Cytogenetic studies in fetal blood.

In order to assess the effectiveness and reliability of cytogenetic diagnosis provided by fetal blood, we report the first 186 cases of fetal blood sampling performed for rapid karyotype between 19-37 weeks of pregnancy in our Prenatal Diagnosis Unit. The overall diagnostic success rate was 98%, achieving 100% in the last period of the study. Chromosomal anomalies were detected in 16% (29/182) of the fetuses. In malformed fetuses this rate increased from 8-9% in isolated malformation or markers of aneuploidy to 50% in multiple malformations. In pregnancies in which a previous cytogenetic study in amniotic fluid was inconclusive, fetal blood made it possible to obtain a definitive result, with no discrepancies found at phenotypic follow-up examination. Interestingly enough, one of the four previously defined as pseudomosaicisms was found to be a non-mosaic in fetal blood, and only 1 of 4 mosaicisms was confirmed in fetal blood. In conclusion, cytogenetic analysis of fetal blood samples appears to be effective, rapid and reliable to establish the fetal karyotype in selected cases.