Cytomegalovirus (CMV) is a highly common virus belonging to the herpes family; most adults have been infected by age 40, often without knowing it. Once infected, the virus remains dormant within the body for life. A positive test result for Immunoglobulin G (IgG) during pregnancy indicates this prior exposure and the presence of protective antibodies. This finding means the body has already developed an immune response, focusing on the low risk of recurrent infection to the developing baby.
Understanding the IgG Positive Result
The laboratory finding of a positive CMV IgG test signifies that the body encountered the virus in the past. Immunoglobulin G antibodies are the long-term memory of the immune system, appearing weeks after initial exposure and persisting indefinitely. This antibody presence confirms a baseline level of immunity, offering substantial protection against the virus. This IgG positive status is distinct from a positive Immunoglobulin M (IgM) result, which typically indicates a very recent or primary infection, which carries the highest risk for the fetus. While IgG indicates past exposure, the virus can occasionally reactivate or the mother can be re-exposed to a different strain, leading to a recurrent infection.
Fetal Risk in Recurrent CMV Infection
The implications of an IgG positive result are significantly less concerning than those following a primary CMV infection during pregnancy. Primary infection transmits to the fetus in 30% to 40% of cases, but the rate of transmission during a recurrent infection is dramatically lower, often cited as less than 1% or 2%. This difference is related to the maternal immune response, as pre-existing antibodies cross the placenta and provide protection to the fetus. Even when transmission occurs, the fetal consequences are usually milder. Cases resulting from recurrent infection rarely show symptoms at birth, compared to primary infection which can lead to symptomatic disease in about 10% of infected infants.
Clinical Monitoring and Diagnostic Steps
For a pregnant individual with an established IgG positive status, clinical management focuses on surveillance rather than immediate intervention. Regular prenatal care will typically include serial ultrasounds to monitor the fetus for any signs of complications associated with the virus. These scans look for subtle indicators such as intrauterine growth restriction, microcephaly, or intracranial calcifications. If the timing of the initial infection is uncertain, or if there are any concerning findings on the ultrasound, further diagnostic steps may be considered. The most definitive prenatal test is amniocentesis, which checks for the presence of CMV DNA in the amniotic fluid. This procedure is generally performed after 21 weeks of gestation and at least eight weeks following the suspected maternal infection.
Treatment Considerations
Antiviral treatment options during pregnancy are limited and are not standard practice for recurrent CMV infection. Hyperimmune globulin (HIG) is a treatment that involves infusing concentrated CMV-specific antibodies. Its use is mainly reserved for cases of confirmed primary infection with evidence of fetal involvement.
Practical Prevention Measures
Even with a positive IgG result, adopting specific hygiene practices minimizes the potential for viral reactivation or re-exposure to a new strain. CMV is frequently shed in the saliva and urine of young children for months after their own infection, making contact with toddlers a common source of exposure. The virus is transmitted through contact with these body fluids, not casual contact.
Washing hands thoroughly with soap and water for at least 15 to 20 seconds is highly effective, particularly after changing diapers or handling children’s toys. It is also advisable to avoid sharing eating utensils, cups, or food that has been in a young child’s mouth.