The dilemma of chromosomal mosaicism in chorionic villus sampling—‘direct’ versus long‐term cultures

Abstract
Chromosomal mosaicism is one of several unanswered dilemmas in first‐trimester prenatal diagnosis. We report the course of a pregnancy in which a normal karyotype was detected on direct CVS preparation and fetal blood, 100 per cent trisomy 21 in one long‐term CVS culture, and low‐rate trisomy 21 mosaicism in a second long‐term CVS culture and amniocentesis. The phenotypically normal infant had a 6 per cent mosaicism of trisomy 21. It appears that a persistent low‐rate mosaicism in different tissues may be indicative of the true status of the fetus.