What is it, when and by who is doing?
The anomaly ultrasound scan is a detailed scan of the fetus between 18-22 weeks of pregnancy in order to collect information that will improve prenatal care, and provide birth’s information for the better outcome of pregnancy in favor of the mother and the fetus. Prenatal ultrasound represents one of the most important advances in modern obstetrics. Prior to the advent of this technology, the contents of the uterus were essentially a black box. Ultrasound has evolved significantly since Ian Donald et al. first demonstrated its potential value. It provides an effective means of evaluating the fetus from both a structural and a functional perspective. As a consequence, obstetrics has evolved from a discipline that dealt almost exclusively with maternal health concerns to one that also focuses on the health and development of the fetus.
The reliability of the test is 55% for major anatomical abnormalities of the fetus (those requiring surgical repair or leading to some degree of disability). The examination is performed by certified doctors who perform scans on a regular basis, constantly updated, and at the end of the examination can counsel the patients in cases of pathological findings. In my office the examination is performed with the ultrasound machine Voluson S 10 GE Healthcare BT16-photo (1st established in Northern Greece).
Central Nervous System
The sections most commonly employed to look at the fetal anatomy are axial ones, particularly at the level of ventricles and the cerebellum where a plurality of anatomical parts of the brain are examined such as the lateral ventricles, the cavum septum pellucidum , the thalami, the cerebellum, the vermis and the fourth ventricle of the brain. The sagittal and the coronary sections are useful to examine in detail the ventricles and the corpus callosum of the brain.
The forehead, the orbits, the lips, and the ears are found stable after 12 weeks. At a minimum, complete examination requires axial sections to evaluate the orbits and maxilla, a midsagittal section that identifies the nasal bone and demonstrates the profile, and a coronal section demonstrating the lips.
For the examination of the lungs the section of the 4 chambers of the heart is sufficient. In this section the lungs are echogenics and in 18-23 weeks the central 1/3of the chest is covered by the heart and the rest by the lungs. In this section we can measure the circumference of the thorax. The sagittal view of the fetal trunk is useful for the evaluation of the diaphragm that separates the chest from the abdominal cavity.
The basic section is that of the 4 chambers of the heart where 60% of the lesions are discovered, while the aortic the pulmonary artery outflow and the 3 vessels are views where these large vessels and its connections are thoroughly examined. More sections are taken in cases of pathological findings.
The limbs as buds appear for the first time on 8 weeks while the femur and the humerus appear since the 9th week , the tibia /fibula and radius/ulna from the 10th week while the fingers and hands from the 11th week. All bones are found since the 11th week. Body movements are seen from the 9th week and the limb’s from the 11th week. The lengths of the humerus, of the radius /ulna of the femur and of the tibia /fibula are similar and increase linearly. At the ultrasound scan of 18-23 weeks the three parts of each limb should be recognized but only the femur and humerus should be measured. The scan is completed by the examination of the spine and the 3D view of their bones.
The normal development of the anterior abdominal wall depends on the fusion of 4 ectodermic folds (cephalic, urethral, 2 oblique). At 8-10 weeks all embryos show the normal hernia of the middle intestine that appears as an echogenic mass at the base of umbilical cord but which, during the period of 10-12 weeks returns in the abdomen. This process is completed at 11 + 5 weeks so that the normal abdominal anatomy seen in cross-sections is now visible. Thus, the entrance of umbilical cord in the abdomen appears, but the bladder within the pelvis is also depicted, thus excluding the extrophy of bladder and of cloaca.
By ultrasound the stomach is seen from the 9th week. as an echogenic cystic region in the upper left abdomen. The bowel has normally the same echogenicity in all its parts up to the third trimester, when the meconium fills their loops. The liver is less echogenic than lung and is located in the upper abdomen with the left lobe larger in size than the right due to the greater oxygen supply to it. The gallbladder is pear-like in shape, with the stem pointing toward the hepatic hilum (porta hepatis).It is usually located between the right and the left hepatic lobes, and is located to the right of the intrahepatic portion of the umbilical vein and portal sinus. The spleen is in the axial view behind and left of the stomach The abdominal circumference should be measured at the level of the stomach, the liver and the division of the portal vein. In the axial view, the aorta is located on the left and the inferior vena cava on the right of the spine while on the left of the aorta is located the stomach.
The kidneys and the adrenal glands are below the level of the stomach on each side in front of the spine and appear on the 9th week. and in all cases from the 12th week. Their echogenicity is great on 9th week. but decreases with gestational age. The sagital( longitudinal) and the axial ( transverse) sections of the abdomen are better to examine the kidneys. More specifically, in the sagital view their shape is elliptical while in the axial view is oval. They have less echogenicity than the liver and the bowel At 20th week have an ultrasound echogenic capsular region with the cortical region more echogenic than the medullar. With the progress of the gestational age, the fat accumulates around the tissues, increasing the limits and making them more distinct than the surrounding organs. On 26-28 weeks the renal capsules and arcuate arteries may appear. The renal cortex becomes less echogenic in the third trimester, and the capsule is more sharply delineated, making them easier to see The kidney’s length and circumference increases with the age, but the ratio of the kidney to the abdomen is constant at 30% throughout the pregnancy The anterior diameter of the renal pelvis is <5mm 15-19wk., <6mm 20-29wk. <8mm30-40wk. Normal ureters rarely appear in the absence of peripheral obstruction or regurgitation. The bladder is seen from the 11th week. at 80% and over 90% at 13th week.
Placenta , umbilical cord and cervix
We check the position of the placenta, the umbilical cord, the number of vessels contained we measure the length of the cervix and the presence of any dilation to give the probability of preterm delivery.