Neonatal cytomegalovirus (CMV) antibody IgG positivity is extremely common in clinical practice, and many parents mistake it for cytomegalovirus infection and become very worried, even leading to excessive medical attention. So, what exactly is a positive cytomegalovirus IgG in a newborn and can it cause damage to the child? Cytomegalovirus is a type of virus that is widely found in Chinese women of childbearing age. Once infected, cytomegalovirus is often present in the body for a long time or for life, but is often latently infected when the body is immune (i.e., no symptoms) and only shows obvious symptoms when the immune system is low. It has been reported in the literature that the positive rate of cytomegalic IgG in pregnant women in China is about 90-96.3%. In this group of people, most of them are latent infections and a few may have acute infections. Let’s understand what IgG antibodies are. It is one of the many antibody categories in the human body because it is relatively small and can easily pass through the placenta, so as long as a pregnant woman is cytomegalovirus IgG positive, the child she gives birth to will also generally be cytomegalovirus IgG positive. After understanding the above information, we can have a rational understanding of cytomegalovirus IgG positivity in newborns. Most newborns with positive cytomegalovirus IgG are born to mothers who have Ig antibodies in their bodies, and these antibodies reach the newborn through the placenta, which we call fetal antibodies, rather than the virus being passed to the child, which is the case with most newborns with cytomegalovirus antibodies. Of course there are a few newborns in which the cytomegalovirus is transmitted to the child through the placenta at the same time as the IgG antibodies. Cytomegalovirus infection of the fetus can produce different degrees of organ damage, including liver, hearing, brain, lungs, kidneys, etc. If the case is severe, antiviral treatment is required. So, the question arises, when faced with a positive IgG cytomegalovirus antibody in a newborn, how can one determine if it is simply a fetal transmission of antibodies or a true viral infection? In the absence of obvious clinical manifestations, a positive cytomegalovirus antibody IgG can be left untreated and the antibody titer will be rechecked 4-6 weeks after birth, if there is a significant decrease, then consider fetal transmission of antibodies; if the titer decrease is not obvious or even elevated, then cytomegalovirus infection should be considered and further improvement of related tests is needed.