Transabdominal Chorionic Villus Sampling
Two techniques for TA sampling are presently used. In the
single-needle approach a 20-gauge 15 cm needle is used.
Alternatively, some operators perform a double-needle
technique that uses an outer guide needle (18-gauge thin
wall or a 16- to 17-gauge standard spinal needle) and a
smaller sampling needle (20 gauge).24 In general, a 3.5-inchlong
needle 9cm is sufficient for most patients, but a 5- or 6-inchlong
needle 15 cm should be available for very obese women.