NEW YORK (Reuters Health) - Maternal urinary tract colonization or infection is associated with a reduced risk of sudden unexplained intrauterine death (SUID), according to a report published in the November issue of Obstetrics and Gynecology.

SUID may be caused by bacteria in the vaginal canal that ascend into the uterus, causing chorioamnionitis and, ultimately, fetal death, lead author Dr. J. Frederik Froen and colleagues, from the University of Oslo in Norway, note.

The reason why maternal urinary tract infections (UTIs) may protect against SUID is unclear, but the authors offer one possible explanation.

When bacteria such as Escherichia coli and enterococcus are present in the vagina and uterus, they are weak stimulators of a maternal antibody response, the researchers note. As such, the amount of antibody passed to the fetus is low, leaving the fetus relatively unprotected against intrauterine infections.

The bacterial strains responsible for vaginal and uterine colonization are often the same strains that cause UTIs. However, when such strains are present in the urinary tract, a vigorous maternal antibody response occurs. Passage of these high antibody levels to the fetus may protect the fetus against future, potentially lethal intrauterine infections, the authors postulate.

The current findings are based on a study of 76 cases of SUID, 165 cases of explained stillbirth, and 582 normal births that were recorded in Oslo between 1986 and 1995.

The researchers found that maternal urinary tract colonization or infection was associated with a 71% reduction in the risk of SUID. In contrast, insufficient physiologic hemodilution during pregnancy was a strong risk factor for SUID. Specifically, women whose lowest hemoglobin level was > 13 g/dL were 9.5 times more likely to experience SUID than women with lower values.

"These findings may shed new light on our understanding of mechanisms involved in SUID," the researchers point out. "If protection against infection gives protection against SUID, undetected subclinical infections could be involved."

Obstet Gynecol 2002;100:909-915.

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