Cytomegalovirus (CMV) in Pregnancy

Emily Oster

7 min Read Emily Oster

Emily Oster

Cytomegalovirus (CMV) in Pregnancy

How to think about the risk

Emily Oster

7 min Read

Cytomelagovirus, or CMV, is a common herpesvirus. In adults and healthy children, the virus is typically mild or asymptomatic. Like most herpesviruses, the pattern of infection is an initial “primary” infection, and then subsequent latent infection, which can cause flare-ups. (Think about genital herpes or cold sores).

CMV infection is extremely common. In parts of the developing world, virtually 100% of adults have been infected; in developed countries it may be more like 50%. Still, this is extremely common.

Because CMV doesn’t cause manifest disease in most adults and children, you may not have heard of it. However: CMV is among the most common causes of birth defects in the US, with a rate of around 1 in 1000 births. These birth defects range from mild to severe or fatal, with hearing loss (in one or both ears) being the most common. However even with this risk, pregnant women often do not hear about this until it may be too late. I’m disappointed to say that CMV is not featured in Expecting Better (although it will be the next time I revise).

This information needs to be out there. So let’s review: what is it, what are the concerns, how much risk is there, and what can you do about it?

CMV manifestations in pregnancy

The landscape of CMV in pregnancy is, frankly, confusing. The seriousness of the disease for the infant depends on the timing of maternal infection and transmission to the fetus. To help understand, I built a little visual, which I’m going to walk through in steps.

To begin: Infections with herpesvirus are classified in two ways. “Primary” infection is the first time someone is infected; “Non-Primary” are later flare-ups. During pregnancy, CMV infection in the mother can be either primary — this is their first exposure — or non-primary. In the US, an estimated 50 to 80% of prime-age adults have evidence of previous CMV infection. People in this group who got pregnant would have “Non-Primary Infection”. For pregnant people without previous exposure, the yearly risk of developing a primary infection is estimated at around 2.3%. For pregnant people, young children in a household are a significant exposure risk.

A flow chart for understanding CMV infections, primary vs. non-primary.

What this means is that most CMV infections in pregnancy are “non-primary”. The situation for pregnant people with a non-primary CMV infection is illustrated below. In most cases — 98 to 99% — non-primary infections are not transmitted to the fetus. In this case there is no CMV-related birth defect risk. However, in an estimated 0.15% to 2% of cases, there is transmission. Nearly all fetuses are asymptomatic in these cases, and generally do not show complications at birth. Unfortunately, an estimated 15 to 25% of these asymptomatic infections lead to later complications, most commonly hearing loss.

A flow chart for understanding CMV infections, non-primary, no fetal transmission vs. fetal transmission.

Primary CMV infection (infection among people who haven’t had it before) during pregnancy is much less common, but is more serious, as illustrated in the (more complicated) portion of the chart below. As with non-primary infection, if there is no transmission to the fetus, there is no CMV-related birth defect risk. However, transmission to the fetus during primary infection is much more common, and depends on the timing of infection during pregnancy.

Infection in the periconception period (4 weeks before to 6 weeks after the last menstrual period) is estimated to result in fetal transmission 21% of the time, for example. Transmission risk to the fetus is highest for infection in the third trimester.

Transmission to the fetus may then lead to asymptomatic infection — which would carry the same risks that it does when resulting from non-primary infection — or symptomatic infection, which is much more serious. Symptomatic infection most commonly results from infection early in pregnancy or right before.

Putting the transmission and symptomatic numbers together, primary CMV infection is most dangerous in the first trimester, where approximately 7% of CMV infections would lead to symptomatic illness in the fetus. Infection in the third trimester leads to symptomatic infection only about 0.2% of the time. The complications from symptomatic CMV infection in a fetus are variable and can be very serious. The mortality rate is estimated at 5%, and the risk of hearing loss is more than 50%.

A flow chart for understanding CMV infections, primary, no fetal transmission vs. fetal transmission with birth defect risks.

I put this all together in a single chart, to navigate not so much what to do (more on that below) but how to think about this.

A flow chart for understanding CMV infections, including primary, no fetal transmission vs. fetal transmission with birth defect risks, and non-primary, including transmission risks.

Can we lower CMV risk?

Given the serious and scary risks here, a natural question is: can they be lowered, and how?

The first best would be a vaccine, since CMV is a virus. When I talked with the Moderna CEO a few months ago, we talked briefly about their work to develop a CMV vaccine, which is currently underway. (You can learn more and get involved here).

