Prenatal diagnosis of a number of congenital diseases is possible by amniocentesis in the 14th - 16th week of pregnancy and subsequent analysis of cultured amniotic fluid cells or amniotic fluid supernatant. Parents at risk for a child with a chromosomal disorder, an X-linked disease, a neural tube defect or a metabolic disease may use this new tool in genetic counseling to limit their further offspring to unaffected children by requesting termination of a pregnancy when a fetal abnormality has been detected. The present thesis describes methodological studies in the field of prenatal diagnosis of metabolic diseases and clinical applications of prenatal monitoring in a series of 350 pregnancies with an elevated risk for a chromosomal aberration, an X-linked disease, a metabolic genetic disorder or a neural tube defect