• Register
  • Login
  • Bookmark this page!
Skip Navigation LinksHome Page    >    Ultrasound - system scan
 
 
Pregnancy links...
Health links...
Genetics links...
Medical links...
Other links...
 

Ultrasound - system scan

What is ultrasound and what is its purpose?

This is an imaging test carried out for the purpose of diagnosing several types of defects in organs and in the structure of the body and in cases of intrauterine growth retardation. It is important to note that the test cannot detect functional problems in the fetus such as mental retardation, and there are also certain defects that cannot be detected by ultrasound.

Two system ultrasound scans are usually performed during pregnancy (health organizations usually fund only one scan), along with monitoring progress at the beginning of and towards the end of the pregnancy.

  • First system scan - performed between the 15th and 16th week of gestation.

  • Second system scan - usually performed between the 22nd and 24th week of gestation.

The examination is used in a number of situations:

  • It monitors the development of the fetus and the progression of the pregnancy. For example, ectopic pregnancies (outside the uterus), gestational age, number of fetuses, normal fetal growth, location and structure of the placenta, heart rate and breathing movements and the amount of amniotic fluid can all be shown on the scan.

  • Ultrasound examination is an accessory for the physician that helps him to decide whether or not to recommend invasive diagnostic tests such as amniocentesis, chorionic villus sampling, etc.

The scan can identify certain defects in the structure of the body and the various organs, and other fetal problems such as abnormal growth rate.

Abnormal findings in the ultrasound examination

The purpose of the test is to identify defects in the fetus, but not all the defects that appear on the ultrasound have health implications. Some may only have statistical significance such as an increased risk for other problems. It is therefore important to differentiate between the following terms:
  1. defects

  2. ultrasonographic signs (signs visible on ultrasound that are not defects).



Defects

Defects in the structure of certain fetal organs that can impair the function of the organs, such as heart defects, defects of brain structure, supernumerary digits, cleft lip, etc., can be detected by ultrasound. Such findings are of great medical importance, and all aspects should be considered:

  • multi-disciplinary counseling, a geneticist and an expert in the field of the defect will consider the severity of the defect and its implications for the normal functioning of the affected organ, the prognosis (possibility of repair), the need for treatment/surgery, and whether there will be any long-term effects after repairing the damage.

  • The possibility that the defect may be part of a syndrome (i.e. there are other abnormal findings in addition to this particular defect) should be considered. It is especially important to determine whether there are any chromosomal problems, defects in other systems, mental retardation, etc. Such an evaluation is performed by the geneticist based on the type of defect, the family history, presence of other defects, etc.

  • Specific tests should be offered in order to confirm or rule out the presence of a syndrome, such as a more complex problem that can involve functional disorders, mental retardation, or defects that cannot be detected by ultrasound.

  • If the defect is not so severe as to warrant termination of pregnancy, the method of follow-up should be decided upon through to and after birth.

Causes of different defects

  • Genetic causes are not necessarily hereditary, but may result from a genetic change in the ovum or sperm cell of the embryo itself. This condition is called a spontaneous mutation.

  • It may be the case that everything is normal from a genetic point of view, but there were problems that interfered with the normal development of one of the organs - for example, a disruption in the blood flow to a certain area (or to the entire body) at a critical stage when the structure of the organ was being formed, an intrauterine infection, or various metabolic disorders such as deficiency of a certain vitamin required for normal development, etc.

Even though not all problems have a genetic origin, the geneticist takes the whole picture into account and his/her work includes differentiation and separation between the different possibilities. Therefore genetic consultation is important for obtaining information about the defect itself in order to determine its cause, the risk for its recurrence, and whether it is genetic or a result of other causes.

Ultrasonographic signs

These are changes in the structure of the fetus that do not directly affect its functioning or esthetics.

This means that they are not important in themselves, but may have statistical implications involving an increased risk for other problems that require attention.

Fetal organs do not develop at the same rate.

There are structural differences between fetuses in the same way that there are differences in the build of adults.

Examples include width of the kidney pelvis, thickness of the neck, length of the femur (thigh bone), etc., which differ among individuals andpresent a statistical risk for other problems irrespective of the organ involved.
It is therefore important to consider a number of aspects when giving genetic counseling:

  • Determining whether the degree of the abnormality (severity of the sign) has or has not exceeded the borderline, and if it has, assessing whether it is of such a degree that it changes status from a "sign" to a defect (with functional disorder). For instance, the widening of the kidney pelvis in excess of a certain limit (depending on the week of pregnancy) may indicate a kidney defect and functional disorder. The width of the brain ventricles up to a certain limit is considered a "sign", after which it becomes a "problem". The presence of increased echoes from the intestines after the 18th week is a sign that may indicate cystic fibrosis and chromosomal syndromes, especially if of long duration, and it may also indicate defects in the digestive tract.

  • The rate at which the statistical risk increases and suggests other problems such as chromosomal syndromes (Down syndrome), etc., should be evaluated. Each sign has implications for an increased risk of specific problems arising from it.

  • The type and severity of the sign must be evaluated. Evaluation of the weighted risk (overall picture) is based on the results of other tests (blood biochemistry screening, nuchal translucency, other ultrasound signs).

  • If there is a high risk for the presence of a syndrome, further tests that can determine the extent of the risk are recommended. These tests are performed through the subject's health organization or the Ministry of Health.

However, for some signs there is disagreement between researchers. They disagree over the exact extent of the increased risk that is indicative of a syndrome, and in some cases whether a risk exists at all. Also, the method of precisely calculating the final weighted risk (in addition to other tests) has not been fully determined. However, in most cases whether or not there is an increased weighted risk, an assessment following consultation determines whether or not further tests are required.

It should be noted that parents' anxiety about ultrasonographic signs revealing an actual problem is completely disproportionate. In most cases, the additional risk for an abnormal fetus is negligible because every pregnancy, even if all tests, including amniocentesis and ultrasound, are normal, have at least a 2% risk for "nasty surprises", including mental retardation.

Common signs: echogenic focus in the fetus' heart ventricles ("golf ball"), slight widening of the kidney pelves, choroid plexus cysts in the ventricles of the brain, two umbilical blood vessels, cysts on the sides of the neck, slight shortening of the femur, slightly increased nuchal translucency, echogenic intestines, etc.

In all such cases, the physician must be consulted and genetic counseling sought based on his decision. Genetic counseling should certainly be recommended in cases of more marked increased nuchal translucency, echogenic intestines seen after the 18th week, if a sign is particularly severe, and when there are other coexisting problems such as an increase in other ultrasound parameters or normal biochemical blood screening but a demonstrated risk in excess of 1:1000. Counseling is also recommended when there are several ultrasonographic signs.

Ultrasound can reveal findings that have two aspects: obstetric problems and genetic problems - for example, a delay in the fetus' growth in the uterus, an excess or a reduced amount of amniotic fluid, etc. In such cases, combined counseling by an obstetrician (from a "high risk pregnancy" department and/or an ultrasound physician) and a geneticist is required.
 
Haven't found what you're looking for? Search for it here:   
Comments (0)





Leave a Comment
Name
Email (will not be published)
Website (optional)
Subject
Your Comment

Line and paragraph breaks are automatic. Some HTML allowed: <a href="" title="">, <b>, <i>, <strike>

Please type the characters you see in the picture:


All content Copyright © 2009-2011, Genetics of Pregnancy Encyclopedia Corporation. All rights reserved.