20 Week Ultrasound: What Exactly Happens During This Scan

Everything you need to know about getting a 20 week ultrasound. Plus, what exactly are sonographers looking for during the scan? Find out here!

Everything you need to know about getting a 20 week ultrasound. Plus, what exactly are sonographers looking for during the scan? Find out here!

The 20-week milestone is a big one! Leaving those early pregnancy signs in the dust, you’re at the halfway point of your pregnancy. ? This is also the time when many women get a 20 week ultrasound.

In this article, we’ll explain everything you need to know about the 20 week ultrasound, including:

  • What healthcare providers look at during the 20 week ultrasound
  • What to expect at your 20 week ultrasound
  • The pros and cons of having a 20 week ultrasound
  • Plus, how to minimize the effects of an ultrasound

What is the 20 Week Ultrasound?

The 20 week ultrasound, also known as the anatomy scan, is when a sonographer uses an ultrasound machine to:

  • Check for physical abnormalities in baby
  • Check mama’s uterus, fluid levels, and placenta
  • Determine baby’s sex

Though it’s referred to as the 20 week ultrasound, most women have the exam some time between 18 and 21 weeks. 

20 Week Ultrasound: How to Prepare

The preparation is minimal for the scan, but here are a few do’s and don’t’s:


  • Wear lose, comfortable clothing. Elastic pants or a flowing dress are great options since you can easily access belly for the scan.
  • Get childcare for older siblings. Many radiology centers do not allow children to accompany mamas to the appointment.


  • Empty your bladder. To ensure the inside of the abdominal area is clearly seen on the ultrasound images, you should have ample fluid in your bladder. Many practitioners will ask you to drink at least 16 ounces, one hour before test.

Pregnant? Get my FREE week-by-week updates! – Week by Week Promo [In-article]

Track your baby’s growth, find safe and natural remedies, and have fun along the way!

Get Pregnancy Updates!

20 Week Ultrasound: What Happens

Here’s what you can expect at your 20 week ultrasound:

  1. You will be asked to remove clothing so the sonographer can easily access your bare belly.
  2. You will then lay semi-reclined on an exam table with belly exposed from the lower ribs to the top of the hips.
  3. The sonographer will spread a clear gel on your belly.
  4. Next, the sonographer will move a probe called a transducer all over your abdomen. This transmits sound waves that go through the abdominal wall. These waves bounce off of the organs and bones of your developing baby to produce images on the monitor.
  5. During this process, the sonographer looks at a screen that shows the image of the baby, records measurements, and takes pictures. Oftentimes, this screen is also visible to you and others who are present at the ultrasound.
  6. There is a lot of information to gather during the 20 week ultrasound. Expect to be there anywhere from 30 minutes to an hour, depending on how wiggly your baby is and how fast your sonographer is.
  7. If the sonographer is tight-lipped throughout the process, don’t fret. Sonographers need to focus on getting the information they need. They’re also not legally supposed to share information with you. That being said, most sonographers will point out some obvious things he/she is seeing, like the beating heart and spine, and baby’s sex (if you are interested to find out if you’re having a boy or girl)!
  8. Once the sonographer has finished the ultrasound, they will most likely snap some pictures of your baby for your records—and for you to take home, if you wish.
  9. Once the ultrasound is complete, a radiologist will review your results, then forward them to your healthcare provider, who will share the results with you.

(Note: It’s always a good idea to ask your healthcare provider if there are any special procedures that you should follow.)

20 Week Ultrasound: What are Health Providers Looking For?

So now you know what to expect, but what exactly are they looking for? A 20-week ultrasound provides a fairly comprehensive look at what’s going on in your uterus!

Here’s the full scope:

    • Heartbeat: The sonographer will look for a heartbeat that has a nice variability, taking note of its rhythm. According to studies, fluctuations of beat-to-beat intervals is considered the most important fetal heart rate indicator of baby’s development. In a relaxed state, the variation between heart beats is high. In a stressed state, the variation is low. A high heartbeat variation shows resilience and correlates with overall health. (source)
    • Amniotic fluid: The sonographer will measure the pockets of fluid that surrounds the baby to make sure there is an average amount of fluid– not too little, not too much, an indirect sign of fetal health.
    • Baby’s position: Next, they take a look at how the baby is positioned in the uterus—head up or head down! (Note: At this point in the pregnancy, a baby has tons of room—so don’t fret if baby is breech, there is plenty of time for baby to get into an optimal position.) 
  • Anatomy measurements: The sonographer takes different measurements, like head circumference, femur length, and the abdominal circumference. These measurements help the sonographer:
    • Give your baby a percentile for size.
    • See if baby’s size correlates with the due date. Occasionally, if the baby is larger or smaller than expected, your due date may be changed.
  • Anatomy development: After the measurements, the sonographer conduct’s a head-to-toe exam on baby, looking at the spine, brain, heart, lungs, diaphragm, stomach, intestines, kidneys, and bladder for any abnormalities. They even count the fingers and toes!
  • Baby’s sex: If you so choose, the sonographer can reveal baby’s sex!
  • Placenta: The next part of the scan involves locating the placenta to determine it’s position and check for a condition called placenta previa. He/she will also examine overall placenta health and vascularity.
  • Umbilical cord: Then, the sonographer looks at the umbilical cord to see where it attaches to the placenta (and the baby!). He/she also notes blood flow in the placenta and the cord.
  • Maternal structures: Lastly, the sonographer will take a peek at some of the other maternal structures like:
    • The uterus to check for fibroids.
    • The ovaries to check for cysts or masses.
    • And the cervix to measure length and position.

