Invasive prenatal procedures: is 'backup' tissue sampling indicated?

Prenatal karyotyping was performed on 136 patients because of one or more abnormalities detected on ultrasound. A total of 188 specimens was obtained which included fetal blood, amniotic fluid and chorionic villus. In 52 patients a second or 'backup' sample was obtained and in 100% cytogenetic analysis was successful. In contrast, failure to obtain a result occurred in 4 (4.7%) of the remaining 84 patients where a second sample was not obtained. In the event of primary sample failure, backup sampling not only improves the karyotype yield, but obviates the need for a second pass procedure with its attendant risks.