—a fraction of global infant mortality, which still hovers around 45 per 1,000 births. Infants are most likely to die within their first 27 days, and the most common causes of U.S. infant mortality were malformations, followed by low birth weight and pre-term delivery.

A previous study found that foreign-born mothers in New York City also had lower rates of infant mortality than mothers born stateside. The paper's authors, Kai-Lih Liu and Fabienne Laraque (both of the New York City Department of Health), proposed that rather than the so-called healthy immigrant effect (which says that people who make the move to the U.S. are healthier than average), other maternal health factors—including diet, prenatal care, long-term stressors and exposure to risky environments—are likely contributing more widely to these trends in infant survival.

"Better pre-pregnancy health, reduction of unintended pregnancy, consultation on infant care and safety need to be specifically addressed" in certain populations, Liu and Laraque noted in their 2006 Journal of Immigrant and Minority Health paper. "Culturally sensitive training for health care providers and customized pre-conception and maternal-infant health programs may be helpful to improve access and quality of reproductive and perinatal health care for disadvantaged mothers," they wrote.

And a recent report from the Institute for Health Metrics and Evaluation at the University of Washington shows that women with more years of education also have lower rates of child mortality.

Image courtesy of Wikimedia Commons/Melimama