Generality
Morphological ultrasound is a diagnostic test that allows the evaluation of fetal health and the regular evolution of pregnancy. The investigation is performed in the second trimester, laying an ultrasound probe on the abdomen of the future mother.
During the examination, the specialist doctor checks the fetal growth through the measurement of biometric parameters (including cephalic, abdomen and femur), the movements of the unborn child and the placental implant position.
The morphological ultrasound allows to verify the exact relationship between the quantity of amniotic fluid and the size of the fetus, in addition to establishing the sex of the child.
What is that?
Morphological ultrasound is a fundamental exam in the field of prenatal diagnosis, as it allows us to assess in advance whether the baby has developmental abnormalities or may be predisposed to specific pathologies.
The execution of this survey is indicated between the nineteenth and twenty-second gestational week, a period in which the relationship between the size of the child and the amount of amniotic fluid is optimal. Secondly, after this time limit, recourse to the termination of a pregnancy (abortion), even in the presence of severe fetal malformations, is no longer admissible by law.
In addition to the study of the morphology, the ultrasound performed in the second trimester of gestation also includes the evaluation of the biometry of the fetus (ie its growth), of the placental insertion and of the amount of amniotic fluid .
What is meant by prenatal diagnosis?
- Prenatal diagnosis is the set of instrumental investigations and laboratory tests aimed at recognizing the pathologies of the child before birth.
- This multidisciplinary approach makes it possible to verify or exclude the presence of any abnormalities and / or fetal malformations, genetic syndromes, metabolic diseases and secondary conditions to infections contracted by the mother during gestation.
- Prenatal diagnosis allows you to provide the correct information about the progress of pregnancy and reassure future parents.
- As far as the ultrasound examination is concerned, the aims of the survey change in relation to the gestational age: in Italy, usually, three scans are performed during pregnancy, one in each quarter.
- During the second trimetre, morphological ultrasound is aimed at assessing fetal anatomy (malformation screening).
What is it for?
The morphological ultrasound is the second of the three ultrasounds provided for by the guidelines issued by the Ministry of Health to monitor the health of the child during gestation.
This investigation is important for assessing the structure of the fetus and its biometrics, monitoring its normal development and proportions in order to exclude or ascertain the presence of malformations .
The morphological ultrasound is useful to verify the position of the child and allows to identify its movements and heart rate. From the fourth month of gestation, the examination allows the measurement of the head, abdomen and femur of the unborn child.
At the same time, it is possible to visualize the site of implantation of the placenta, the amount of amniotic fluid (normoamnios, oligohydramnios or polydramnios) and some fetal organs .
Through morphological ultrasound, parents can also satisfy a particular curiosity, that is, become aware of the sex of the unborn child .
What is evaluated?
During morphological ultrasonography, as a rule, the following anatomical districts are studied:
- Head : the shape of the skull is examined, the size of the brain, the presence of the lateral ventricles and the morphology of the cerebellum. The conformation of the face is checked, with particular attention to the orbits, the structure of the eye tissue, the upper lip and, in general, the fetal profile.
- Thorax : the lungs and the heart are carefully observed (the way it is positioned, the structure of the four cardiac chambers, the left and right ventricular-arterial connection, the frequency and rhythm of the heartbeat).
- Limbs and vertebral column : the conformation of the spine is evaluated (useful to ascertain the total absence of malformations of the spine) and of the long bones of the four limbs, and the presence of hands and feet.
- Abdomen : the structure of the gastrointestinal system (liver, stomach and intestine) and genitourinary (kidneys and bladder) is studied. The diaphragm, the anterior abdominal wall and the position of the umbilical cord with the three blood vessels composing it are evaluated.
The examination is completed by assessments on some risk indicators of chromosomopathies (called " soft markers "), ie structural malformations of the different organs, detectable by ultrasound scan and associated with disorders of the genetic makeup of the fetus. In fact, these abnormalities could be symptomatic of the presence of specific syndromes, such as trisomy 21 (or Down syndrome).
The morphological ultrasound can therefore direct towards the execution of specific examinations, essential to establish the correct diagnosis.
