Prenatal fetal karyotyping and maternal serum alpha-fetoprotein screening.

Prenatal karyotyping was undertaken in 569 consecutive amniotic fluid samples where the indication for amniocentesis was two sequential raised maternal serum alpha-fetoprotein concentrations. In 475 successful cultures five chromosome abnormalities were found--four constitutional anomalies (47,XXY; 47,XYY; an inherited inv(8) (p23q11); and a de-novo translocation t(6;7) (p11;p22) and a culture-derived anomaly (trisomy 2) found in amniotic fluid cells but not in the fetus aborted because it had spina bifida. Of the pregnancies complicated by constitutional abnormalities, only the pregnancy in which the de-novo translocation was detected was terminated. No chromosome abnormalities were detected in the 17 pregnancies which miscarried after amniocentesis. These results provide little justification for including fetal karyotyping as an essential part of maternal serum alpha-fetoprotein screening programmes.