CMV maternal infection in first trimester

For CMV, the use of high dose valaciclovir early on in pregnancy to those who

have been infected with CMV in the first trimester has been shown to reduce the

risk of transmission of CMV to the fetus (see https://pubmed.ncbi.nlm.nih.gov/37473793/).

We do a step-wise screening for CMV infection in the first trimester:

1. We start off with CMV IgM at about 12 weeks.

2. If positive, we check for CMV IgG.

3. If CMV IgG is positive, we check for CMV IgG avidity.

   1. If CMV IgG avidity is low, it indicates an infection in the last 3-4 months. There is then a risk for fetal CMV infection.

   2. If CMV IgG avidity is high, it indicates an infection > 4 months ago. The risk of congenital CMV infection to the fetus is then very small.

Amniocentesis from 17 weeks onwards can be performed to check if CMV particles can be found in the amniotic fluid. If CMV cannot be found in the amniotic fluid, it is very unlikely that the baby would suffer any major consequences from being exposed to maternal CMV infection during the first trimester. If CMV is found in the amniotic fluid, the fetus is confirmed to have fetal CMV infection. You should see a fetal medicine specialist to discuss this.