Note. Morphological ultrasonography does not have as its primary objective the search for risk indicators for the evaluation of chromosomal or genetic abnormalities. However, if the association of two or more malformations with this method is identified, a consultation will be carried out in this regard. To deepen the clinical picture, therefore, more detailed investigations will be indicated, such as amniocentesis and villocentesis .
In the presence of a high risk of fetal malformations, it is also possible to resort to an early (or pre-morphological) morphological ultrasound between the sixteenth and the eighteenth week of gestation; this approach is useful to have a diagnosis in advance and be able to investigate the picture with possible genetic tests in less time.
How do you do it?
Ultrasound is a diagnostic technique that is performed transabdominally, that is by placing a specific probe on the abdomen, previously sprinkled with gel to improve the diffusion of ultrasounds (high frequency sound waves, falling within the band not audible to the human ear) .
The method is performed by gynecological doctors, who during their professional training have acquired specific experience on the pathophysiology of various fetal malformations and on their ultrasound identification.
The ultrasound examination allows exploring the internal organs of the body, using ultrasounds, produced by the vibration of piezoelectric crystals contained in the probes. The wall of the uterus, the amniotic fluid and the fetal tissues reflect part of these waves, generating a series of reflected echoes. The latter are recorded by the ultrasound probe and are decoded by the central unit of the instrumental apparatus, which transforms the information acquired into two-dimensional images visible in a monitor. Subsequently, the data collected are compared with those of the reference curves : it is therefore possible to ascertain whether the size of the fetus corresponds to those expected.
Usually, during a morphological ultrasound, the search for useful images takes 20-30 minutes .
Reliability and limits
Morphological ultrasound is attributed a sensitivity varying between 50% and 80% in the identification of major fetal malformations, ie those defects that require medical assistance after birth.
The possibility of detecting a major anomaly depends, in fact, on multiple factors including:
- Experience of the operator performing the method;
- Type of equipment used;
- Gestational period in which the examination is performed (some fetal anomalies appear only in the third trimester);
- Amount of amniotic fluid;
- Position of the fetus at the time of the examination;
- Tissue thickness of the maternal abdominal wall;
- Extent and location of any anatomical defects.
The limitations of morphological ultrasonography concern small defects (such as some abnormalities of the interventricular or interatrial septum of the heart) and the slowing down of fetal growth.
The detection of minor anomalies is not, in fact, an objective of this ultrasound examination (due to the intrinsic characteristics of the method). For these reasons, depending on the case, the doctor can indicate the execution of the most suitable diagnostic investigations to establish the differential diagnosis and the management of fetal pathology.
Note. During morphological ultrasonography, the specialist may encounter difficulties due to the patient's overweight (the thickness of the abdomen can make images unclear), the excessive amount of amniotic fluid (ultrasounds reach the structures to be examined less easily) or the position of the fetus. For these reasons, the doctor may decide to proceed with a transvaginal ultrasound examination in order to better visualize the fetal structures close to the probe.
When is it indicated?
The ultrasound morphology is prescribed by the gynecologist between the nineteenth and twenty-second week of gestation. This period is the best to evaluate all the anatomical details and the main vital organs of the fetus, ascertaining the presence of any malformations.
The three ultrasounds provided by the Ministry of Health are fully borne by the National Health Service, provided they are carried out in the foreseen weeks.
Is preparation necessary?
Morphological ultrasonography does not include any particular preparation norm. However, prior to the execution of the examination, the informed consent of the patient is required. Usually, you don't need to be fasting, nor should you drink before the investigation, as required in pelvic ultrasound scans.
Are there any contraindications?
Morphological ultrasound is not a painful test for the future mother and does not produce harmful effects on the fetus, even in the long term. For this reason, the survey is considered risk-free.
Other exams associated with morphology
In some cases, morphological ultrasound is associated with other examinations, aimed at assessing the health status of the mother and child. These include fetal echocardiography and the study of maternal-fetal doppler flowmetry . The latter examines the passage of blood between the child and the placenta through the cord, for an early identification of the risk of gestosis or fetal growth retardation .
Furthermore, in women who present an increased risk of preterm birth (multiple pregnancies, patients with uterine anomalies or previous cervical surgery) it is possible to perform a transvaginal ultrasound to measure the length of the cervix.
