Chorionic villus sampling (CVS) is still considered to be an applied research method and its safety is under evaluation in randomized trials. Moreover, no knowledge is available about the comparative efficiency and risks of transcervical and transabdominal chorionic villus sampling. A preliminary analysis of the first 639 consecutive cases of an ongoing trial in which cases are randomized between transcervical and transabdominal aspiration techniques shows: (a) an overall sampling success rate of greater than 99% obtained by both techniques; however, the number of repeat insertions of the sampling device was higher for the transcervical route; (b) a significant shift towards lighter tissue samples for the transabdominal route; however, very light specimens, less than 10 mg, were equally distributed in both groups; and (c) approximately 10% of cases underwent a different procedure from the allocated one because of an anatomical or clinical contraindication, with a higher rate of deviation for the transcervical technique.