The purpose of this study is to determine whether Valacyclovir treatment, administered during pregnancy after proven primary maternal Cytomegalovirus (CMV) infection, reduces fetal transmission rates and prevents fetal injury in cases of fetal infection.

A randomized, double-blind, placebo-controlled study.

Participants: Pregnant women over 18 years of age with serologically proven, primary CMV infection during the first trimester

Intervention: After informed consent and randomization, participants in the treatment group will receive Valacyclovir at a dose of 8 g/d. Participants in the control group will receive the same amount of daily pills containing placebo. Treatment will continue until amniocentesis, which will determine if the fetus was infected.

Inclusion Criteria:

• Pregnant women over 18 years of age with serologically proven, primary CMV infection during the first trimester of pregnancy or periconceptionally

Exclusion Criteria:

• Patients with preexisting liver disease, renal dysfunction, bone marrow suppression or sensitivity to Acyclovir will be excluded from the study - as will patients receiving any antiviral therapy prior to the study.