Antenatal diagnosis: a new dimension in genetic counseling.

Antenatal diagnosis has now been accepted as an important aspect of primary care medicine, and counseling patients as to the indications for amniocentesis has become routine. The principal indications are maternal age over 35 years of risk of recurrence of Down syndrome or a neural tube abnormality. Recurrence of sex-linked disorders or of inborn errors of metabolism and presence of balanced chromosomal translocations in parents are less frequent indications. Amniocentesis for cytogenetic analysis and determination of alpha-fetoprotein levels is best performed between 14 and 18 weeks of pregnancy. The scope and limitations of the procedure and its complications should be carefully explained to the parents, as should the risk of the detectable genetic disorder compared with the risk of the diagnostic procedure. On the basis of this information, the parents can make an informed decision for or against amniocentesis.