What Do They Screen For During the 20 Week Ultrasound?

Through the above process, this detailed scan allows the sonographer to look specifically for indications of 11 rare, but serious conditions, including:

While this scan can give you quite a bit of information about your baby’s well-being, it is important to remember that baby is still developing. Please know that a positive 20 week ultrasound is a great milestone—and one that should be celebrated—but it can’t pick up everything.

Is a 20 Week Ultrasound Necessary?

One might get ‘mandatory’ and ‘routine’ confused when it comes to prenatal testing. Though the 20 week ultrasound is routine, it is not necessarily mandatory.

Not every woman wants or even needs a 20 week ultrasound.

In fact, studies do not show improved baby or maternal outcome in those who opt to have a mid-pregnancy ultrasound.

That said, many mamas and papas prefer to have a 20 week ultrasound to bond with the baby and get peace of mind.

What if the 20 Week Ultrasound Indicates a Problem?

Identifying a problem during the 20 week ultrasound may or may not be a good argument for having the scan to begin with. You’ll have plenty of time to understand the condition and set up the appropriate medical team for after-birth care.

Keep in mind, though, some conditions uncovered during a 20 week ultrasound resolve themselves with time, such as:

  • Water on the kidneys. Sometimes a scan will show water on the kidneys, which most often clears up on its own as baby continues to grow and develop.
  • Placenta previa. Another common scenario is when a scan identifies placenta previa. According to studies, 98 percent of marginal placenta previas are resolved at a mean gestational age of 28.6 weeks.

Once an ultrasound indicates a problem, your healthcare provider may suggest further scans and follow-up to tests to track progress and gather more information.

Is the 20 Week Ultrasound Dangerous?

Though ultrasounds are regarded as safe to mama and her baby, experts say, like any medical procedure, it does carry some inherent risk—namely the potential for misdiagnosis and the fact that ultrasound does impact the body. Current research is not strong enough to prove ultrasound harms mama or her baby, but because it’s a form of energy that heats tissue, it may have an effect on the biological tissues it traverses. (source)

Bottom line: Many women have ultrasounds every day, with no known effects. Still, more research is needed.

Just remember: It’s recommended that ultrasound exams be performed only for medical reasons by qualified health care professionals.

When Are Ultrasounds Necessary?

As natural mamas, we try to avoid as many interventions as possible. But sometimes it’s in your best interest to have an ultrasound. Here are few of those scenarios:

  • Monitoring twins or higher order multiples
  • Understanding why you’re measuring large/small
  • Identifying the reason for vaginal bleeding in pregnancy
  • Confirming position of placenta if placenta previa was an issue

How to Minimize the Effects of Ultrasounds

Because there is still much to learn about the safety of ultrasounds, consider these strategies to reduce the effects of ultrasound:

  • Stick with a more traditional 2D ultrasound. Skip the 3D or 4D. This fad of having a more lifelike picture of your baby in the womb is on the rise, despite warnings from the Food and Drug Administration (FDA) and the American Congress of Obstetricians and Gynecologist (ACOG).
  • See if you can wait until 22 or 23 weeks. This gives your baby a little more time to develop and the placenta a chance to move. Sometimes, when you opt for having the scan on the earlier side, doctors or midwives may need to do a repeat scan in just a few weeks to better assess the baby’s development.
  • Ask to forgo the doppler and use a fetoscope instead. At around 20 weeks, you can listen to baby’s heartbeat via a fetoscope instead of a hand-held doppler. Studies show that a handheld doppler emits waves at a higher temperature. Though there is no conclusive evidence, as stated above, this could potentially affect the tissue it transverses.  
  • Forgo pictures. A sonographer may spend extra time getting a perfect profile pic, and extra time means the potential for extra exposure.
  • Be upfront with the sonographer. It’s ok to let the sonographer know that you are concerned about the effects of ultrasound. Ask for the scan to be complete, but efficient.

How About You?

Did you have a 20 week ultrasound? Is there anything you wish you knew beforehand?

Genevieve Howland

About the Author

Genevieve Howland is a doula and childbirth educator. She is the bestselling author of The Mama Natural Week-by-Week Guide to Pregnancy and Childbirth and creator of the Mama Natural Birth Course. A mother of three, graduate of the University of Colorado, and YouTuber with over 135,000,000 views, she helps mothers and moms-to-be lead healthier and more natural lives.


