What is prenatal diagnosis (diagnosis before birth)?
Prenatal diagnosis, as a general concept, can be described as the identification of problems of the fetus. The diagnosis of fetal abnormalities or diseases, as a promising field, has become of wide interest, especially due to the latest advances in engineering science and medicine. If the disease is curable in utero, it provides timely assistance and, if treatment requires emergency postpartum intervention, this gives a chance to prepare all the necessary conditions in advance. Finally, in situations of incurable diseases, such a diagnosis allows the discussion of possible termination of pregnancy.
How is prenatal diagnosis performed?
Today, there are many ways to perform prenatal diagnostics. Some of them are performed by methods that do not involve any risk or discomfort to the mother (non-invasive prenatal diagnosis), while others can pose a danger to the mother and fetus (invasive prenatal diagnosis). This article will briefly describe the non-invasive methods that we use to diagnose the fetus in the womb.
Procedures performed by intervening in the mother’s body for prenatal diagnosis can be called invasive diagnostic procedures. Their method is to get to the uterus, where the baby is, and take samples of the material from the fetus itself, the placenta, or the amniotic fluid. Today, methods such as amniocentesis (puncture of the amniotic membrane to obtain amniotic fluid for analysis), chorionic villus sampling (CVS) or chorionic villus biopsy, fetal blood sampling (cordocentesis), and, in very rare cases, tissue biopsy are used.
What is amniocentesis?
Amniocentesis is the analysis of amniotic fluid, which allows the fetus to move and grow comfortably and help the development of its lungs. Almost all of this amniotic fluid consists of urine produced by the baby’s kidneys after the first three months of pregnancy. Today, the amniocentesis procedure is performed with the help of ultrasound (video 1).
Video 1. Amniocentesis procedure (from our clinic’s practice).
What fetal diseases can be diagnosed with amniocentesis?
Since the amniotic fluid is mainly composed of fetal urine, many cells from the urinary tract enter this fluid. In addition, since the baby passes amniotic fluid through his lungs, the cells of his skin and respiratory tract are also found in the amniotic fluid. Therefore, all tests performed using the material of these cells can be carried out thanks to amniocentesis.
Worldwide, amniocentesis is mainly performed to diagnose chromosomal problems and genetic diseases of the fetus. After taking the amniotic fluid the material is sent in sterile conditions to the genetic laboratory, where, after a series of thorough studies, the results are obtained. By determining the number of chromosomes in the fetus by analyzing amniocentesis-derived amniotic fluid (cytogenetic study), such chromosomal diseases as Down syndrome, Turner syndrome, trisomy 13 and trisomy 18, as well as many other genetically inherited monogenic diseases can be detected. Besides, with the help of more detailed chromosomal studies, it is possible to identify more serious anomalies. With the amniotic waters, obtained by amniocentesis, the full eczema sequencing (detailed analysis of the genetic material) of the fetus can be done. Apart from that, based on the results of ultrasound and the medical history of the baby we can study clinical eczema. Also, the amniotic fluid can determine whether the baby has any infectious diseases (toxoplasma, rubella, cytomegalovirus, syphilis, etc.). For this purpose, it is possible to study both the immunoglobulins in the amniotic fluid and the genetic material (DNA, RNA) of the diagnosed infection. Although amniocentesis is not common in our country, it can also be used to establish the fact of lung development in babies who, for some reason, should be born prematurely.
How risky is amniocentesis?
The procedure of amniocentesis is associated with very low risk if it is carried out correctly by an experienced doctor. The probability of miscarriage due to amniocentesis is about one two-hundredth (1/200). Given that some babies undergoing this procedure have serious abnormalities that are practically incompatible with life from the very beginning, the risk of miscarriage due to amniocentesis in the case of healthy babies will be even less.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is the process of taking samples from the placenta, accompanied by ultrasound. Since the fetus and the placenta come from the same fertilized egg, it is assumed that the genetic structure of the placenta must match the genetic structure of the fetus. Because after the egg is fertilized, and the resulting zygote begins to divide, one part of these dividing cells forms the fetus and the other part-the placenta. That is why it is expected that their genetic composition will be the same. However, it is reported that very rarely (in less than one percent of cases) the genetic structure of the placenta does not always coincide with that of the fetus.
Why is Chorionic Villus Sampling (CVS) necessary?
Chorionic villus sampling (CVS) just like amniocentesis, is used for prenatal genetic diagnosis. Thanks to CVS, it is possible to recognize chromosomal number abnormalities, as well as, by studying molecular genetics, monogenic fetal diseases.
When and how is Chorionic Villus Sampling (CVS) taken?
Compared to amniocentesis, CVS is performed in the earlier weeks of pregnancy. In the world, the CVS procedure is usually performed between 11 and 14 weeks of pregnancy. The choice of week 11 as the start is determined by concerns about the increased likelihood of abnormalities in infants with CVS performed at an earlier date. Given that amniocentesis is performed after the 16th week, CVS allows you to recognize fetal chromosomal diseases earlier than amniocentesis, which makes it possible to plan pregnancy according to the result. CVS, as well as amniocentesis, is performed by taking a sample from the placenta of the fetus using a special catheter (needle) accompanied by ultrasound (video 2).
Video 2. Taking a sample of chorionic villi (chorionic villi biopsy: CVS), (from our clinic’s practice).
The cordocentesis procedure, as well as amniocentesis and CVS, is accompanied by ultrasound. It is the process of taking blood from the fetal umbilical cord. While pregnancy loss in amniocentesis and cardiovascular diseases is one two-hundredth (1/200) percent, with cordocentesis, this risk increases slightly to about 2.5 percent. In the process of cordocentesis, blood taken from the baby’s umbilical cord can be used for genetic studies to detect the presence of fetal infection, as well as to check general blood parameters (for example, for anemia).
Fetal tissue biopsy
Fetal tissue biopsy is the process of taking a biopsy of a baby’s skin, muscle cells, or liver to examine specific diseases. Required and used in very rare cases.