INCIDENCE AND OUTCOME OF CHROMOSOMAL MOSAICISM FOUND AT THE TIME OF CHORIONIC VILLUS SAMPLING

OBJECTIVE: Chromosomal mosaicism has been reported in about 1% to 3% o f chorionic villus sampling specimens. This report provides incidence and outcome information that should be useful in counseling patients f ound to have mosaicism on chorionic villus sampling. STUDY DESIGN: A r etrospective analysis of 11,200 consecutive patients undergoing chorio nic villus sampling at the University of California, San Francisco, du ring the period from Jan. 1, 1984, to June 1, 1996, was undertaken. RE SULTS: A total of 140 cases of mosaicism were identified for an incide nce of 1.3%. Follow-up information was available for 130 cases, 26 of which (20%) were confirmed in fetal tissue. Confirmation rates for spe cific types of mosaicism were as follows: autosomal trisomy 7.6%, sex chromosome 25%, structural abnormality 27.3%, and marker chromosome 77 .8%. Neonatal outcome was normal in all cases for which pregnancy cont inued. CONCLUSION: The data indicate that in most cases of chromosomal mosaicism found by chorionic villus sampling the mosaicism is unlikel y to be clinically significant in the fetus.