Rapid karyotyping for prenatal diagnosis in the second and third trimesters of pregnancy.

Direct chromosome preparations were performed on placental villi obtained by ultrasound-guided needle aspiration between 18 and 37 weeks of pregnancy in 53 patients. The sampling yielded a sufficient amount of tissue with a maximum of two, and in most cases one, insertions. Placental biopsy is easily performed in cases of severe oligohydrammnios, where fetal blood sampling is usually more difficult. Direct karyotyping of placental villi is faster than chromosome analysis from fetal blood or application of the pipette method on amniotic fluid cells, and currently represents the most rapid approach to prenatal diagnosis of chromosomal abnormalities from the first to the third trimester of pregnancy.