CMV Infected Fetuses

The investigators' hypothesis is that maternal treatment with Letermovir will inhibit fetal CMV replication better than Valaciclovir in infected fetuses and lead to a higher proportion of negative CMV PCR at birth in neonatal blood collected in the first day of life or in cord blood in case of termination of pregnancy (TOP). The main objective is to demonstrate that Letermovir administered to women carrying a CMV infected fetus following a maternal infection of the first trimester increases the proportion of neonates with a negative CMV PCR in neonatal blood collected in the first day of life or in cord blood in case of termination of pregnancy (TOP) compared to Valaciclovir. In each group , the proportion of asymptomatic neonates and the number and type of long-term sequelae at 2 years will also be assessed and compared.