A 41-year-old had a baby with Down syndrome 10 years ago. She is anxious to know the chromosome status of her fetus in a current pregnancy. The test that has the fastest lab processing time for karyotype is

Amniocentesis, cordocentesis, cystic hygroma aspiration, and chorionic villus sampling are techniques of obtaining fetal tissues that are amenable to cytogenetic analysis. Amniotic fluid cells require tissue culture to obtain adequate cell numbers for analysis. Chorionic villi can be harvested directly for extremely rapid diagnosis or can be cultured for higher banding (increased detail). Fetal blood obtained by cordocentesis or percutaneous umbilical blood sampling (PUBS) requires 2 to 3 days of culturing before a karyotype is obtained. Doppler flow ultrasound is used to assess blood flow through fetal vessels but is not a substitute for direct analysis of tissue.