A 26-year-old primigravida at 14 weeks gestation is found to have CMV IgM positive and CMV IgG positive. IgG avidity testing shows high avidity anti-CMV IgG. The best interpretation is:

• A Primary CMV infection acquired during this pregnancy, with high fetal transmission risk
• B Reactivation with guaranteed vertical transmission requiring termination of pregnancy
• C Congenital CMV infection of the fetus confirmed by maternal serology
• D Past CMV infection; the positive IgM is likely persistent or non-specific, and recent primary infection is unlikely ✓

Explanation

IgG avidity matures over weeks to months after primary infection, so high avidity IgG indicates infection remote in time. When combined with a positive IgM, high avidity favours persistent IgM from past infection or non-specific reactivity rather than recent primary infection, which carries the highest fetal risk. Congenital CMV is diagnosed by testing the neonate, not the mother.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.