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.


Amniocentesis is performed most of the time by two
operators. There are several technique options and at
least three hands are needed: one for the ultrasound
probe, one for the needle, and one to two for the syringe
to withdraw amniotic fluid. Most of the time, the main
operator holds the probe and the needle in each hand.
The assistant adapts the syringe and withdraws the fluid