Is the 15-in situ clone protocol necessary to detect amniotic fluid mosaicism?

Our purpose was to evaluate the 15-clone analysis for detecting amniotic fluid mosaicism by the in situ method.

A 10-year review was performed of all amniotic fluid mosaicism cases at two institutions using the in situ method exclusively, with sequential clonal analysis to determine the first and second clone in which the abnormal cell line occurred.

Of the 28,497 amniotic fluid samples, 73 met criteria for amniotic fluid mosaicism by in situ method (0.26%). There were 54 cases (0.19%) with potential clinical significance (23 autosome and 31 sex chromosome mosaicism); 49 of the 54 cases (89%) were detected in the first six clones, including 22 of 23 involving autosomes and 27 of 31 involving sex chromosomes. In one of the six cases detected after clone 6 (46,XX/47,XX,+21) the mosaic cell line was present in 20% of the clones analyzed and was followed by a voluntary termination of the pregnancy. In the other five cases amniotic fluid mosaicism was present in < 20% of the clones; these included one case of 46,XX/47,XX+mar (15% amniotic fluid mosaicism, voluntary termination of pregnancy), two cases of 45,X/46,XY (10% to 12% amniotic fluid mosaicism, both normal at birth), and two cases of 45,X/46,XX (8% amniotic fluid mosaicism, lost to follow-up; 12% amniotic fluid mosaicism, voluntary termination of pregnancy). By limiting the analysis to six clones, approximately 20% of analysis time could be saved per case, but one autosomal amniotic fluid mosaicism case per 10,000 samples could potentially be missed.

Reducing the number of clones analyzed by in situ method could result in increased efficiency, decreased costs, and minimal loss of sensitivity.