Ultrasound is a type of medical imaging that uses sound waves. This creates an image of the inside of your body, without damaging anything. Many health care providers offer ultrasound scans at different moments in your pregnancy.
This article is pending medical review.
Contributors
Written by Patricia Posea, Diyora Rakhimova, Eva Muijtjens
Reviewed by Lea Dörner, Alessandra Papitto, Sophie Oppelt
Edited by Juliëtte Gossens
Ultrasound is an imaging technique that uses sound waves to create an image of the inside of your body. During pregnancy, it helps the doctor or midwife view the baby in your belly. An ultrasound is not harmful to the carrying parent or to the embryo or fetus. Throughout pregnancy, you will probably have ultrasound scans at different moments. Some of them are meant to assess if the embryo or fetus is growing properly and is the correct size for its gestational age (how many weeks pregnant you are). These are called fetal growth ultrasounds. Others, such as the 13 and 20 week ultrasounds, are done to screen for abnormal development of your baby’s body structures and to predict the date of delivery (1). In many countries, you can even ask for extra ultrasounds to check its sex or just to see your baby again!
This article will cover what the 13 and 20 week scans mean, their importance, the procedure, results, and next steps. We cover fetal growth ultrasounds in a different article.
Just a note: remember that every country is different! Not all ultrasounds mentioned here might be available where you live. You can ask your doctor or midwife what scans you could get.
What we're covering
What Are the 13 and 20 Week Scans?
Different kinds of tests can be performed during pregnancy to see how your baby is developing. While tests such as the NIPT detect chromosomal abnormalities, ultrasounds are performed to look for physical abnormalities in the fetus. This could be a heart defect, an abnormal number of fingers and toes (polydactyly), or an abnormality of the spine, for example.
A physical abnormality doesn’t necessarily mean there is also a chromosomal abnormality (which is a defect of somebody’s genetic information). This means that if a physical abnormality is found, your doctor might want to do further tests to verify what was found.
In short, the ultrasound is just a screening method and cannot diagnose a condition in your baby for sure. That is why further tests are needed for a correct diagnosis.
Initially, only the 20 week scan was part of the usual pregnancy screening tests, as this is considered an optimal time to see all the structures of the fetus (1). However, recent research shows that many (though not all) abnormalities can be identified through an ultrasound as early as 13 weeks (2–5). Since 2021, the 13 week scan started to be offered to pregnant people in the Netherlands, but only if they’re enrolled in the IMTAS study currently ongoing in the country (2). This study is aimed at measuring if such an early ultrasound brings parents peace of mind, or if it makes them more worried for the rest of the pregnancy.
In 2024, the government will decide whether the 13 week scan will be officially and permanently included in the existing pregnancy screening package in that country. Other countries offer similar ultrasound scans, including Australia.
At 13 weeks, though, your baby is still small - measuring around 7.5 cm (3 inches). It might be difficult to see some abnormalities at this stage. That’s why the 20 week scan is performed: your baby is bigger and more developed, measuring around 25.6 cm (10 inches). This makes it easier to spot abnormalities at this stage.
The 13-week scan - why and when?
In the Netherlands, you can have a 13 week scan from 12 weeks and 3 days up to and including 14 weeks and 3 days of the pregnancy. Other countries might use slightly different cut-offs, but the time frame will be similar. The scan can provide parents with information about abnormalities as early as possible. The earlier such abnormalities are identified, the more time parents have to make informed decisions about their next steps (1,3). That’s a plus! They could prepare themselves for the birth of a child with a bit more needs, for example, or consider an abortion, depending on the law in their country.
But there’s also a major downside: because the baby is still so small, it’s possible that an abnormality that was seen, isn’t actually anything to worry about. The baby could grow out of it, or it simply looked abnormal because of the small size of everything. Until further tests have confirmed it’s nothing bad, parents have been worrying about their baby’s health. This could add stress to the already uncertain time of pregnancy.
In addition, the ultrasound isn’t perfectly accurate. It’s possible that your baby has defects that aren’t detected on the 13 week scan. Or maybe it will still develop a defect that wasn’t there before. If you then do a 20 week ultrasound, they could see an abnormality that wasn’t seen before, while you thought that everything was okay. This could also be a reason not to do the 13 week scan.
The 20-week scan - why and when?
