INVASIVE PRENATAL PROCEDURES - IS BACKUP TISSUE SAMPLING INDICATED

Prenatal karyotyping was performed on 136 patients because of one or m ore abnormalities detected on ultrasound, A total of 188 specimens was obtained which included fetal blood, amniotic fluid and chorionic vil lus, In 52 patients a second or 'backup' sample was obtained and in 10 0% cytogenetic analysis was successful. In contrast, failure to obtain a result occurred in 4 (4.7%) of the remaining 84 patients where a se cond sample was not obtained. In the event of primary sample failure, backup sampling not only improves the karyotype yield, but obviates th e need for a second pass procedure with its attendant risks.