What is an Anomaly Scan And How Is It Done?

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Routine tests and diagnostics are a must during pregnancy, as they allow your doctor to keep track of your health as well as the baby’s health. While some of these testing procedures can leave you exhausted, others give you the joy of looking at the baby inside the womb or even listening to its heartbeat.

One such detailed scanning procedure is the Anomaly scan that is performed midway through your pregnancy. Find out more about this procedure and its significance in this MomJunction post.

What Is Anomaly Scan?

The Anomaly scan is a detailed morphology ultrasound scan, also known as 20th-week scan or mid-pregnancy scan, and is carried out between the 18th and 21st weeks of pregnancy (1). In some cases, it is also done after 21 weeks. It checks if the fetus is growing normally and has any congenital abnormalities. That said, it cannot detect every problem (2).

The primary purpose is to check for fetal development.

Is It Necessary To Have An Anomaly Scan?

All women, irrespective of their age, carry a little risk of delivering babies with physical and mental anomalies. The anomaly scan helps to find or rule out such abnormalities (3).

What Does It Look For?

Just like the ultrasound scan, the anomaly scan determines the following (4):

  • Size, growth, maturity and general health of the baby
  • Examines all the fetal organs, stomach, and abdominal wall
  • Gestational age

It may also indicates congenital abnormalities including (5):

  • Anencephaly
  • Cleft lip or palate
  • Spina bifida
  • Congenital heart disease
  • Down syndrome
  • Edward’s syndrome
  • Patau’s syndrome

Cardiac abnormalities could be missed around the 20th week, but a repeat scan for fetal echocardiography around the 24th week determines the cardiac structures in detail.

Most of the times, the scan shows normal development of the baby, and only a sonographer can detect the problem if any.

How To Prepare For An Anomaly Scan?

The anomaly scan is a normal procedure that requires no special preparations. Some tips could make the scan comfortable, quick, and efficient for you.

  • Relax before the scan and reach the diagnostics center early to make yourself comfortable.
  • You should have a full bladder as the scan cannot give accurate results when performed on an empty bladder. Wait until the bladder is full.
  • During the scan, you will need to expose your abdomen from the navel to pubic bone. Therefore, wear some loose clothing that is easily adjustable.
  • Do not wear any ornaments or accessories on your body during the scan.
  • Take all your reports and medical records while going to the diagnostic center.

Keep reading to know the exact procedure.

How Is The Anomaly Scan Done?

It is carried out by a specially trained sonographer in a dimly lit room to get good images of the baby (5).

  • The sonographer will apply a water-based gel on your abdomen to begin the procedure.
  • A handheld probe is run over the tummy to examine the fetal body. The probe collects the sound waves and creates the image of your baby on the ultrasound screen.
  • The sonographer may apply a little pressure on the tummy for the best view of the baby. It might be a bit uncomfortable, but it will not hurt the baby.
  • The scan takes around 30 minutes, and the sonographer will show you and talk to you about the different parts of the baby as well as the baby’s heartbeat.

Sometimes you may not get a clear picture if the fetus is lying in an awkward position or moving around a lot, or if your body tissue is dense or you are obese.

What Does The Anomaly Scan Show?

The main purpose of the scan is to check if the baby is developing without any abnormalities. The sonographer will look for the following (6):

  • Shape and structure of the baby’s head and brain. At this stage, severe brain problems are identified.
  • Face, to spot cleft lip although it is difficult to see it clearly.
  • The spine, along its length and cross-section, to check if the bones are aligned properly and if the skin is covering the back properly.
  • Abdominal wall to check if all the internal organs are covered in the front.
  • Heart, if its top two chambers (atria) and bottom two chambers (ventricles) are equal in size, the major veins and arteries that carry blood, vales that open and close with each heartbeat.
  • Stomach, as baby consumes some amniotic fluid. The scan shows it as a black bubble.
  • Kidneys, to check if there are two, and urine freely flows through the bladder. Even if the baby’s bladder is empty, it fills up as you take water before the scan, and the little one urinates every half an hour around this period.
  • Hands, arms, legs, and feet along with fingers and toes.
  • The position of the placenta.
  • Blood vessels of the umbilical cord to check if enough blood is flowing through it.
  • If there is enough amniotic fluid for the baby to move freely.

