according to a study published in the Sept. 2 issue of the New England Journal of Medicine, Reuters Health reports.

SIDS, also known as crib death or cot death, is a leading cause of infant death in developed countries, according to Reuters Health.

Alpha-fetoprotein levels in the blood of pregnant women indicate how well the placenta is functioning and are often measured to determine if a fetus will be born with birth defects, according to Dr. Gordon Smith, the study's lead researcher and a professor of obstetrics and gynecology at the University of Cambridge in the United Kingdom.

High AFP levels are a sign that the placenta is not working "optimally," according to Reuters Health. Smith and colleagues analyzed data from AFP tests performed between 1991 and 2001 in Scotland on women in their second trimester of pregnancy.

Of the total 214,532 live births, 114 SIDS deaths were recorded, resulting in a rate of 5.3 SIDS deaths per 10,000 live births. The researchers found that women with the highest levels of AFP were twice as likely to have an infant die from SIDS than women with the lowest levels (Gale, Reuters Health, 9/1).

"This is significant research," Smith said, adding, "But it is not significant because we will be able to offer women a diagnostic test, it is significant because it helps us understand the causes of cot death. It also shows conditions in pregnancy are a major determinant of the vulnerability of the baby to cot death."

Smith added that the risk of SIDS was still "relatively low." The women in the study with the highest levels of AFP had infants with a one in 1,000 chance of SIDS, compared with an average risk of one in 2,000, according to BBC News (BBC News, 9/2).