Counseling for low maternal serum alpha-fetoprotein should emphasize all chromosome anomalies, not just Down syndrome.

In common usage, a low maternal serum alpha-fetoprotein (MSAFP) value is associated with an increased risk of Down syndrome. We have performed amniocenteses for the indication of age-adjusted low MSAFP in 1154 patients and found 13 chromosomally abnormal conceptions. Autosomal trisomies were detected in half the cases. Additional abnormalities included sex-chromosome aberrations, deletions, or triploidy in proportions consistent with those seen in an advanced-maternal-age population. Patients with low serum AFP should be counseled that not only Down syndrome, but other aneuploidies as well, may be diagnosed. The risk quoted should be that of all chromosomal abnormalities, which is about twice the risk calculated for Down syndrome.