Generality
The morphological ultrasound is a diagnostic test that allows to evaluate the state of fetal health and the regular evolution of pregnancy. The investigation is performed in the second trimester, placing an ultrasound probe on the abdomen of the expectant mother.
During the examination, the specialist doctor checks fetal growth by measuring biometric parameters (including the head, abdomen and femur), the movements of the unborn child and the implantation position of the placenta.
The morphological ultrasound allows to verify the exact relationship between the quantity of amniotic fluid and the size of the fetus, as well as to establish the sex of the baby.
What is that?
The morphological ultrasound is a fundamental examination in the prenatal diagnosis, as it allows to evaluate in advance if the unborn child has developmental anomalies or may be predisposed to specific pathologies.
The "execution of this" investigation is indicated between the nineteenth and twenty-second gestational week, a period in which the relationship between the size of the baby and the quantity of amniotic fluid is optimal. Secondly, after this time limit, recourse to termination of pregnancy (abortion) is no longer admissible by law, even in the presence of serious malformations of the fetus.
In addition to the study of the morphology, the ultrasound performed in the second trimester of gestation also provides for the evaluation of the biometry of the fetus (ie its growth), of the placental insertion and of the quantity of amniotic fluid.
What is meant by prenatal diagnosis?
- The prenatal diagnosis is the set of instrumental investigations and laboratory tests which aim to recognize the pathologies affecting the child, before birth.
- This "multidisciplinary approach allows to verify or exclude the presence of any fetal anomalies and / or malformations, genetic syndromes, metabolic diseases and secondary conditions to infections contracted by the mother during gestation.
- The prenatal diagnosis allows to provide the correct information about the progress of the pregnancy and to reassure the future parents.
- As regards the ultrasound examination, the purpose of the investigation changes in relation to the gestational period: in Italy, usually, three ultrasound scans are performed during pregnancy, one in each trimester.
- During the second trimetre, morphological ultrasound is aimed at evaluating the fetal anatomy (screening for malformations).
What is it for?
The morphological ultrasound is the second of the three ultrasounds provided by the guidelines issued by the Ministry of Health to check the health of the baby during gestation.
This investigation is important to evaluate the structure of the fetus and its biometry, 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 baby and allows to identify the movements and the heartbeat. 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 implantation site of the placenta, the quantity of amniotic fluid (normoamnios, oligohydramnios or polyhydramnios) and some fetal organs.
Through the morphological ultrasound, parents can also satisfy a particular curiosity, that is to know the sex of the unborn child.
What is evaluated?
During the morphological ultrasound, as a rule, the following anatomical areas are studied:
- Head: The shape of the skull, the size of the brain, the presence of the lateral ventricles and the morphology of the cerebellum are examined. The conformation of the face is checked, with particular attention to the eye sockets, the structure of the ocular tissue, the upper lip and, in general, the fetal profile.
- Chest: the lungs and heart are carefully observed (the way it is positioned, the structure of the four heart chambers, the left and right ventricular-arterial connection, the rate and rhythm of the heartbeat).
- Limbs and spine: the conformation of the rachis is evaluated (useful for ascertaining the total absence of malformations in the spine) and of the long bones of the four limbs, and the presence of hands and feet.
- Abdomen: the structure of the gastrointestinal (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 that compose it are evaluated .
The examination is completed by evaluations regarding some risk indicators of chromosomopathies (called "soft markers"), that is structural malformations affecting the various organs, detectable by ultrasound and associated with disorders in the genetic makeup of the fetus. These anomalies could be symptomatic , in fact, the presence of specific syndromes, such as trisomy 21 (or Down syndrome).
The morphological ultrasound can therefore direct towards the execution of specific tests, which are essential to establish the correct diagnosis.
Note. Morphological ultrasound does not have as its primary objective the search for risk indicators for the evaluation of chromosomal or genetic anomalies. However, if the association of two or more malformations with this method is identified, advice will be given. To deepen the clinical picture, therefore, the execution of more in-depth investigations, such as amniocentesis and CVS, will be indicated.
In the presence of a high risk of fetal malformations, it is also possible to resort to an "early morphological (or pre-morphological) ultrasound scan between the sixteenth and eighteenth week of gestation; this" approach is useful to have a diagnosis in advance and to be in able to deepen the picture in less time with any genetic tests.
How is it done?
Ultrasound is a diagnostic technique that is performed transabdominally, ie 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 that is not audible to the human ear) .
The method is performed by gynecologists, who during their professional training have acquired specific experience on the pathophysiology of the various fetal malformations and their ultrasound identification.
The ultrasound examination allows to explore 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 echoes reflexes. The latter are recorded by the ultrasound probe and are decoded by the central unit of the instrumental apparatus, which transforms the acquired information into two-dimensional images visible on a monitor. Subsequently, the collected data are compared with those of the reference curves: it is therefore possible ascertain whether the size of the fetus matches the expected size.
Usually, during a morphological ultrasound, the search for useful images takes 20-30 minutes.
Reliability and limits
A variable sensitivity between 50% and 80% is attributed to the morphological ultrasound 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 who performs the method;
- Type of equipment used;
- Gestational period in which the examination is performed (some fetal anomalies occur only in the third trimester);
- Amount of amniotic fluid;
- Position of the fetus at the time of examination;
- Thickness of the tissues of the maternal abdominal wall;
- Extent and localization of any anatomical defects.
The limitations of morphological ultrasound include small defects (such as some anomalies of the interventricular or atrial septum of the heart) and slowing 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 the morphological ultrasound, the specialist may encounter difficulties due to the patient's overweight (the thickness of the abdomen can make the images unclear), the excessive amount of amniotic fluid (the ultrasounds reach the structures to be examined less easily) 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 morphological ultrasound is prescribed by the gynecologist between the nineteenth and twenty-second weeks 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 ultrasound scans provided by the Ministry of Health are fully paid for by the National Health Service, as long as they are carried out within the foreseen weeks.
Do you need any preparation?
The morphological ultrasound does not require any particular preparation rules. However, prior to the examination, the patient's informed consent is required. Usually, it is not necessary to fast, nor do you have to drink before the investigation, as required. in pelvic ultrasound scans.
Are there any contraindications?
The morphological ultrasound is not a painful examination for the expectant mother and does not produce harmful effects on the fetus, even in the long term. For this reason, the investigation is considered risk-free.
Other tests associated with morphology
In some cases, morphological ultrasound is associated with other tests, aimed at assessing the state of health of the mother and child. These include fetal echocardiography and the study of maternal-fetal Doppler flowmetry. This last test evaluates the passage of blood between the baby and the placenta through the cord, for an early identification of the risk of gestosis or fetal growth retardation.
In addition, in women who have an increased risk of preterm birth (multiple pregnancies, a patient with uterine abnormalities or previous cervical surgery), a transvaginal ultrasound can be performed to measure the length of the cervix.
