Fetal blood sampling in investigation of chromosome mosaicism in amniotic fluid cell culture.

41 pregnancies in which mosaicism had been found on amniotic fluid culture (AFC) were investigated by fetal blood and repeat AFC karyotyping. Results of both investigations, and the infants, were normal in 15 of 16 cases of autosomal trisomy (including trisomies 8, 9, 13, 18, and 21) and in the 8 cases of sex chromosome mosaicism. In 1 case of trisomy 20 mosaicism the fetal blood karyotype and the infant were normal but the repeat AFC showed mosaicism. Abnormality was confirmed in 5 of 11 cases of mosaicism for structural chromosomal rearrangements and in 4 of 6 cases with de-novo supernumerary marker mosaicism. These findings indicate the potential danger of terminating pregnancies because of trisomic mosaicism in AFC, and the importance of identifying the clinical significance of certain chromosome rearrangements which, even in mosaic form, might lead to severe mental and developmental handicap.