Prenatal screening: invasive diagnostic approaches.

INTRODUCTION: Fetal invasive procedures provide ovular samples that are helpful in establishing diagnosis, etiology, and prognosis when ultrasonography and MRI show a central nervous system (CNS) anomaly or when the fetus is at high risk of such pathology. PROCEDURES: Invasive procedure techniques are amniocentesis, fetal blood sampling (FBS), and chorionic villous sampling (CVS). They provide material for fetal DNA, biochemical analysis, or identification of various infectious agents. COMPLICATIONS: The main complications are miscarriage and premature delivery. Counseling the parents about the risks and benefits of these procedures is therefore mandatory. DISCUSSION: Amniocentesis may be performed as early as 15 weeks' gestation and is the most widely used invasive technique. FBS is performed after 18 to 20 weeks of pregnancy and CVS may be carried out after 11 weeks. Indications for invasive techniques include DNA and cytogenetic analysis, diagnosis of neural tube defects, identification of infectious agents (toxoplasmosis, cytomegalovirus, rubella, and varicella), and etiology of intracerebral hemorrhage (fetal platelets and coagulation factors).