For now, there is no vaccine, but there are possible approaches to lowering risk. The first thing to recognize is that you can only control or lower risk if you have never been infected with CMV before. If you are among the large share of the population who has had CMV, you are in the group with “non-primary” infection. On the one hand, this non-primary infection has relatively low risk. On the other hand, there is no risk mitigation to do.

How would you know if you were in this group? Testing. There are simple laboratory blood tests for CMV infection. These are not routinely ordered for pregnant people, which means both that there may be reluctance to order this testing and that insurance may not cover it. But you can ask.

There are good reasons why doctors may be reluctant to screen, largely reflecting the fact that there is not much to do, and either a positive or negative test can be scary. So this isn’t an obvious choice in either direction; it may depend on your own preferences.

If you haven’t been infected in the past, or you don’t know, there is a question of avoidance. For parents, small children are the most common vector of CMV; primary infection occurs about 25% of the time with a child shedding CMV, versus only 2% if they are not. Children can shed CMV virus for a long period of time after infection, and without a test (possible, very unlikely to be something you can access) it is hard to know if it is happening.

Enhanced hygiene behaviors (hand washing, avoiding intimate contact with urine or saliva) are suggested as ways to lower risks, with some limited evidence in favor of them. Of course, keeping up a long period of avoidance of your toddler is difficult.

Bottom line: risk reduction options here are limited. In my mind, there is a lot of value of getting a test. If you have a toddler and haven’t been exposed to CMV before, I think there is a strong argument for enhanced hand washing protocols and not sharing food with your baby or kissing them on the mouth. Yes, this is hard. It may also be worth it.

What if you are exposed?

Primary CMV infection during pregnancy appears, typically, as a flu-like illness. If you have such an illness, and if flu tests are negative, a CMV test is important. Pregnant people who have primary CMV infection should be carefully monitored for the possibility of complications with their infant. There are some newer treatment options, although nothing which has widespread agreement.

If this occurs, your doctor will be your best asset. An amniocentesis is common to test for fetal transmission, and frequent ultrasounds can detect physical abnormalities. Your baby will be more closely monitored both before and after birth.

Information and support

If you’d like to know more about this, try the National CMV Foundation. And if your pregnancy, baby or child has been affected by CMV, there are support groups.

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Just eat your Cheerios and move on.

Just eat your Cheerios and move on. ...

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According to the data we have, parents should sleep in the same room as a baby for as long as it works for them! Sharing a room with a child may have negative impacts on both child and adult sleep. We should give families more help in navigating these trade-offs and making the decisions that work best for them.

#emilyoster #parentdata #roomsharing #sids #parentingguide

The AAP’s guidelines recommend sleeping in the same room as your baby “ideally for the first six months.” However, the risk of SIDS is dramatically lower after four months, and the evidence in favor of the protective effect of room sharing is quite weak (both overall and even more so after four months). There is also growing evidence that infants who sleep in their own room by four months sleep better at four months, better at nine months, and even better at 30 months.

With this in mind, it’s worth asking why this recommendation continues at all — or at least why the AAP doesn’t push it back to four months. They say decreased arousals from sleep are linked to SIDS, which could mean that babies sleeping in their own room is risky. But this link is extremely indirect, and they do not show direct evidence to support it.

According to the data we have, parents should sleep in the same room as a baby for as long as it works for them! Sharing a room with a child may have negative impacts on both child and adult sleep. We should give families more help in navigating these trade-offs and making the decisions that work best for them.

#emilyoster #parentdata #roomsharing #sids #parentingguide
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Watch the full segment at the link in my bio 🔗

#tamronhall #tamronhallshow #emilyoster #parentingsupport #workingparents

It was an absolute pleasure to be featured on the @tamronhallshow! We talked about all things data-driven parenting and, in this clip, what I call the plague of secret parenting. To balance having a career and having a family, we can’t hide the fact that we’re parents. If mothers and fathers at the top can speak more openly about child-care obligations, it will help us all set a new precedent.

Watch the full segment at the link in my bio 🔗

#tamronhall #tamronhallshow #emilyoster #parentingsupport #workingparents
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Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#emilyoster #parentdata #parentdatapodcast #parentingpodcast #householdtips #fairplay #invisiblelabor

Invisible labor. It’s the work — in our households especially — that has to happen but that no one sees. It’s making the doctor’s appointment, ensuring birthday cards are purchased, remembering the milk.

