Prenatal diagnosis of congenital varicella infection

Fourteen fetuses at risk of Varicella-Zoster virus (VZV) infection underwent prenatal diagnosis at 10-24 weeks' gestation by a combination of chorionic villus sampling, amniocentesis, and fetal blood sampling. Polymerase chain reaction (PCR) was done on fetal and placental tissues, using primers which define a 221 bp region of the gene coding for the 44 kD protein of VZV. Positive cases were further analysed by dot blot hybridization, using radiolabelled DNA probes corresponding to the Hind III fragment VZV genome. The rate of placental/fetal infection was 36 per cent (5/14 fetuses: 2/11 in the first and 3/3 in the second trimester). At post-mortem examination, two aborted fetuses had hydrocephaly and VZV DNA was found in most of the examined tissues. The nine women who tested negative at prenatal investigation delivered healthy neonates whose VZV-specific IgM antibody titres were negative and none of them developed herpes zoster infection. In view of the high frequency of fetal VZV infection and the reported low rate of malformations, the role of invasive prenatal diagnosis in women who acquire the infection in the first half of gestation is mainly that of reassurance when the test is negative.