The sonographer also takes anomaly scan measurements to determine the:

  • Head circumference (HC)
  • Abdominal circumference (AC)
  • Length of the humerus or arm bone
  • Length of the femur or thigh bone

The measurements should be similar to what is expected for your baby around that week. It also depends on the due date that is established as per the dating scan. In case it is your first scan, it is also helpful in determining the due date. In addition to this, the scan may also be able to detect some anomalies.

What Abnormalities Can Be Detected In The Anomaly Scan?

The sonographer will observe the images for a wide range of fetal abnormalities, some of which are normal and treatable. Some others may be severe and also fatal for the baby.

Following is the list of conditions that can be seen in the scan and their chances of being detected (7) (8):

  • Anencephaly (absence of the head top) – 99%
  • Cleft lip or palate
  • Hydrocephalus (extra fluid in the brain) – 60%
  • Gastroschisis (defect of the abdominal wall in which the intestines protrude) – 90%
  • Exomphalos (defect of the abdominal wall in which liver and bowel protrude) – 90%
  • Spina bifida (open spinal cord) – 90%
  • Lethal dysplasia (missing or short limbs) – 90%
  • Missing or abnormal kidneys – 85%
  • Diaphragmatic hernia (protusion of abdominal content in the thorax via a hole in the muscle dividing the chest and abdomen) – 60%
  • Heart problems such as defects in the chambers, vessels, and valves – 25%
  • Down syndrome – 40%
  • Patau’s or Edward’s syndromes (chromosomal abnormalities)

Some conditions, including heart defects and bowel obstructions, are not detected until late pregnancy. Anomaly scan will rule out or detect all the above conditions in time and allow the doctor to plan the further course of action.

What Happens If The Anomaly Scan Is Not Normal?

Know that the anomaly scan result is not always 100% accurate, and observations may sometimes go incorrect. If any problem is spotted, your doctor might give you advice on how to deal with the condition.

  • Some problems may need a repeat scan. This is in case the sonographer has not seen everything in detail because of the unfavorable fetal position, or the mother’s dense skin tissue hindering the view. In this case, the scan is repeated around the 23rd week.
  • If a problem is suspected, you will be given an appointment with a fetal medicine specialist.
  • If your baby is suspected of having a heart problem, you will be taken to a fetal echo scan for a detailed look at the heart.
  • If a severe problem is detected, the doctor gives all the needed support and guides you through the options. Some issues may require surgery or treatment while the baby is still in the womb and some after birth.

Even the thought of the baby having a problem can be overwhelming. But know that not all babies have a congenital problem. If there is a concern, a chain of obstetricians, midwives, pediatricians, and other specialists will support you through it.

Next, we address a few commonly raised queries about this scan.

Frequently Asked Questions

1. Can I have a photo of my scan?

Most diagnostic centers will give the picture of your scan but check with the doctor before the appointment. They may also charge for the picture that is probably printed on a thermal paper and is sensitive to heat.

2. When will I get the results of the scan?

The sonographer will tell you about the visible problems immediately during the scan. However, it depends upon the hospital when to produce the results.

Neither you nor your baby is likely to have any risks from having an anomaly scan. Opting for the scan is good as it helps you get useful information about the baby’s health and take the necessary measures in time. Talk to your doctor to clear any doubts you have before the scan.

Have you undergone the anomaly scan? If yes, please share your experience with us in the below comment section.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
1. Women’s Health Care; The Aga Khan University Hospital
2. Dr Mary Moran; Fetal Anomaly Scan Guidelines; The British Medical Ultrasound Society (BMUS)
3. Antenatal care critical in detecting and correcting foetal abnormalities during pregnancy; Aga Khan University Hospital (2018)
4. Charles H. Rodeck and Martin J. Whittle; Fetal Medicine: Basic Science and Clinical Practice; Page 266
5. 20-week anomaly scan; NHS (2018)
6. Yvonne Cargill and Lucie Morin; Content of a Complete Routine Second Trimester Obstetrical Ultrasound Examination and Report; SOGC CLINICAL PRACTICE GUIDELINE (2009)
7. S Pathak and C Lees; Ultrasound structural fetal anomaly screening: an update; BMJ (2009)
8. Dr Hon Sook Kit; Detailed Fetal Anomaly Scan; Regency Specialist Hospital (2017)