Maternal blood test may help predict SIDS

During pregnancy, a blood test called alpha-fetoprotein can determine a woman's risk of having a child with birth defects. Now, new research suggests that this test can also predict a deadly problem that occurs after birth - sudden infant death syndrome (SIDS).

The findings suggest that the vulnerability of an infant to environmental factors is determined to a "significant extent by conditions in the womb," lead researcher Dr. Gordon C. S. Smith, at Cambridge University in the UK, and his team note in The New England Journal of Medicine.

The authors point out that despite effective public health campaigns, SIDS is still the single most important cause of infant death in the industrialized world.

"Many people have suggested that SIDS has similarities with unexplained stillbirth," Smith said in an interview with Reuters Health. "Alpha-fetoprotein is a good predictor of unexplained stillbirth. If the conditions are related, one would expect to see an association between alpha-fetoprotein and SIDS. "

To look for a possible link, Smith's group analyzed data from women who had given birth in western Scotland between 1991 and 2001. A total of 214,532 live births were recorded, among which there were 114 SIDS deaths, yielding a rate of 5.3 SIDS deaths per 10,000 live births. Alpha-fetoprotein tests had been performed during the second trimester of pregnancy.

Women with the highest alpha-fetoprotein levels were twice as likely to have an infant who died from SIDS than women with the lowest levels.

Alpha-fetoprotein is a marker of how well the placenta is functioning, Smith explained. "It is a protein that circulates in the blood of the baby and crosses the placenta." High levels of this protein in the mother indicate the placenta is not functioning optimally.

However, in a related editorial, Dr. Michael H. Malloy, at University of Texas Medical Branch, Galveston, comments that "the clinical importance (of a high alpha-fetoprotein level), relative to other demographic and behavioral risk factors...remains uncertain."

Smith also noted that "alpha-fetoprotein is not a predictive diagnostic test," and that women with elevated alpha-fetoprotein levels should not be concerned that their infant is at high risk of SIDS. In the current study, the rate of SIDS among women with the highest alpha-fetoprotein levels was still very low-just 7.5 cases per 10,000 live births.

Smith added that his group is now conducting studies in animals to better understand how problems in the womb can affect how the baby responds to stress after birth.

SOURCE: The New England Journal of Medicine, September 2, 2004.