Percutaneous transvesical chorionic villus sampling: an alternative approach to the retroverted uterus. In 458 consecutive chorionic villus sampling (CVS) procedures, we observed a significant influence of uterine position upon sampling efficacy. Compared with anteverted (N = 243) or axial (N = 149) locations, the retroverted uterus (N = 66) was associated with a lower mean sample weight per aspiration (22, 18, and 15 mg, respectively; P less than .01) and a greater frequency of multiple-pass procedures (23, 31, and 52%, respectively; P less than .0001). To improve sampling efficiency in selected cases of uterine retroversion, we adopted a transvesical approach. When compared with transabdominal or transcervical techniques, transvesical CVS had the highest single-pass success rate (33, 33, and 60%, respectively). Only one in 30 transvesical cases required three placental passes, compared with nine of 36 retroverted uteri sampled by either transabdominal or transcervical techniques (P less than .05). The mean transvesical sample weight was 18.7 mg; at least 10 mg was retrieved in all cases. Post-procedure bleeding occurred in four instances and an additional patient suffered a spontaneous loss at 16 weeks' gestation. Aneuploidy was found in four of 30 biopsy specimens, and the remaining pregnancies either have delivered at term (N = 18) or are continuing (N = 7). Our preliminary experience suggests that selected use of this CVS method may improve sampling efficiency without increasing the incidence of complications. 