updated 3/6/2006 10:30:15 AM ET 2006-03-06T15:30:15

Pregnant women who get West Nile virus likely will have normal babies, although a small risk of birth defects can’t be completely ruled out, according to the first published report from a multistate registry.

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Researchers at the federal Centers for Disease Control and Prevention called their report “somewhat reassuring” but said pregnant women still should be especially careful to follow precautions, including staying indoors when mosquito activity is high and wearing repellent during mosquito season.

Of 72 infants in 16 states whose mothers had West Nile during pregnancy, only three had problems that might have been linked with exposure to the virus before birth, according to 2003-2004 data from the registry.

Two had abnormally small heads and one was born with an extra toe. In all three cases, the mothers had fevers but otherwise relatively mild cases of West Nile.

One of the small-headed infants had severe birth defects and died three days after birth, but the other appeared to grow out of the problem and was developing normally by age 1.

None of the infants studied “had conclusive laboratory evidence” of developing West Nile virus infection from their mothers, although scientists are uncertain how effective current tests are at detecting West Nile infection at birth, according to the report, being published Monday in the March edition of Pediatrics.

Because of circumstantial evidence, “we couldn’t say with confidence they (birth problems) were not caused by West Nile virus,” said CDC researcher and co-author Daniel O’Leary.

That evidence includes timing of the mothers’ infections. The mother of the extra-toe baby had West Nile fever early in pregnancy, when development of fingers and toes occurs. The other two mothers got sick during mid-pregnancy.

Other factors examined
Seven, or 10 percent of the infants, had major birth defects including Down syndrome and cleft palate, about double the rate in the general population, but prevalence of miscarriages and premature births was lower than in the general population. However, the researchers believe only the three cases might be linked to the virus.

CDC-funded research is investigating whether any of the women had other factors that might have increased their risks for having children with birth defects, O’Leary said.

The CDC collects nationwide data on pregnant women infected with West Nile disease, the mosquito-borne virus that has been reported in humans in at least 42 states.

The states involved in the new report are Arizona, Colorado, Idaho, Illinois, Kansas, Louisiana, Minnesota, Montana, Nebraska, New York, North Dakota, Oklahoma, Pennsylvania, South Dakota, Texas and Wyoming.

Most infected people never get sick, but up to about 20 percent develop mostly mild flu-like symptoms. Severe symptoms, including sometimes fatal brain inflammation, are rare. Since 1999, when the virus first appeared in this country, 782 West Nile deaths have been reported nationwide.

Dr. Shari Goldman, an obstetrician affiliated with Chicago’s Northwestern Memorial Hospital, said none of her pregnant patients have developed West Nile though some have asked how they can avoid the disease.

“I raise it as a concern that they should think about, however I do not want to alarm my patients because the risk of them contracting West Nile virus is low,” Goldman said.

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