What is an anatomy scan in pregnancy?
What is an anatomy scan in pregnancy?
It is the standard ultrasound exam in the middle of pregnancy, including a survey of the baby's anatomy. ACOG says you should have at least one standard exam during pregnancy, usually at 18 to 22 weeks, and that it checks the fetus's physical development, screens for major congenital anomalies and estimates gestational age. A handheld transducer sends sound waves through the body, and the echoes are turned into pictures on a screen. ACOG's practice bulletin, written with the American Institute of Ultrasound in Medicine (AIUM), calls obstetric ultrasound an important and common part of obstetric care in the United States. The practice parameter AIUM shares with ACOG and other societies lists the anatomic survey as one part of the second-trimester exam, alongside the baby's position, fluid, placenta and growth.
This is not clinical evidence and not medical advice. It does not replace your care team. Discuss anything here with your clinician before you act on it.
Arun Verma, co-founder of Triangle · Published · Updated
The mid-pregnancy scan report is full of measurements and terms, and it may come from an ultrasound clinic rather than the practice you see for visits.
When is the anatomy scan done, and why not earlier?
Usually at 18 to 22 weeks. The practice parameter says fetal anatomy may be adequately assessed after approximately 18 weeks, and that before then some structures can be hard to see because of the baby's size, position or movement. An earlier scan has a different job. ACOG says a first-trimester exam is not standard because it is too early to see many of the fetus's limbs and organs in detail, and that an early scan is used to estimate gestational age, count fetuses and check the heart rate, among other uses. Cervix length is a separate mid-pregnancy measurement, not an earlier substitute for the anatomy scan. MedlinePlus says many women also have their cervix length measured by vaginal ultrasound around 20 to 24 weeks. An August 2026 study in Obstetrics & Gynecology compared an expanded standardized first-trimester fetal anatomic ultrasound protocol at 11 6/7 to 13 6/7 weeks with ISUOG first-trimester protocols for how many structural anomalies were detected. That work is about a first-trimester exam, not the mid-pregnancy anatomy scan, and it does not say a first-trimester protocol replaces the usual 18-to-22-week anatomy scan.
What does the anatomy scan look at?
The baby, the placenta and fluid, and parts of you. ACOG says a standard exam can give information on the fetus's position, movement, breathing and heart rate, an estimate of size and weight, the amount of amniotic fluid, the location of the placenta and the number of fetuses. The practice parameter sets out the minimum anatomy to be looked at. That covers the head, face and neck, including parts of the brain and the profile; the heart, with several standard views; the abdomen, including the stomach, bowel, bladder and where the cord enters, and how many vessels the cord has; the spine; and the arms, legs, hands and feet. Where the placenta sits relative to the cervix is documented too. Sex is not a required item. The parameter lists the external genitalia only if medically indicated or if you want to know, and ACOG says it may be possible to tell the sex if the fetus is in a good position.
How is the anatomy scan done?
Most often across your belly. MedlinePlus describes lying on your back while gel is spread on your belly and a handheld probe is moved over it. The probe can also be placed in the vagina, ACOG says, depending on which images are needed and why. MedlinePlus says there may be some discomfort from pressure on a full bladder, the gel may feel slightly cold and wet, and you will not feel the ultrasound waves. Some instructions call for a full bladder, which ACOG says creates a window for clearer images through the abdomen. A fair question when the scan is booked is whether this clinic wants one for this visit.
What are the measurements on the report?
Most are standard measurements of the baby, used to estimate age and size. The practice parameter names the biparietal diameter, head circumference, abdominal circumference and femur length, and says fetal weight can be estimated from measurements like these. The parameter gives an accuracy of plus or minus 7 to 10 days for a gestational age estimate made between 14 weeks and 21 weeks 6 days, and says even the best fetal weight methods can be off by as much as 15 percent. It says a pregnancy should not be redated once an accurate earlier scan is available for comparison, so the earlier report can still matter at this visit. What a number means for you is a question for the clinician who reads the report with you.
What can an anatomy scan not show?
It cannot find everything. The practice parameter says it is not possible to detect all structural congenital anomalies with ultrasound, though following the standard increases the chance of detecting many. Some views are hard to get. The parameter says a second- or third-trimester scan can be limited by imaging artifacts called acoustic shadowing, and that the report should then document the limitation. Before about 18 weeks, the baby's size, position and movement, abdominal scars or a higher body mass index can also make some structures hard to see. The parameter also notes that where the placenta appears to sit early in pregnancy may not match where it is at delivery. MedlinePlus says normal results may vary slightly and points to your provider for what your own results mean.
