ABSTRACT
The quality of ultrasonography has vastly improved, allowing detection of both gross and increasingly more subtle congenital anomalies and providing accurate guidance for diagnostic procedures including amniocentesis, chorionic villus sampling, fetal blood sampling, and fetal biopsy. The status of preimplantation diagnosis and of prenatal diagnosis using fetal cells or fetal DNA isolated from the maternal circulation is reviewed. One of the main disadvantages of multiple-marker screening was its timing in the second trimester. As a result, our understanding of developmental abnormalities and what may represent normal variation will expand and thereby modify the genetic counseling engendered and what is offered in terms of prenatal diagnosis. The proportion of fetal cells after sorting second-trimester samples was approximately 20 fetal cells per 1000 maternal cells in this study, though other investigators have described such high yields of fetal cells. Couples with a previous trisomic child are thought to have approximately a 1% risk of recurrence and are thus offered prenatal diagnosis.
