Invasive Diagnostic Testing

Abstract

Invasive diagnostic testing used for chromosomal, Mendelian, metabolic, and congenital infective diseases is represented nowadays by three main procedures: chorionic villous sampling (CVS), amniocentesis, and fetal blood sampling (FBS). The last technique due to deoxyribonucleic acid and polymerase chain reaction (DNA-PCR) analysis is ever less employed. All these techniques imply continuous ultrasound monitoring of the needle insertion in the uterus. Nondirective genetic counseling possibly before pregnancy is mandatory to explain the indications, the procedure itself, the fetal risks, the possibility for misdiagnosis and the time for receiving the results.Although today the risks of fetal loss after CVS and amniocentesis are very low and almost equal (1:500 and 1:800), the introduction in clinical practice of the first-trimester screening by the combined test using the measurement of the fetal nuchal translucency (NT) plus hormone dosages of pregnancy-associated plasma protein (PAPP)-A and free-beta human chorionic gonadotropin (hCG) and the aid of several other soft markers, such as nasal bone, ductus venosus, and tricuspid regurgitation and above all, the recent introduction of noninvasive prenatal screening (NIPS), with analyzing cell-free DNA in the maternal blood have led to a considerable decrease of invasive diagnostic testing. This trend concerns mostly amniocentesis, whereas the importance of CVS is largely increasing, especially if in combination with comparative genomic hybridization array. The increase in CVS procedures implies a more intense request for tutoring of young fellows in the fetal medicine centers specialized in performing it. The CVS is also the procedure chosen for Mendelian and metabolic pathologies, while amniocentesis, being performed in a later period of pregnancy, is mostly employed for congenital infective diseases. In order to avoid termination of pregnancy of pathologic fetuses, the couple can opt for preimplantation genetic diagnosis (PGD), which analyzes a single or more cells of the blastomere or the blastocyst in order to transfer in utero only the healthy embryos.