Prenatal karyotyping using fetal blood obtained by cordocentesis: rapid and accurate results within 24 hours.

Spontaneously-dividing nucleated erythrocytes present in prenatal cordocentesis samples can be used to obtain fetal karyotype information within 24 hours. Following a modified protocol we performed rapid chromosome analysis on fetal blood from 70 second- and third-trimester fetuses. In all cases cordocentesis was performed following detection of ultrasound abnormalities. Cytogenetic diagnoses were obtained within 24 hours from 59 (84.3%) of the 70 samples. Follow-up chromosome analysis from mitogen-stimulated cultures showed concordant results in 57 of the 59 successful cases. In one case a mosaicism for 45, X[4]/46,X,i(X)(q10)[4] was detected in unstimulated harvest while mitogen-stimulated preparations showed only the 46,X,i(X)(q10) line. In the second case, a marker chromosome was identified in all 5 cells analyzed from the unstimulated harvest while mitogen-stimulated cultures showed only 4 out of 100 cells with the marker.