Valaciclovir to prevent vertical transmission of cytomegalovirus after maternal primary infection during pregnancy: a randomised, double-blind, placebo-controlled trial

Lancet. 2020 Sep 12;396(10253):779-785. doi: 10.1016/S0140-6736(20)31868-7.


Background: Cytomegalovirus is a common congenital infection, with high morbidity after an early primary maternal infection. No effective means exist to prevent viral transmission to the fetus. We aimed to investigate whether valaciclovir can prevent vertical transmission of cytomegalovirus to the fetus in pregnant women with a primary infection acquired early in pregnancy.

Methods: This prospective, randomised, double-blind, placebo-controlled trial was done at the Infectious Feto-Maternal Clinic of Rabin Medical Center (Petach Tikvah, Israel). Pregnant women aged 18 years or older, with serological evidence of a primary cytomegalovirus infection acquired either periconceptionally or during the first trimester of pregnancy, were randomly assigned to oral valaciclovir (8 g per day, twice daily) or placebo from enrolment until amniocentesis at 21 or 22 gestational weeks. Randomisation was done separately for participants infected periconceptionally or during the first trimester and was done in blocks of four. Patients and researchers were masked to participant allocation throughout the entire study period. The primary endpoint was the rate of vertical transmission of cytomegalovirus. Statistical analyses were done according to per-protocol principles. The study was registered at, NCT02351102.

Findings: Between Nov 15, 2015, and Oct 8, 2018, we enrolled and randomly assigned 100 patients to receive valaciclovir or placebo. Ten patients were excluded, five from each study group; therefore, the final analysis included 45 patients (all singletons) in the valaciclovir group and 45 patients (43 singletons and two sets of twins) in the placebo group. In the valaciclovir group, including both first trimester and periconceptional infections, five (11%) of 45 amniocenteses were positive for cytomegalovirus, compared with 14 (30%) of 47 amniocenteses in the placebo group (p=0·027; odds ratio 0·29, 95% CI 0·09-0·90 for vertical cytomegalovirus transmission). Among participants with a primary cytomegalovirus infection during the first trimester, a positive amniocentesis for cytomegalovirus was significantly less likely in the valaciclovir group (two [11%] of 19 amniocenteses) compared with the placebo group (11 [48%] of 23 amniocenteses; p=0·020. No clinically significant adverse events were reported.

Interpretation: Valaciclovir is effective in reducing the rate of fetal cytomegalovirus infection after maternal primary infection acquired early in pregnancy. Early treatment of pregnant women with primary infection might prevent termination of pregnancies or delivery of infants with congenital cytomegalovirus.

Funding: None.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Antiviral Agents / adverse effects
  • Antiviral Agents / therapeutic use*
  • Cytomegalovirus Infections / transmission*
  • Double-Blind Method
  • Female
  • Humans
  • Infectious Disease Transmission, Vertical / prevention & control*
  • Medication Adherence
  • Pregnancy
  • Pregnancy Trimester, First
  • Prospective Studies
  • Time-to-Treatment
  • Valacyclovir / adverse effects
  • Valacyclovir / therapeutic use*


  • Antiviral Agents
  • Valacyclovir

Associated data