Chicago ? 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.

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 today 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.