What happens if a follow-up scan is suggested?
The reasons vary. The practice parameter says a follow-up exam may be helpful when a scan had a technical limitation, and that a more detailed anatomic exam may be needed if something is found or suspected on the standard exam. ACOG describes specialized exams for when a problem is suspected based on risk factors or other tests, such as tracking growth over the pregnancy. MedlinePlus says the number of scans depends on whether an earlier scan or blood test found something that needs follow-up. For growth scans, the parameter says they should be no more often than every 2 weeks, because shorter gaps can blur real growth with technical variation. You could ask what the next scan is meant to look at, whether it is a limited, standard or more detailed exam, and whether that clinic will have this report.
Is the scan safe, and what about keepsake ultrasounds?
There is currently no evidence that ultrasound harms a developing fetus, ACOG says, while noting that effects could be identified in the future. For that reason it recommends exams only for medical reasons by qualified professionals and says casual use should be avoided. MedlinePlus says current techniques appear to be safe and that ultrasound does not involve radiation. Keepsake scans are a different matter. As the practice parameter notes, the FDA considers promoting, selling or leasing ultrasound equipment for keepsake fetal videos an unapproved use of a medical device.
Why keep the anatomy scan report with the rest of your records?
Because it is the lasting record, and comparing scans can help. The practice parameter says there should be a permanent record of the exam and its interpretation, that the official final report belongs in the medical record, and that comparison with prior relevant imaging may prove helpful. The images are labeled with the facility that made them and kept according to clinical need and that facility's requirements. If the scan was done at an ultrasound clinic and your visits are with a midwife, a fair question is whether the final report has reached your midwife, whether they have your earlier scan, and how you can get a copy.
Sources
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says you should have at least one standard ultrasound exam during pregnancy, which usually is performed at 18 to 22 weeks of pregnancy.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says a standard ultrasound exam checks the fetus's physical development, screens for major congenital anomalies and estimates gestational age.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says that during an ultrasound exam a transducer sends sound waves through the body, the waves bounce back like echoes, and the transducer receives these echoes, which are turned into images viewed on a video screen.
- ACOG Practice Bulletin No. 175: Ultrasound in Pregnancy (December 2016, developed with the American Institute of Ultrasound in Medicine), abstract: ACOG's Practice Bulletin No. 175, developed with the American Institute of Ultrasound in Medicine, says obstetric ultrasonography is an important and common part of obstetric care in the United States.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section II.B, PDF p. 2): The joint practice parameter says an obstetrical ultrasound in the second or third trimester includes an evaluation of fetal number, cardiac activity, presentation, amniotic fluid volume, placental position, placental cord insertion site, fetal biometry, anatomic survey and growth, and that the patient's cervix, uterus and adnexa should be examined.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.g, PDF p. 8): The joint practice parameter says fetal anatomy may be adequately assessed by ultrasound after approximately 18 weeks gestational age, and that before this time some structures can be difficult to visualize because of fetal size, position, movement, abdominal scars or increased patient body mass index.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says a first-trimester ultrasound exam is not standard because it is too early to see many of the fetus's limbs and organs in detail, and that an exam done this early is used to estimate gestational age, count the number of fetuses and check the fetus's heart rate, among other uses.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says many women will have the length of their cervix measured by vaginal ultrasonography around 20 to 24 weeks of pregnancy.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says a standard ultrasound exam also can provide information about the fetus's position, movement, breathing and heart rate, an estimate of the fetus's size and weight, the amount of amniotic fluid in the uterus, the location of the placenta and the number of fetuses.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.g, PDF pp. 8–9): The joint practice parameter lists the minimal elements of a standard examination of fetal anatomy, including the head, face and neck (among them the lateral cerebral ventricles, cerebellum, upper lip and profile), the heart (including the four-chamber view and the outflow tracts), the abdomen (including the stomach, bowel, urinary bladder, umbilical cord insertion site into the fetal abdomen and umbilical cord vessel number), the spine, and the presence of legs, arms, hands and feet.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.c, PDF p. 6): The joint practice parameter says the placental location, appearance and relationship to the internal cervical os should be documented.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.g.vi, PDF p. 9): The joint practice parameter lists external genitalia in the fetal anatomic survey only if medically indicated or the patient wants to know.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says that if the fetus is in a good position, it may be possible to tell the sex.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says you lie on your back, a clear, water-based gel is spread on your belly and pelvis area, a handheld probe is moved over the area, and the gel helps the probe transmit sound waves.