The 20-week ultrasound scan, sometimes called an anatomy or anomaly scan, is performed around 18 to 22 weeks of pregnancy. It checks the development of fetal organs and body parts and can detect certain congenital defects. In most cases, you can learn the sex of the fetus.
A 20-week ultrasound, sometimes called an anatomy scan or anomaly scan, is a prenatal ultrasound performed between 18 and 22 weeks of pregnancy. It checks on the physical development of the fetus and can detect certain congenital disorders as well as major anatomical abnormalities. Your healthcare provider will use a 2D, 3D or even 4D ultrasound to take images of the fetus inside your uterus. The ultrasound technician, or sonographer, will take measurements and make sure the fetus is growing appropriately for its age. You may also learn the sex of the fetus at this appointment.
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A 20-week ultrasound takes measurements of your fetal organs and body parts to make sure the fetus is growing appropriately. The scan also looks for signs of specific congenital disabilities or structural issues with certain organs.
Some specific parts your provider will examine are the fetal:
The ultrasound technician will also:
Several images are taken during this ultrasound. You will see the sonographer draw lines on the screen. This line acts as a ruler, documenting the sizes of organs and limbs. They compare these measurements against your due date. In some cases, you might hear you are measuring ahead, on track or behind your due date. If fetal measurements are within 10 to 14 days of the predicted due date, then the fetus is considered to be developing adequately. Your due date will not change unless the fetus measures outside of that time frame.
It may be hard for you to identify what you’re looking at on an ultrasound. You will most likely spot the fetus's head, nose, arms and legs. Unlike your first trimester ultrasound when the fetus looked like a tiny cluster of cells, the fetus looks more like a real baby at 20 weeks. Ask your ultrasound technician if you are unsure what you are looking at. Keep in mind, your technician can’t interpret the results of the scan for you. However, if you ask what body part you’re looking at, they can usually answer.
There isn’t much to do to prepare for your appointment. This will be one of your longer appointments — around 45 minutes for just the ultrasound. If you are seeing your healthcare provider afterward, your appointment could last up to 75 minutes. Plan ahead by making any necessary arrangements for work or childcare. Some healthcare providers recommend eating or having a full bladder to make it easier to see the images and make the fetus more likely to move.
First, you will lie down on the exam table. Next, an ultrasonic gel is placed on your belly. Then, an ultrasound technician will move an ultrasound wand over different spots in your abdomen. They will take images and measurements of specific organs and parts by freezing the screen. You may also see them draw lines to measure the length of the fetus's limbs or the circumference of its head. This helps them evaluate the fetus's size for its gestational age. You will get to watch the fetus on a screen, one of the most exciting parts of pregnancy.
If the fetus is positioned in a way that makes it hard to take measurements, the technician might ask you to move around a little or take a drink of something sweet to make the fetus move.
Generally, your ultrasound technician will be quiet as they work. Don’t be alarmed if the conversation is minimal or if they aren't sharing results as they go. Your obstetrician will go over the results with you either immediately after the ultrasound or at a follow-up appointment in the next few days.
After all the images are taken and your ultrasound technician is happy with all the angles and measurements, you will be able to wipe the gel off your belly.
Make sure there is room on your refrigerator: Most ultrasound technicians will send you home with a few pictures as a keepsake.
Yes, your fetus's external genitalia has developed enough to identify its sex. Depending on the position the fetus is in, your ultrasound technician may be able to see a penis or a labia. There is a slight chance that the fetus won't cooperate, and your ultrasound technician can’t get a clear picture of its genitals. If you don’t want to know the sex, speak up ahead of time so they don’t accidentally spoil the surprise. Most of the time, a prediction is made only when the technician is certain of sex.
No, having a 20-week ultrasound is safe. Studies have shown that ultrasound is not dangerous to you or the fetus. A 20-week prenatal ultrasound is considered medically necessary to detect potentially life-altering anomalies.
Anatomy scans are usually a positive experience. In most cases, your healthcare provider will not find any major anomalies. Every healthcare facility has different processes, but you will likely meet with your obstetrician right after your 20-week scan. The ultrasound technician shares the images and any findings with them. Then, your obstetrician will do their own analysis before meeting with you and sharing results.
If they find something that doesn’t look right, they may recommend additional prenatal testing or treatment for a condition found during the scan. In some cases, they recommend a wait-and-see approach. This means during delivery, they will watch for signs of the suspected condition and determine treatment at that time.
A 20-week ultrasound doesn’t find all congenital conditions. However, the scan can help detect several serious conditions:
It’s important to note that the scan results are not a formal diagnosis of any condition. Instead, it’s usually an indicator that further tests are needed. If your healthcare provider is concerned with any scans, they will speak to you about your next steps.
While the 20-week scan can detect certain conditions, it can’t identify everything. The scan is meant to provide indicators, or markers, of serious health problems. There are some conditions you will not know about until your baby is born. For example, many heart abnormalities are not found until birth and you might not know if your baby has scoliosis.
If your healthcare provider is concerned about anything in your 20-week scan, they may recommend further tests. Some of these tests could include amniocentesis, chorionic villus sampling or additional ultrasounds with a perinatologist (physicians who specialize in high-risk pregnancies).
Speak with your healthcare provider early in your pregnancy to make sure you understand the types of noninvasive prenatal testing available to you. Several tests that indicate an increased risk for congenital anomalies can be done before 20 weeks of pregnancy.
One of the best ways to identify a girl on ultrasound is to look for three lines. However, it’s always best to leave the identification of sex up to experienced professionals.
Sometimes it’s the absence of the three lines that tell the ultrasound technician you have a boy in your belly. Other times you can see a protrusion coming from a round sack. This is the fetus's penis and testicles. It’s always best to let your healthcare providers determine fetal sex.
A note from Cleveland Clinic
It’s normal to be both excited and nervous about your 20-week ultrasound appointment. You will get to see the fetus and find out how it's developing. Talk to your healthcare provider about any concerns you have so they can offer reassurance and ease your worries. In most cases, the 20-week anatomy scan is a positive experience for soon-to-be parents.
Last reviewed by a Cleveland Clinic medical professional on 04/01/2022.
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