Fetal tissue sampling. The San Francisco experience with 190 pregnancies.

Prenatal diagnosis of genetic defects was done using fetal blood sampling in 167 at-risk pregnancies, by fetal skin biopsy in 15 pregnancies, and by fetal liver biopsy in 8 pregnancies. Fetal blood sampling was done by fetoscopy through January 1985 and by sonographically directed percutaneous umbilical blood sampling since then. In our series, cytogenetics has become the major indication for fetal blood sampling, increasing from 6% of the cases with fetoscopy to 48% with umbilical blood sampling. Fetoscopy provided pure fetal blood in 61% of cases while umbilical blood sampling provided pure fetal blood 97% of the time. The corrected risk of fetal demise after percutaneous umbilical fetal blood sampling was 2% and after fetoscopy was 4%.