My guest on this episode, @everodsky, has come up with a solution here, or at least a way for us to recognize the problem and make our own solutions. I’ve wanted to speak with Eve for ages, since I read her book Fair Play. We had a great conversation about the division of household labor, one I think you’ll get a lot out of!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#emilyoster #parentdata #parentdatapodcast #parentingpodcast #householdtips #fairplay #invisiblelabor
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Vitamins are just vitamins. Any prenatal vitamin that contains these is enough. 

Comment “Link” for a DM to an article with everything you need to know about prenatal vitamins.

#emilyoster #parentdata #prenatalvitamins #pregnancydiet #pregnancytips

Prenatal vitamins 💊 If there is any product that seems designed to prey on our fears, it’s this one. You’re newly pregnant and you want to do it right. Everyone agrees you need prenatal vitamins, so you get them. But do you want to be that person who just… buys the generic prenatal vitamins?

Good news: fancier vitamins are not better. Folic acid is the most important prenatal ingredient. Iron (with vitamin C) and DHA are also nice to have. Other included ingredients have only weak or no evidence to support their use. (If you do not consume animal products, add B12, plus a few others depending on your diet.)

Vitamins are just vitamins. Any prenatal vitamin that contains these is enough.

Comment “Link” for a DM to an article with everything you need to know about prenatal vitamins.

#emilyoster #parentdata #prenatalvitamins #pregnancydiet #pregnancytips
...

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#parentdata #emilyoster #newborncare #parentingadvice #parentingtips

When it comes to introducing your newborn to the world, timing matters. It’s a good idea to minimize germ exposure in the first 6-8 weeks; after that, it’s inevitable and, very likely, a good idea! This doesn’t mean you need to be trapped inside. The most significant exposure risks are from seeing other people at home — family, etc. These interactions are not infinitely risky, but they do pose more risk than a walk or a trip to the grocery store, since they involve closer interaction. Think simple and make sure everyone is washing their hands before holding the baby. 💛

#parentdata #emilyoster #newborncare #parentingadvice #parentingtips
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🔥 Hot Flash from ParentData is a weekly newsletter on navigating your health and hormones in the post-reproductive years. Written by Dr. Gillian Goddard, Hot Flash provides all of the information you need to have a productive, evidence-based conversation about hormonal health with your doctor.

#emilyoster #parentdata #hotflash #perimenopause #womenshealth

The first edition of Hot Flash is out now! Comment “Link” for a DM to learn more about the late-reproductive stage.

There are times when we expect hormonal shifts. Our reproductive lives are bookended by puberty and menopause. We discuss those changes often because they are definitive and dramatic — a first period is something many of us remember clearly. But between ages 13 and 53, our hormones are changing in more subtle ways. During the late-reproductive stage (in your 40s), you can expect a lot of changes in your menstrual cycle, including the length and symptoms you experience throughout. It’s an important time in our lives that is often overlooked!

🔥 Hot Flash from ParentData is a weekly newsletter on navigating your health and hormones in the post-reproductive years. Written by Dr. Gillian Goddard, Hot Flash provides all of the information you need to have a productive, evidence-based conversation about hormonal health with your doctor.

#emilyoster #parentdata #hotflash #perimenopause #womenshealth
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Now tell me in the comments: what’s a parenting move you’ve made recently that feels right to you?

#parentingcommunity #parentingsupport #parentingquotes #emilyoster #parentdata

There are plenty of reels telling you how to parent. Plenty of panic headlines saying that “studies show” what’s best for your kid. Even good data, from a trusted source, can send us into a spiral of comparison. But I want you to remember that no one knows your kid better than you. It’s important to absorb the research, but only you will know the approach that works best for you and your child. 💙

Now tell me in the comments: what’s a parenting move you’ve made recently that feels right to you?

#parentingcommunity #parentingsupport #parentingquotes #emilyoster #parentdata
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Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #parentdatapodcast #emilyoster #emilynagoski #comeasyouare #cometogether #longtermrelationship #intimacy #relationships

Let’s talk about sex (after) baby! Today on the podcast, I was lucky enough to speak with @enagoski about her new book on sexual connection in long-term relationships. Especially after having kids, this is something many people struggle with. Emily tells us to stop worrying about what’s “normal” and focus on pleasure in its many forms.

