Can I pass CMV to my baby if I had it before pregnancy?

Yes, it is possible to pass cytomegalovirus (CMV) to your baby even if you were infected before you became pregnant, though the risk is much lower. If you had CMV in the past, your body made antibodies (immune system proteins) to fight it. These antibodies provide significant protection for your baby during pregnancy. However, because CMV remains dormant (inactive) in your body for life, the virus can sometimes wake back up, or you can catch a different strain ^[1][2]. If the virus becomes active again and passes to your baby, it is called a non-primary infection.

A past positive antibody test by itself does not mean you currently have an active infection that is threatening your baby. Most pregnancies in people with prior CMV immunity do not result in a baby with serious CMV-related problems.

Primary vs. Non-Primary Infection

To understand your risk, it helps to distinguish between a first-time infection and an infection that happens when you already have immunity:

• Primary Infection: This means you caught CMV for the very first time while pregnant. Because your body has not built up immunity yet, the virus has a higher chance of crossing the placenta (the organ that provides nutrients to your baby). The risk of passing the virus to your baby after a primary infection is estimated to be between 30% and 50% ^[3].
• Non-Primary Infection: This occurs when you already had immunity before pregnancy, but the virus becomes active during pregnancy. This can happen through reactivation (the dormant virus wakes up) or reinfection (you catch a new strain of CMV) ^[1][2]. Because you already have antibodies, the chance of the virus reaching your baby is significantly lower, with the overall population risk often estimated around 1% ^[3].

What This Means for Your Baby

While your prior immunity greatly lowers the chance of your baby getting infected (known as congenital CMV), it does not eliminate the risk entirely ^[3][4].

Most infants born with congenital CMV have no symptoms at birth. However, if the virus is passed to your baby, serious complications can still occur. Research shows that babies infected due to a non-primary maternal infection can still develop hearing loss, brain abnormalities, or developmental delays ^[5][6][7]. In fact, among the small percentage of babies who do get infected, the severity of long-term hearing and developmental problems is not necessarily lower just because the mother had prior immunity ^[4][6].

Certain factors, such as medical conditions or treatments that weaken your immune system (immunosuppression), might increase the risk of the virus reactivating and being passed to your baby ^[2][8]. Examples include treatments for autoimmune diseases, organ transplants, or HIV. Never stop taking prescribed medications without discussing it with your doctor first.

Testing and Next Steps

If you are concerned about your CMV status, your doctor may look at specific blood tests ^[9][10]:

• IgG Test: A positive result usually means you had a past infection.
• IgM Test: This can show a recent infection, but it can also stay positive for a long time or be a false positive, so it doesn’t prove a new infection by itself.
• IgG Avidity: This helps doctors determine how recently a primary infection occurred.

If there is a concern that your baby might be infected, your doctor might recommend an ultrasound. However, a normal ultrasound does not rule out infection or later hearing loss. If more information is needed, your doctor may discuss amniocentesis, a procedure where a small amount of amniotic fluid is tested for the virus. This is generally considered after 21 weeks of pregnancy and at least 6 weeks after the suspected maternal infection. Finally, if congenital CMV is suspected after birth, your baby’s saliva or urine must be tested within the first 21 days of life to confirm.

Protecting Yourself

Even with prior immunity, it is still a good idea to practice good hygiene to lower your chances of catching a new strain of CMV:

• Wash your hands thoroughly with soap and water, especially after changing diapers or touching a child’s saliva or nasal secretions.
• Do not share food, drinks, utensils, toothbrushes, or pacifiers with young children.
• Avoid kissing young children directly on the mouth or cheek (kiss them on the forehead or top of the head instead).

You do not need to isolate yourself from children, but these steps can help reduce your exposure.