Banding resolution of amniotic cell chromosome preparations for prenatal diagnosis.

Fifty consecutive routine female karyotypes of amniotic fluid cells were analyzed to determine: (1) the banding resolution of each metaphase in routine preparations, (2) whether all haploids in the same metaphase had the same level of banding resolution, and (3) which chromosomes showed the least/most variation in regard to banding resolution. For each karyotype, the number of dark bands for each right-hand-side chromosome were counted and compared with an ideogram (ISCN 1985). Banding resolution was separated into three groups: 400-band, 550-band, and 850-band. It was found that all 50 metaphases showed at least a 400-band resolution, and 1 metaphase showed a banding resolution between a 550-band and 850-band level. Although the chromosome preparations were sufficient for routine purposes, additional effort and banding techniques are required to detect small chromosomal abnormalities that require a higher level of resolution.