Prenatal Treatment of Congenital Cytomegalovirus Infection With Letermovir Versus Valaciclovir

Inclusion Criteria: * Pregnant woman ≥ 18 years old, * CMV infection in the 1st trimester * with an infected fetus at 15 -28 weeks (positive CMV PCR in the amniotic fluid) With a fetus presenting without any severe cerebral ultrasound feature (ventriculomegaly ≥15 mm, hydrocephalus, periventricular hyperechogenicity, microcephaly\<-3SD, vermian hypoplasia, porencephaly, lissencephaly, corpus callosum dysgenesis, cystic leukomalacia) * affiliation to a social security regime//health insurance * Given consent for the study * Patient must be able and willing to comply with study visits and procedures Exclusion Criteria * Participation to another interventional drug trial (category 1) * Subject protected by law under guardianship or curatorship * Maternal CMV infection after 15 weeks' * Creatinine clearance \<50 ml/mn/1,73m² * Liver insufficiency (Child Pugh grade C), AST, ALT 5 x ULN, bilirubin 2 x ULN. * Woman with known allergy to Letermovir or Valaciclovir * Contraindication for the administration of Letermovir and Valaciclovir listed in the SmPC of Prevymis® and Zelitrex® * Women with hypersensitivity to aciclovir * Concomitant administration of St John's wort * Woman treated by pimozide, ergot alkaloids, dabigatran, atorvastatin, simvastatin, rosuvastatin, pitavastatin or cyclosporin. * Woman with hereditary intolerance to galactose, with lactose lapp deficiency, glucose or galactose malabsorption syndrome