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says the transducer is either moved across your abdomen (transabdominal ultrasound) or placed in your vagina (transvaginal ultrasound), and that the type of exam depends on what types of images are needed and why the exam is being done.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says there may be some discomfort from pressure on the full bladder, the conducting gel may feel slightly cold and wet, and you will not feel the ultrasound waves.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says that for a transabdominal exam you may need to drink several glasses of water during the 2 hours before the exam to fill your bladder, and that a full bladder creates a window through which structures can be seen more clearly.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.d–e, PDF p. 7): The joint practice parameter describes measuring the biparietal diameter, head circumference, femoral diaphysis length and abdominal circumference, and says fetal weight can be estimated from measurements such as these.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.d, PDF p. 7): The joint practice parameter says gestational age assessment by ultrasound in the early second trimester (between 14 0/7 and 21 6/7 weeks) is based on a composite of fetal biometric measurements and has an accuracy of ±7-10 days.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.e, PDF p. 7): The joint practice parameter says even the best fetal weight prediction methods can yield errors as high as ±15%.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.d, PDF p. 7): The joint practice parameter says the pregnancy should not be redated after an accurate earlier scan has been performed and is available for comparison.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section I, PDF p. 2): The joint practice parameter says it is not possible to detect all structural congenital anomalies with diagnostic ultrasound, and that adherence to the parameter will increase the likelihood of detecting many fetal abnormalities.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.g, PDF p. 8): The joint practice parameter says a second or third trimester scan may pose technical limitations for an anatomic evaluation due to imaging artifacts from acoustic shadowing, that the report should then document the nature of the limitation, and that a follow-up examination may be helpful.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.c, PDF p. 6): The joint practice parameter says apparent placental position early in pregnancy may not correlate well with its location at the time of delivery.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says normal results may vary slightly and to talk to your provider about the meaning of your specific test results.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.g, PDF p. 8): The joint practice parameter says a more detailed fetal anatomic examination may be necessary if an abnormality or suspected abnormality is found on the standard examination.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says a specialized ultrasound exam is performed if a problem is suspected based on risk factors or other tests, and gives the example that if there are signs the fetus is not growing well, its growth rate can be tracked with specialized exams.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG describes three types of prenatal ultrasound exams: standard, limited and specialized, and says a limited exam is done to answer a specific question.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says how many ultrasounds you will need depends on whether a previous scan or blood test has detected problems that require follow-up testing.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section IV.B.2.e, PDF p. 7): The joint practice parameter says scans for growth evaluation should be performed no more frequently than at 2-week intervals, because a shorter interval may cause confusion over whether measurement changes are due to growth or to technical variation.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says there is currently no evidence that ultrasound is harmful to a developing fetus, but that it is possible effects could be identified in the future.
- ACOG: Ultrasound Exams (FAQ025, published June 2017, last reviewed October 2025): ACOG says it is recommended that ultrasound exams be performed only for medical reasons by qualified health care professionals, and that casual use of ultrasound during pregnancy should be avoided.
- MedlinePlus Medical Encyclopedia: Ultrasound pregnancy (review date 3/17/2026): MedlinePlus says current ultrasound techniques appear to be safe and that ultrasound does not involve radiation.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Fetal Safety, PDF p. 10): The joint practice parameter notes that the promotion, selling or leasing of ultrasound equipment for making keepsake fetal videos is considered by the U.S. Food and Drug Administration to be an unapproved use of a medical device.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section V, PDF p. 9): The joint practice parameter says there should be a permanent record of the ultrasound examination and its interpretation, that comparison with prior relevant imaging studies may prove helpful, and that an official interpretation (final report) should be included in the patient's medical record.
- ACR–ACOG–AIUM–SMFM–SRU Practice Parameter for the Performance of Standard Diagnostic Obstetrical Ultrasound (revised 2023) (Section V, PDF p. 9): The joint practice parameter says images should be labeled with the patient identification, facility identification and examination date, and that retention of the images should be consistent with clinical need and relevant legal and local health care facility requirements.
- Obstetrics & Gynecology: Anomaly Detection With an Expanded Standardized First-Trimester Fetal Anatomic Ultrasound Screening Protocol (epub 2026 Aug 27); PubMed 42659612: An August 2026 Obstetrics & Gynecology study (epub 2026 Aug 27; PubMed 42659612) evaluated an expanded standardized first-trimester fetal anatomic ultrasound screening protocol (StaFFAUS) at 11 6/7-13 6/7 weeks versus ISUOG Detailed and Minimum first-trimester protocols for anomaly detection.
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