Objective: Varicella, resulting from primary infection by varicella zoster virus, carries a risk of severe congenital varicella. Prenatal diagnosis is rarely applied because methods remain to be validated.
Study design: From 1989 to 1994, 107 women contracted clinical varicella before 24 weeks of pregnancy. Amniocentesis was performed in all cases, with simultaneous fetal blood sampling in 82 cases. Virus was detected in amniotic fluid by cell culture inoculation and polymerase chain reaction. Fetal blood was tested for anti-varicella zoster virus immunoglobulin M.
Results: Of the 107 amniotic fluid samples tested, nine of 107 (8.4%) were positive by polymerase chain reaction, but only two of these (1.8%) were positive in cell culture; none of the blood samples from infected fetuses were positive for specific anti-varicella zoster virus immunoglobulin M. The outcome of 99 pregnancies was fully documented.
Conclusion: The risk of transplacental passage before 24 weeks of pregnancy was 8.4% in our series. The risk of congenital varicella is 3 in 107 (2.8%) and that of isolated postnatal varicella zoster infection is 3 in 78 (3.8%). Polymerase chain reaction is more sensitive than cell culture for the detection of varicella zoster virus in amniotic fluid.