MacKenzie W E, Holmes D S, Webb T, Whitehouse C, Newton J R
Am J Obstet Gynecol. 1986 Jan;154(1):34-9. doi: 10.1016/0002-9378(86)90388-1.
A randomized trial involving 200 transcervical chorionic villus samples taken with three different cannulas was undertaken. In terms of karyotype recovery and ease of insertion the aluminum cannula performed best although the placental site influenced the ability to recover villi for all cannulas.