Prenatal Diagnosis, Where and How: No Way Out?

Abstract

ABSTRACT Prenatal diagnosis is the branch of medicine and in particular of obstetrics, that studies and applies the techniques that reveal the normality or the presence of diseases of various kinds, in the fetus. All the techniques of prenatal diagnosis are performed during pregnancy and may be invasive or less. Among the best known, amniocentesis is the most exploited technique nowadays to highlight the possible presence of chromosomal disorders in the fetus, but also infections and genetic diseases such as thalassemia, cystic fibrosis, hemophilia, spina bifida, albinism. Amniocentesis consists of taking an amniotic fluid sample which is then analyzed. Fetal cells suspended in the withdrawn liquid allow us to reconstruct the chromosome map of the fetus and then to confirm or not its normality. Genetic testing, however, are not able to recognize the physical or mental characteristics of the unborn child which are the result of the interaction between multiple genes and the environment. Amniotic fluid makes possible to perform other types of analysis, more or less complex, and it is also possible to store the amniotic stem cells. Similar to amniocentesis as a principle but different as a technique, is chorionic villus sampling (CVS), in which the cells can be put in culture to show their normality, but they are cells taken outside from the gestational chamber (chorionic villi). These are invasive techniques (the fluid is taken by puncture in both cases), but there are also noninvasive techniques. The development of ultrasound, for example, has made it possible to develop some highly sensitive diagnostic techniques, such as the first trimester combined test [bitest and nuchal translucency (NT)], the ‘quadruple’ test, and lately the SCA test in the second trimester, all based on the ultrasound measurement of anatomical and functional parameters of the fetus and on the results of blood tests. These are all screening tests, then they do not give a definite answer but they have a statistical value (very accurate) that can direct toward diagnostic tests. Recently, an extremely sensitive test for the most common aneuploidies and in particular Down syndrome has been proposed to be performed on maternal blood. This test (called fetal DNA testing) is based on the count of fragments of specific chromosomes (21 in the case of Down syndrome) in maternal blood. Although not belonging to diagnostic tests but to probabilistic ones, this test is absolutely the most accurate so far available, with values around 99.99% sensitivity and 0.2% false positives. Also ultrasound in the second trimester of pregnancy (also called morphological ultrasound) that can detect any malformation or fetal abnormality and fetal echocardiography, which analyzes sonographically the fetal heart not only anatomically but also from the dynamic-functional point of view, may be considered methods of prenatal diagnosis. This technique cannot identify genetic diseases. How to cite this article Borruto F, Treisser A, Comparetto C. Prenatal Diagnosis, Where and How: No Way Out? Donald School J Ultrasound Obstet Gynecol 2014;8(3):293-310.