Mode of ascertainment is critical in assessing safety of percutaneous umbilical blood sampling.

Percutaneous umbilical blood sampling (PUBS) is increasingly utilized for cytogenetic assessment of the fetus. In the present study, outcome of 109 PUBS-derived fetal blood samples were analyzed according to mode of ascertainment: ultrasound-detected anatomic anomalies or intrauterine growth retardation (IUGR). Abnormal chromosome complements were found in 6 of 47 (12.8%) fetuses with anomalies but in only 1 of 62 (1.6%) fetuses with IUGR alone. Perinatal loss in fetuses with anatomic anomalies was 64.4%, compared with only 1.6% in fetuses with IUGR alone. Mode of patient ascertainment is an important factor that must be considered in determining procedure-related risks for PUBS.