Genetic diagnosis by chorionic villus sampling before 8 gestational weeks: efficiency, reliability, and risks on 317 completed pregnancies.

Transabdominal chorionic villus sampling (TA-CVS) was attempted in 328 high-risk pregnancies at 6-7 weeks of gestation. Sampling was feasible in 97.7 per cent of cases; chorionic tissue specimens of more than 10 mg were obtained in 94.4 per cent of cases at the first needle insertion and in 100 per cent after a second attempt. Fetal karyotyping succeeded in 99.4 per cent of cases, while no diagnostic failures were reported in enzymatic and DNA analyses. Fetal loss rate in the first 4 weeks after CVS was significantly higher than in the later CVS series (7.2 vs. 2.5 per cent), but 50 per cent of losses were observed within 2 weeks in cases of inviable aneuploidies. A high incidence of severe limb abnormalities (1.6 per cent) was detected in pregnancies intended to continue, confirming the aetiological role of early CVS. Unclear visualization of the placental limits and poor control of the needle path are thought to be the main reasons for the vascular disruption of the chorionic plate, and thereby hypoxic embryo tissue damage. A better selection of cases, together with high-resolution vaginal ultrasound visualization, and analytical techniques requiring a minimal amount of tissue should avoid any teratogenic effect of early CVS.