The 20 week scan is also called the ‘anatomy’ or ‘anomaly’ scan. In the Netherlands, you can have a 20 week scan from 18 weeks and 0 days up until 21 weeks and 0 days. Again, the time frame could be slightly different in other countries. Ideally, the scan should be performed in week 19. Just like the 13 week scan, this test can identify physical abnormalities. Since the pregnancy is already halfway through the second trimester, defects are more easily visible compared to the 13 week scan (1,3).
Both ultrasounds help the doctor or midwife identify a number of (rare) conditions, such as autosomal trisomies (check out our article here), heart, gut, or skeletal abnormalities. But an ultrasound doesn’t fully guarantee that such conditions will be identified if they’re present. Some abnormalities are easier to observe and identify than others. Both the 13 and 20 week ultrasounds provide some time for the parents and family to consider how to proceed with the pregnancy, after confirmation of the results through other tests. Some parents would like to terminate the pregnancy if the baby isn’t healthy. In the Netherlands, a pregnancy can be legally discontinued until 24 weeks. Doctors typically apply a limit of 22 weeks to observe a margin of error in the pregnancy duration. In extreme cases, abortion can be performed beyond the legal limit of 24 weeks. (6)
Check your local laws to see if abortion is a possibility in your case – but take care of yourself and be safe while getting this information. The website of the Center for Reproductive Rights could be helpful in this – check it out here.
The Procedure and What to Expect
How should you prepare for the 13-week scan?
First, parents should be counseled about the scan by a doctor or midwife. Counseling is an important part of any screening method or diagnostic test. It means that your healthcare provider will explain the scan to you and list the advantages and disadvantages. They should also have a conversation with you about why you would like to have the scan, and what you think you will do with the results. Helpful questions to think about are:
‘Do I really want to know if my baby has an abnormality?’
‘How will I feel about this?’
‘What do I see myself doing if I find out?’
Who will perform the scan and where depend on your country. It’s usually performed by a specially trained sonographer (ultrasound technician) or doctor. It might take place in a hospital or in a special clinic.
Make sure that on the day of the scan, you wear comfortable clothes that allow you to expose your belly. You can also bring a loved one, a friend, or a family member with you, for additional support.
Once inside the ultrasound room, you will be placed on your back. The sonographer will apply an ultrasound gel on your belly, which is needed to properly transmit the soundwaves used in an ultrasound scan. This can feel a little cold. Then, they will place the ultrasound probe on your belly, move the gel around, and start looking at your baby from head to toe. The whole procedure usually lasts around 30 minutes. The procedure is not dangerous and it doesn’t hurt you or your baby.
In some cases, the baby isn’t properly visible through your belly. Sometimes that’s the case if it’s in a certain position or there’s lots of bowel tissue in the way, for example. Your healthcare provider might offer to try an internal ultrasound instead. This is an ultrasound through your vagina instead of your belly. This doesn’t do any harm to you or the baby, either.
On the left, you can see a regular ultrasound probe. This is used on the abdomen. On the right, you can see a probe that is used for vaginal ultrasounds. © Freepik.
How should you prepare for the 20-week scan?
Just as for the 13 week scan, parents should carefully decide whether they want to have this examination or not. A doctor or midwife helps you with this as part of counseling. Who will perform the scan and where depend on your country. It’s usually performed by a specially trained sonographer (ultrasound technician) or doctor. It might take place in a hospital or in a special clinic.
Again, make sure to wear loose clothing so your belly can be easily exposed. The procedure will be the same as for the 13 week scan. Because your baby is so much bigger now, it’s unlikely that the scan needs to be done vaginally to see everything.
What does the sonographer look for?
The ultrasound is performed in the same way for both the 13 and the 20 week scans. The sonographer (person who performs the ultrasound) will assess your baby from head to toe. They will look at the skull, chest, abdomen, spine, arms, legs, and will see if all the vital organs (brain, heart, lungs, kidneys, bowels, bladder, genitals) look normal. The movements of the baby are evaluated and the heart function is always checked. The doctor will additionally assess the placenta and the fluid that surrounds your baby (amniotic fluid) (1).
At 20 weeks, the sonographer can also see your baby’s biological sex. You will decide whether you want to know it or not.