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #parentdatapodcast #emilyoster #emilynagoski #comeasyouare #cometogether #longtermrelationship #intimacy #relationships
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Comment “Link” for a DM to an article on another common formula question: should you throw away old formula powder?

#emilyoster #parentdata #babyformula #babyfeeding #parentingstruggles

Ever wondered if you can safely use leftover baby formula? 🍼 The CDC says to throw out unused formula immediately because of the risk of bacterial growth. However, research suggests that bacterial concentrations do not appreciably increase after 3, 12, or even 24 hours at refrigerator temperatures. Good news! This means there’s not a strong data-based reason to throw out formula right away if you store it in the fridge.

Comment “Link” for a DM to an article on another common formula question: should you throw away old formula powder?

#emilyoster #parentdata #babyformula #babyfeeding #parentingstruggles
...

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#emilyoster #parentdata #parentingtips #parentingadvice #newparents #parentingcommunity

What’s the most important piece of advice for new parents? Here’s one answer, but I want to hear from you! Share your suggestions in the comments ⬇️

#emilyoster #parentdata #parentingtips #parentingadvice #newparents #parentingcommunity
...

What's in the bag of a Vagina Economist? 👀 Someone please tell me this looks familiar to you.

What`s in the bag of a Vagina Economist? 👀 Someone please tell me this looks familiar to you. ...

Comment ”link” for a DM to learn more about tongue ties 🔗

Breastfeeding is often difficult, especially at the start. For babies with tongue ties, many infants (and their moms) struggle to get the hang of a good latch. This can lead to painful nipples and to inefficient feeding, and then low weight gain.

So what does the data say about the increasingly common practice of cutting tongue-ties in infants to improve breastfeeding success? Several weeks ago, @nytimes published a long and quite scary article on this topic.

After diving into the data, here is what I found. There is limited evidence that frenotomy procedures improve breastfeeding efficacy and the harms of the procedure are minimal. Many women do report that it alleviates pain and helps them with breastfeeding. However, it should not be a first-line treatment for breastfeeding problems.

#parentdata #emilyoster #tonguetie #tonguetiebabies #breastfeedingsupport

Comment ”link” for a DM to learn more about tongue ties 🔗

Breastfeeding is often difficult, especially at the start. For babies with tongue ties, many infants (and their moms) struggle to get the hang of a good latch. This can lead to painful nipples and to inefficient feeding, and then low weight gain.

So what does the data say about the increasingly common practice of cutting tongue-ties in infants to improve breastfeeding success? Several weeks ago, @nytimes published a long and quite scary article on this topic.

After diving into the data, here is what I found. There is limited evidence that frenotomy procedures improve breastfeeding efficacy and the harms of the procedure are minimal. Many women do report that it alleviates pain and helps them with breastfeeding. However, it should not be a first-line treatment for breastfeeding problems.

#parentdata #emilyoster #tonguetie #tonguetiebabies #breastfeedingsupport
...

Tag a friend who needs to hear this 💛 For many choices in parenting, there is no one right answer. We can use research and data to make informed decisions, but ultimately, it won’t tell you what to do. Only you can decide what will be best for your kids and your family.

I’m here to remind you to take a deep breath and trust yourself. I’ll be here to support you along the way. 

Thank you to everyone who submitted videos, including:
@sarah.consoli
@jess_lynn627
@nicolevandenwills
@thedrblair
@ncbenedict29
@haleycimini
@iamkellysnodgrass
@calesse_smith
@garnet__gordon
@jencoopgaiser87
@danigirl18c
@jamielundergreen
@carly_comber
@thecelebratingmama
@emilyannbynum
@eeliz413

#emilyoster #parentdata #parentingadvice #parentingsupport #parentingquotes

Tag a friend who needs to hear this 💛 For many choices in parenting, there is no one right answer. We can use research and data to make informed decisions, but ultimately, it won’t tell you what to do. Only you can decide what will be best for your kids and your family.

I’m here to remind you to take a deep breath and trust yourself. I’ll be here to support you along the way.

Thank you to everyone who submitted videos, including:
@sarah.consoli
@jess_lynn627
@nicolevandenwills
@thedrblair
@ncbenedict29
@haleycimini
@iamkellysnodgrass
@calesse_smith
@garnet__gordon
@jencoopgaiser87
@danigirl18c
@jamielundergreen
@carly_comber
@thecelebratingmama
@emilyannbynum
@eeliz413

#emilyoster #parentdata #parentingadvice #parentingsupport #parentingquotes
...