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Maternal AFP level associated with SIDS.

The risk of SIDS increased in a linear fashion in association with rising serum levels of maternal alpha-fetoprotein during the second trimester of pregnancy in a study of 214,532 Scottish women.

Tests for maternal serum alpha-fetoprotein (AFP) levels primarily are used to help diagnose fetal anomalies, especially neural tube defects, and can predict an increased risk for unexplained stillbirth, previous studies have shown. Women in the current study had elevated AFP levels with no fetal abnormalities. The results suggest that SIDS and unexplained stillbirth share common pathophysiologic components, Gordon C.S. Smith, M.D., reported (N. Engl. J. Med. 2004;351:978-86).

The current study linked prenatal and postnatal data on the women and their singletons, 114 of whom died of SIDS during the first year of life. The incidence of SIDS increased from 3 per 10,000 births among women with AFP levels in the lowest quintile to 8 per 10,000 births for women with AFP levels in the highest quintile, said Dr. Smith of Cambridge (England) University and his associates.

Earlier gestational age at delivery and lower infant birth weights also were associated with an increased risk for SIDS. After adjustment for these factors, the risk for SIDS increased 70% among women in the second-lowest and third-lowest quintiles of AFP levels, compared with women with the lowest AFP levels. The adjusted risk for SIDS increased 120% among women with AFP levels in the highest and second-highest quintiles, compared with those with the lowest AFP levels.

AFP contributes to oncotic pressure in the fetal circulation. Elevated AFP levels without fetal abnormalities are thought to indicate defects in placental function. These suboptimal intrauterine conditions may result in altered cardiorespiratory control that could predispose infants to SIDS, Dr. Smith speculated, but this hypothesis needs further study.

AFP is a nonspecific marker of fetal and placental dysfunction, however, and may be associated with other causes of death besides SIDS, Michael H. Malloy, M.D., said in an essay in the same issue (N. Engl. J. Med. 2004;351:957-9). The clinical relevance of the study's findings "remain uncertain," said Dr. Malloy, a pediatrician at the University of Texas Medical Branch, Galveston.

The association between elevated AFP levels and SIDS is not necessarily predictive and must be verified by further research, Fern Hauck, M.D., told this newspaper in a phone interview. "I would really exercise some caution at this point" and avoid testing AFP solely to assess SIDS risk or frightening mothers with high AFP levels by telling them to monitor their babies for SIDS, said Dr. Hauck, a family physician and SIDS researcher at the University of Virginia, Charlottesville.

SIDS is the greatest single cause of death in the postnatal period (1 month to 1 year) in the industrialized world, affecting approximately 2,200 U.S. infants each year, but "it's still a relatively rare occurrence, so even twice the risk is still fairly low. We need to have more information before we draw too many conclusions" about the study's results, she said.

The possibility that viruses are associated with SIDS is being examined in a study that Milwaukee County Medical Examiner Jeffrey Jentzen, M.D., and the Milwaukee Health Department's chief virologist, Gerald Sedmak, Ph.D., have been doing to search for viruses in reported SIDS cases. Two Wisconsin infants who died from SIDS were found to have a virus recently discovered in Japan--human parechovirus 3.

SIDS investigations do not routinely look for viral infection. "We don't know if these were incidental findings, because viruses are common in small children, or if they played a causative role," said Dr. Hauck. She is a member of a panel of experts that is designing a more user-friendly SIDS investigative report form for the Centers for Disease Control and Prevention.

Mild upper respiratory infection (which can be caused by a number of viruses) often precedes SIDS, she noted. Most experts consider infections to be one of many factors that might contribute to SIDS in already vulnerable infants, along with prenatal factors such as maternal smoking and environmental factors such as soft mattresses, overheating, or prone sleeping position.

Neither the detection of the new viruses in two SIDS cases nor the reported link between maternal AFP levels and SIDS qualify as breakthroughs in understanding SIDS, she said.
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Title Annotation:Clinical Rounds
Author:Boschert, Sherry
Publication:Pediatric News
Geographic Code:1USA
Date:Nov 1, 2004
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