WEDNESDAY, Sept. 1, 2004 (HealthDayNews) -- The mystery of sudden infant death syndrome (SIDS) may have gotten a little less murky: British researchers say a high level of a protein in a developing fetus corresponds with a nearly threefold increased risk of SIDS during infancy.
The protein, called alpha-fetoprotein (AFP), is already linked to heightened risks for congenital abnormalities and stillbirth, but experts say it's too early to say if it might help cause SIDS, too.
Nevertheless, "the results indicate that the risk of SIDS is partly determined by conditions in the womb," researchers led by Dr. Gordon C.S. Smith, a professor of obstetrics and gynecology at Cambridge University, said in a prepared statement. They published their findings in the Sept. 2 issue of the New England Journal of Medicine.
SIDS remains the leading cause of death for U.S. children in their first year of life, with about 2,500 deaths annually attributed to this type of sudden, unexplained event. However, the overall U.S. rate for deaths due to SIDS dropped by 50 percent starting in the early 1990s, largely due to "Back to Sleep" public education campaigns that urged parents to place babies on their backs at sleep time.
Too many babies continue to succumb to SIDS, however. Looking for other factors that might raise the risk, Smith's team focused on AFP as a possible culprit.
AFP is a protein produced naturally by the developing fetus, for reasons that remain unknown. What is known, however, is that AFP has strong ties to stillbirth and congenital abnormalities, according to experts. In fact, doctors routinely test for high maternal blood levels of AFP during pregnancy, to help spot birth defects early in gestation.
It seemed plausible that AFP might have links to SIDS in infancy, too, the researchers explained, "although no one had looked at this before."
In the study, Smith's team pored over hospital data on more than 214,500 live births in Scotland from the 1980s through 2001, including information on maternal AFP blood levels assessed during the second trimester of pregnancy.
According to the data, 114 of the Scottish newborns went on to die of SIDS during their first year of life.
"The study showed that the risk of SIDS was three times higher among women who were in the top 20 percent of [second-trimester] AFP levels compared with those in the bottom 20 percent," Smith's team reported. "This was partly, but not completely, explained by the fact that these women gave birth to babies which were smaller."
The British researchers stressed that the findings only point to an association, not a causal relationship, between high levels of AFP and SIDS. But they theorize that increases in AFP may point to an inefficient or poorly functioning placenta, which is the prime source of oxygen and nutrients for a fetus.
"This leads to poor growth, to an increased risk of early birth, and may also lead to effects on the control of breathing, which could lead to an increased risk of SIDS," they speculated.
Dr. Michael H. Malloy, a professor of pediatrics at the University of Texas Medical Branch at Galveston and the author of an accompanying commentary, said it's far too early to draw any firm conclusions from the findings.
"It's uncertain as to how, biologically, this would be plausible," he said. "At this point, I don't know that there's a great deal of biology to support whether it [SIDS] is growth-related."
And he pointed out that other risk factors, such as parental smoking, might help explain many SIDS cases. "These things continue to turn up, and they are much higher, in terms of relative risk," he said.
High maternal AFP levels in mid-pregnancy shouldn't be cause for alarm among prospective parents, the British researchers added.
"The association is not sufficiently strong for the test to be a useful predictor [of SIDS risk]," they pointed out. Furthermore, "SIDS is rare, affecting about one in 2,000 births. Even [babies] with a three times increased risk are more than 99.9 percent likely to survive without SIDS."
In the meantime, they wrote, "all the previous advice about sleeping position and smoking still stands. The environment in which the baby sleeps is crucial. What the present study shows is that the vulnerability of the baby to a bad environment is determined partly in the womb. But a bad sleeping environment can harm any baby."
More information
For more on SIDS, visit the Nemours Foundation.