  1. I just had the anatomy scan done and my doctor called me after, saying they want me to come back for another ultrasound in 2 weeks . She told me it was because they hadn’t had a clear picture of the babys head. Is this normal? Should i be worried?

    • I think that’s fine. I had my US yesterday, and she said if the baby isn’t in the right position for viewing all they need to view, they may ask me to come back.

  2. We never had an anatomy scan with our first four, but did for our fifth. It was a good thing in a way because we found out he had CPAM. In worse situations, the baby needs surgery while in the womb. We were blessed that his was not as bad and could wait until he was six months old. We could have lost him if his CPAM was worse and we did not know about it. At time of his surgery, the said the lung tissue was already inflamed. Our third child we just found out at almost 7 years old she has a minor heart condition. It is nice that we did not have to worry all these years for a minor condition, so I guess we can see it both ways for anatomy scans.

  3. For my first pregnancy I didn’t do any research about ultrasounds beforehand, so when the doctor saw fluid in my son’s kidneys and made it sound like it was a serious complication, we let her talk us into having a second ultrasound to check up on it, and then a third when it still hadn’t resolved. We ended up following up on it after he was born, and there was a lot of fear-mongering by doctors who wanted to do invasive procedures to “check whether he’s at risk of getting a bladder infection”, and even chided us for not circumsizing him because that would make him more susceptible to UTIs which could then spread to his bladder. In the end, we skipped all the invasive procedures and the issue resolved itself within a few months. I feel like we could have saved ourselves a ton of grief and stress if we’d known it was a common issue and not done all the follow up ultrasounds. Also, I let them talk me into getting 3D scans and pictures, because I had never heard of them and didn’t realize there was any risk associated. I was pretty mad when I found out, and wished I’d done more research beforehand. But there’s SO much to learn when you’re becoming a first time parent, and even the most informed of us often don’t know how much we don’t know.

    For my second pregnancy, I was more careful, and limited it to the one 20-week ultrasound, but still ended up spending way more time on the table than I wanted, because the technician kept insisting she was having trouble getting the baby into the right position for some of the pictures she needed to take. Finally I asked what she still needed, and it turned out she’d spent the last 10 minutes trying to rule out a cleft lip and a club foot (my daughter had neither). Which seemed ridiculous because I wasn’t about to do anything differently due to minor non-life-threatening birth defects that could be easily fixed with surgery after the birth.

    Third time, I’m doing my one ultrasound with an ob who’s more comfortable with my style of low-intervention pregnancy and birth (he even contratulated me on my 2 previous home births). I’m also being more vocal about my preferences, like my desire to limit my baby’s ultrasound exposure, and my priorities in terms of what kind of information I care about and what measurements I can live without if they’re not easy to get.

    • I also want to do a quick ultrasound and not have to check every single part of my baby. I just don’t think it’s nessesary. What are the basic things I should ask to check at my baby’s anatomy ultrasound?

  4. I’m trying to decide if doing the anatomy scan is wise and loving for my baby and I think my biggest question is: in cases of a rare prenatal diagnosis, would it make a significant difference to know in advance (to switch from home birth to hospital)? Also, I’m only reconsidering now at about 26 weeks, so is it too late either way? Thanks!

    • I’m not sure how old this comment is, but I’m replying for the sake of anyone else reading. Significant issues were found with my daughter due to our anatomy scan. Instead of a home birth, for which I had seemed like an ideal candidate, I will be delivering two hours away at a hospital. We have a lot to prepare differently, due to her diagnosis. It may not be so common, but you never know when something like this will happen to your own child.

      • Thankfully significant issues with any baby are rare. But I wonder if all the “issues” you were told about with your child actually were accurate once your child was born.

        We know statistically negative diagnosis in pregnancy have an unbelievably high rate of false positives. Leading parents to worry and stress needlessly.

  5. The Placenta Previa study mentioned only studies cases of placenta previa that resolved. The NIH study used a sample of only women who’s placenta previa resolved, so 100% of them resolved. It doesn’t represent the percentage of cases of placenta previa that actually resolve, as this article claims. You need to read the study – it’s not correctly represented here.

    • Actually Patrick, your comment does not reflect the study accurately.

      Here is a direct copy and paste from the NIH study:

      “Of the 366 cases, 84% of complete placenta previas and 98% of marginal placenta previas resolved at a mean gestational age of 28.6 ±5.3 weeks.”

      Not ALL placenta previa cases resolved in the study, as you erroneously claim.

  6. The anatomy ultrasound was the only one I had. I was planning a home birth and felt that it was important to ensure there were no serious risk factors present so that I could switch my birth to the hospital, if needed. Luckily all was well! I have a brother with Down’s Syndrome (trisomy 21), though, and I told my sonographer. Ultrasound cannot confirm Down’s, but it can look for possible indicators. After I told her that I think she measured the nuchal fold about 5 times!

Add Comment

Your email address will not be published. All fields are required *


Learn to have an amazing birth

(without leaving your couch)

Baby Name Finder

Discover thousands of unique and popular baby names with Mama Natural’s NEW Baby Name Finder.