Prenatal diagnosis and genetic counselling.

Traditionally genetic counselling has been made up of two parts. The first is the establishment of an accurate diagnosis of the disorder, usually in the child of the parents availing themselves of counsel but sometimes in the consultand himself. The second is the calculation of recurrence risks through knowledge or the best possible assumptions about the mode of inheritance of the disease. When the counsellor has made the diagnosis and stated the risks, he may provide further guidance on the severity of the disorder and the likely burden to the family concerned and, if necessary, he may advise on contraceptive methods, adoption, or artificial insemination. But the decision to proceed with a family or curtail reproduction lies with the parents. The advent of prenatal diagnosis has changed this traditional mode in a number of situations. The ability to detect an inborn error of metabolism, chromosome disorder, or congenital malformation in utero early enough to allow termination of pregnancy has added a new dimension to genetic counselling. In place of confronting parents with the choice of planning further childien in full knowledge of high risk of abnormality or limiting their families, it is now possible in a rapidly growing number of disorders to monitor at-risk pregnancies and ensure that children born will not be affected. In a sense this has added a positive element to the former inherent negativeness of genetic counselling. The limitations-if the ethical problems which termination of pregnancy may present to parents are overcome-lie in the technology of prenatal diagnosis: the safety of amniocentesis, the problem of growing amniotic fluid cells, the use of amniotic fluid itself, the number of disorders which may be detected in utero in the early stages of gestation, the certainty of diagnosis, and the extension of the list of disorders capable of diagnosis. This review will be concerned primarily with these facets of prenatal diagnosis, already the subject of several comprehensive reviews (Nadler, 1972; Emery, 1973; Milunsky, 1973).