Results and Next Steps
After the sonographer finishes the examination, they will tell you the results and findings immediately. In 95% of cases, the results are normal. If everything seems good, no further steps need to be considered. However, the sonographer will always mention that even if the ultrasound seems normal, there is no 100% guarantee that the baby has no abnormalities. This could be the case when some parts can’t be evaluated properly, either due to the position of the baby, or just unclear views on the ultrasound. If this happens at the 13 week scan, the sonographer will reassess these parts again at the 20 week scan. If this is the case at 20 weeks ultrasound, then the ultrasound is repeated a few days to a week later, and you might be offered another structural scan in the third trimester (1,3). Additionally, not all abnormalities are visible on ultrasound to begin with.
When the sonographer finds something suspicious, you might be offered further testing and a more focused ultrasound. Usually, blood tests are performed, but in some cases, doctors might offer more invasive prenatal tests, such as an amniocentesis. If you want to know more about invasive prenatal testing, check out this article.
Advantages and Disadvantages
We’ve already touched on some of the advantages and disadvantages above, but we’ll summarize them here as well.
One of the advantages of the 13 and 20 week ultrasounds is that you, when the test results are normal, feel more assured that everything seems to be going well (7). If the test result shows defects, you can decide how to proceed with the pregnancy, and you can prepare yourself for what’s to come. You can learn about your baby’s needs for when they are born, so that specific care can be given straight after delivery.
A disadvantage is additional stress, either from waiting for the result or anticipating the ultrasound. Moreover, if the ultrasound shows abnormalities, the birthing parent can experience a lot of emotional stress, which can affect the pregnancy negatively (8,9). It needs to be kept in mind that an abnormality in the ultrasound doesn’t automatically mean that the baby is unhealthy. Nonetheless, this can still cause a lot of distress.
It’s also important to realize that the ultrasound examinations can’t give definite results about the health of your baby. They can only make it more or less likely that everything is okay.
There aren't any right or wrong choices when deciding about these ultrasounds. Make the choice that feels right to you!
References
Shipp TD. Overview of ultrasound examination in obstetrics and gynecology. In: Simpson LL, Levine D, Barss VA (eds.). UpToDate. 2023.
Meer over de Imitas Studie: Onderzoek Naar de 13 wekenecho. https://13wekenecho.org/ik-ben-zorgverlener/over-de-imitas-studie/.
Rijksinstituut voor Volksgezondheid en Milieu. Brochure the 13-week scan and the 20-week scan. 2021. https://www.pns.nl/documenten/the_13-week_scan_and_the_20-week_scan.
Kenkhuis MJ, Bakker M. Effectiveness of 12-13-week scan for early diagnosis of fetal congenital anomalies in the cell-free DNA era. Ultrasound in Obstetrics & Gynecology. 2018;51(4):463–469. DOI:10.1002/uog.17487.
International Society of Ultrasound in Obstetrics and Gynecology, Bilardo CM, Chaoui R, Hyett JA, Kagan KO, Karim JN et al. ISUOG Practice Guidelines (updated): performance of 11–14-week ultrasound scan. Ultrasound in Obstetrics & Gynecology. 2023;61(1):127-143. DOI: 10.1002/uog.26106.
Ministerie van Algemene Zaken. What is the time limit for having an abortion? https://www.government.nl/topics/abortion/question-and-answer/what-is-the-time-limit-for-having-an-abortion.
Bardi F, Bakker M. Psychological outcomes, knowledge and preferences of pregnant women on first-trimester screening for fetal structural abnormalities: A prospective cohort study. PLOS ONE. 2021;16(1). DOI:10.1371/journal.pone.0245938.
Traylor CS, Johnson JD, Kimmel MC, Manuck TA. Effects of psychological stress on adverse pregnancy outcomes and nonpharmacologic approaches for reduction: an expert review. American Journal of Obstetrics & Gynecology MFM. 2020;2(4). DOI: 10.1016/j.ajogmf.2020.100229.
Coussons-Read ME. Effects of prenatal stress on pregnancy and human development: mechanisms and pathways. Obstetric Medicine. 2013;6(2):52-57. DOI: 10.1177/1753495X12473751.
Please note: the information we provide to you here is for educational purposes only. If you’re experiencing any discomfort or have any complaints or questions about your health, please contact your doctor or other relevant health professional. We don’t provide medical advice.
PREhealth is not affiliated with the Center for Reproductive Rights.
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