Introduction:
Several diagnostic procedures are done during pregnancy. The goal of these procedures is to identify different parameters of the pregnancy. Fetal congenital anomalies are dangerous and may cause severe complications during pregnancy. Identifying such conditions beforehand can be beneficial for both mother and the fetus. Anomaly scan is done during pregnancy to diagnose such fetal anomalies.
What Is Anomaly Scan?
Ultrasound is a non-invasive imaging modality. In this method, high-frequency sound waves are projected toward the target organs, and the echo is recorded to form an image of the internal structures. The sound waves are transmitted through a device known as a transducer. Transducer is also used to record the bounced-back sound waves from the organs. These sound waves are analyzed, and two-dimensional images of the structures are formed; the most commonly used method for ultrasound in gynecology is the trans-abdominal approach. This method is beneficial for imaging the abdominal structure. Pelvic structures are viewed through the anterior abdominal wall in this method. As a result, several errors may happen. These are:
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As the distance between the transducer and the pelvic region increases, a lower frequency must be used to minimize image distortion.
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The beam degrading effect of the anterior abdominal wall, specifically in obese patients, distorts the images.
The transvaginal approach for ultrasound was first introduced in 1985. This method reduces the distance between the probe and the pelvic structures, allowing the use of higher frequency
The latest modification of ultrasound technology is a three-dimensional image and 4D ultrasound. In three-dimensional ultrasound, three-dimensional images of the internal organs are created. For 4D ultrasound, the number of three-dimensional images captured at a given time is more which helps to create a real-time image of the organs and the fetus. Not only that, the collected information is optimized through different mechanisms like thresholding, magic cut, and volume calculation. More data is obtained and analyzed through computer-guided navigation, and a real-time image is generated. Moreover, multiplayer and multi-axial views of the objects can be re-created.
Ultrasound scans are done mainly in three stages of fetal life.
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Level I Scan: This scanning is done between the 11th to 14th week of pregnancy. In this type of scanning, embryo growth and nuchal translucency (detection of fluid behind the neck) are measured. Abdominal ultrasound methods are used in this process. This procedure is useful to diagnose conditions like Down syndrome and trisomy (presence of extra chromosome) of 18 chromosomes.
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Level II Scan: This is the most important scan to detect various anomalies. Structural anomalies and cardiac and lung anomalies can be detected during this period. This type of ultrasound scanning is between the 18th week to the 20th week. This scan is also known as an anatomic scan.
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Level III Scan: This is also known as a fetal well-being scan. In this type of scanning, the growth of the fetus is measured. Volume measurements of fetal arms, head circumference, and thighs can be done with the help of the 4D ultrasound. Also, the position of the fetus and the blood flow status is determined in this scanning. This type of scanning is usually done during the 32nd week of pregnancy.
How to Detect Different Anomalies?
As already discussed, several anomalies can be detected using such a scan. These anomalies are:
Fetal Nuchal Translucency: In this technique, the translucent area in between the skin and the soft tissue area of the back of the fetal neck is measured. The ideal measurement should not be more than three millimeters. Increased thickness of the nuchal translucency is suggestive of structural or chromosomal abnormalities. Down syndrome (presence of an extra copy of 21 chromosomes) and Edwards' syndrome (presence of an extra copy of the 18th chromosome) is associated with increased nuchal translucency.
Identification of Brain Abnormality: The brain images are obtained in three different anatomical levels. These are cerebellum and cisterna magna level, cavum septum-pellucidum level, and ventricular atria level. Abnormalities at the cerebellum and cisterna magna level suggest Down syndrome. Cystic enlargement of the fourth ventricle is suggestive of Dandy-Walker malformation (presence of fluid in between cerebellum). Chiari II malformation (extension of brain tissue into the spinal cord) also can be identified at this level.
Midline development of the brain structures and its differentiation can be identified at the cavum septum pellucidum level. Holoprosencephaly (a condition that is caused by improper differentiation of the brain) can be identified at this level by ultrasonography. Colpocephaly caused by abnormal development of white matter in the posterior cerebrum is identified at this level. Intracranial hemorrhage and choroid plexus cysts can be identified while scanning at the ventricular atria level.
Identification of Spinal Abnormalities: Visualization of spinal structures is done in three different planes. The most commonly seen spinal cord abnormality is spina bifida. In this condition, the spinal fails to close properly. This can be visible in coronal and transverse plane cross sections. Structural defects of the spinal cord like hemi vertebra, wedge vertebra, and block vertebra lead to the formation of scoliosis and kyphosis (abnormal curvature of the spinal cord). Tumors of the spinal cord like sacrococcygeal teratoma can also be identified.
Identification of Brain Abnormality: The brain images are obtained in three different anatomical levels. These are cerebellum and cisterna magna level, cavum septum-pellucidum level, and ventricular atria level. Abnormalities at the cerebellum and cisterna magna level suggest Down syndrome. Cystic enlargement of the fourth ventricle is suggestive of Dandy-Walker malformation (presence of fluid in between cerebellum). Chiari II malformation (extension of brain tissue into the spinal cord) also can be identified at this level.
Midline development of the brain structures and its differentiation can be identified at the cavum septum pellucidum level. Holoprosencephaly (a condition that is caused by improper differentiation of the brain) can be identified at this level by ultrasonography. Colpocephaly caused by abnormal development of white matter in the posterior cerebrum is identified at this level. Intracranial hemorrhage and choroid plexus cysts can be identified while scanning at the ventricular atria level.
Oro-Facial Abnormalities: Oro-facial abnormalities like cleft lip, cleft palate, and abnormal jaw development can also be identified.
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Identification of Cardiac Anomalies: Four-chamber views are most commonly used for the assessment of cardiac conditions. The condition of the cardiac chambers and the condition of the valves can be accessed. Using a 4D ultrasound scan volumetric data like cardiac output, and rhythmic defects can also be identified. Ventricular Septal Defect (presence of the whole in the wall of the heart) is the most common abnormality found in the fetus. Other than this, valvular defects like aortic stenosis, aortic coarctation (narrowing of the aorta), and ectopia cordis (a condition in which the fetal heart is present outside of the chest ) can also be detected using fetal ultrasound.
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Other than this skeletal abnormality, cognitive and motor function disorders, lung abnormalities, and renal dysfunctions can also be found.
What Are the Precautionary Steps?
Anomaly scans should only be done after advice from the doctor. While doing these types of scans following things should keep in the mind:
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Sex determination following the scan is not permissible in some countries,
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Though such scans are safe but prolonged exposure can be harmful. The exposure time should be kept at less than 30 minutes.
Conclusion:
Identification of fetal abnormalities is useful for fetal and maternal health. This is useful to plan future treatment and surgical protocols. Also, future tests can be done based on the scan reports.
