The prevalence of congenital varicella syndrome after a maternal infection, but before 20 weeks of pregnancy: a prospective cohort study.

OBJECTIVE: To describe the prevalence of congenital varicella syndrome (CVS) within the population of presumably infected pregnant women.

METHODS: From 1993 to 2006, all women who presented vesicular rash or a suspicious contact were referred and evaluated in a special unit at our center. Those with residual immunity or were serologically negative were precluded from this study. Positive IgM cases underwent monthly ultrasound scans (US), fetal blood (FB) sampling (including IgM anti VZV and virus culture). Amniotic fluid sample for PCR was added to the diagnosis of positive IgM cases after 1997.

RESULTS: A total of 276, of the 566 consulted women, tested positive for IgM anti VZV. Seventeen (6%) were excluded because of an unadvised termination of pregnancy and seven (2.55%) miscarried. Only seven (2.7%) were considered highly likely to have a VZV fetal infection. One case showed positive IgM in FB but developed normally. Another fetus showed positive PCR and infection was confirmed post TOP. Four cases that underwent TOP and histochemistry confirmed no more cases. Complete post-natal follow-up was carried out. The asymptomatic infected child grew healthy until the completion of screening tests when it reached 5 years old.

CONCLUSION: The fetal infection rate in this cohort was 0.8%, but the best expected prevalence of CVS, according to our findings, should be 0.39% among infected women. This data should be considered and used during parental counselling.