The Leading Cause of Birth Defects You've Likely Never Heard of

If you’re pregnant, trying to conceive, or potentially want to have children someday, understanding the risks associated with cytomegalovirus — and learning how to protect your baby — is super important.

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For expecting parents, the nine months spent waiting for a baby to arrive are packed with planning. Whether it's painting the nursery, sifting through cute onesies, or even packing a hospital bag, for the most part, it's a pretty exciting, joy-filled time.

Of course, bringing a child into the world can also be a particularly stressful experience, namely when it comes to the baby's health. And while many ailments can be spotted via ultrasound or addressed shortly after birth, other serious issues show no symptoms or warning signs — or are virtually unknown by the general public (and seldom discussed by doctors).

One prime example is cytomegalovirus (CMV), a virus occurring in one out of every 200 births that can result in a host of harmful birth defects. (

"CMV has a significant awareness problem," explains Kristen Hutchinson Spytek, president and co-founder of the National CMV Foundation. She notes that only about 9 percent of women (yes, just nine) have even heard of CMV, and yet, "it's the most common infectious cause of birth defects in the United States." (That includes genetic disorders like down syndrome and cystic fibrosis, as well as viruses like Zika, listeriosis, and toxoplasmosis, she adds.)

CMV is a herpes virus that, while able to affect folks of all ages, is typically harmless and symptomless for adults and children who aren't immunocompromised, says Spytek. "Just over half of all adults have been infected with CMV before the age of 40," she says. "Once CMV is in a person's body, it can stay there for life." (

But here's where it gets problematic: If a pregnant person carrying a baby is infected with CMV, even if they don't know it, they can potentially pass the virus onto their unborn child.

And passing CMV to an unborn child can wreak serious havoc on their development. According to the National CMV Foundation, of all kids born with a congenital CMV infection, 1 in 5 develop disabilities like vision loss, hearing loss, and other medical issues. They'll often struggle with these ailments for their entire lives, as there's currently no vaccine or standard treatment for CMV (yet).

"These diagnoses are devastating for families, affecting more than 6,000 babies [in the United States] per year," says Spytek.

Here's everything you need to know about CMV, including how it's transmitted and what you can do to keep yourself (and and potentially a new baby) safe.

Why CMV Is One of the Least Discussed Devastating Diseases

While the National CMV Foundation and other organizations are working overtime to educate the public on CMV's ubiquitous (and dangerous) nature, the way the virus is transmitted can make it a taboo subject for doctors to discuss with expecting parents or people of child-bearing age, says Pablo J. Sanchez, M.D., pediatric infectious diseases specialist and principal investigator in the Center for Perinatal Research at The Research Institute.

"CMV is transmitted through all bodily fluids, such as breast milk, urine, and saliva, but it's most prominent through saliva," explains Dr. Sanchez. In fact, CMV was originally called the salivary gland virus, and is most common in children ages 1 through 5 — and especially in day care facilities. (

What this means: If you're a pregnant person and either have another child, or care for young children, you're particularly at risk for passing it onto your baby.

"As we know, young children tend to put just about everything in their mouth," Dr. Sanchez says. "So if a [pregnant person] is caring for a young child infected with the virus, sharing cups and spoons or changing diapers, [they] could potentially become infected."

It's important to note that this transfer wouldn't exactly cause harm to the adult (unless they're immunocompromised). Again, the danger lies in passing it to the newborn.

Of course, as anyone who's cared for a small child knows, there is a lot of spit and snot involved. And while continuous hand- and dish-washing isn't always the most convenient prevention strategy for stressed-out caretakers, according to Spytek, the benefits far outweigh the inconveniences — something the medical community isn't always quick to point out.

"Medical practitioners have very limited knowledge about CMV, and they often downplay its risks. There isn't a standard of care among medical associations for counseling pregnant people," she explains, noting that the American College of Obstetricians and Gynecologists suggests that counseling and suggesting intervention strategies for pregnant people with toddlers at home is "impractical or burdensome." One survey found that fewer than 50 percent of ob-gyns tell pregnant people how to avoid CMV.

"[Their] justifications just don't hold up," reiterates Spytek. "And the truth is, there is incredible guilt, fear, and sadness associated with each CMV-related outcome or resulting diagnosis for the parents — this reality is what's burdensome."

Plus, as Dr. Sanchez points out, CMV isn't linked to any particularly risky behaviors or specific risk factors — it's just something humans carry. "That's what mothers always tell me — that everyone told them to stay away from cats [which can carry diseases dangerous for expecting parents], not from their own children," he notes.

Another major setback with CMV, according to Dr. Sanchez? There's no treatment or cure. "We need a vaccine," he says. "It's been the number-one priority to develop one. There's been ongoing work, but we're not quite there yet."

What Does CMV Look Like In a Baby Infected in the Womb?

CMV can manifest itself in different ways (and for some, there are no symptoms at all). But for those babies who do exhibit symptoms, they're serious, says Dr. Sanchez.

"Of those [babies] who show signs of infection, some can be severe," he explains. "That's because when the virus crosses the placenta and infects the fetus early in gestation, it can move to the central nervous system and now allow brain cells to migrate to normal places. This results in neurological issues because the brain isn't formed well."

According to the National CMV Foundation, if you have CMV during pregnancy, there's a 33 percent chance you'll pass it to your baby. And of those infants who are infected, 90 percent of babies born with CMV don't show symptoms at birth, while the remaining 10 percent show some sort of physical abnormalities. (So if you're pregnant, again, it's important to limit your exposure to small children who could potentially be carrying the virus.) (

Beyond brain disorders, Dr. Sanchez notes that hearing loss is a particularly common symptom associated with CMV, oftentimes appearing later in childhood. "With my adolescent patients, if the hearing loss is unexplained, I usually know [they were infected] with CMV while in the womb."

And while there's no vaccine or cure-all treatment for CMV, screenings are available for newborns, and the National CMV Foundation is currently working on recommendations. "We believe universal newborn screening is an important first step in driving awareness and behavioral change, hopefully mitigating the risk of serious outcomes due to congenital CMV," Spytek explains.

Dr. Sanchez notes that the screening window is short, so it's important to prioritize testing immediately after birth. "We have three weeks where we can diagnose congenital CMV and see if long-term risks can be identified."

If CMV is diagnosed within that three-week period, Spytek says that certain antiviral medications can often reduce the severity of hearing loss or improve developmental outcomes. "The damage previously caused by congenital CMV cannot be reversed, however," she explains. (

While there are screenings for adults, Dr. Sanchez doesn't recommend them to his patients. "Many people in the [CMV community] feel strongly that [pregnant people] should be tested, but not me. Whether they're CMV-positive or not, they need to take precautions."

How to Prevent CMV If You're Pregnant

While there's no current treatment or vaccine for CMV, there are a handful of preventive measures people who are pregnant can take to prevent contracting and transferring the disease to an unborn child.

Here are Spytek's top tips from the National CMV Foundation:

  1. Don't share food, utensils, drinks, straws, or toothbrushes. This goes for anyone, but especially with children between the ages of one and five.
  2. Never put a pacifier from another child in your mouth. Seriously, just don't.
  3. Kiss a child on the cheek or head, rather than their mouth. Bonus: Babies' heads smell ah-mazing. It's a scientific truth. And feel free to give all the hugs!
  4. Wash your hands with soap and water for 15 to 20 seconds after changing diapers, feeding a young child, handling toys, and wiping a young child's drool, nose, or tears.
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