Comparison between CVS and early amniocentesis
Cederholm and Axelsson's (1997) paper on the relative value of first-trimester transabdominal chorionic villus sampling (CVS) over early secondtrimester amniocentesis (EA) for prenatal diagnosis (PND) is at variance with most published results (Hansen et al., 1992;Henry and Miller, 1992). In Cederholm and Axelsson's report, in a series of 147 amniocenteses, spontaneous loss followed in 6β’8 per cent and repeats reached 19β’0 per cent. (On the other hand, ambiguous results were obtained in 4β’6 per cent in the CVS series of 174 cases, against 0β’7 per cent in EA material; the repeat rate was 5β’2 per cent; and fetal loss occurred in 1β’7 per cent.) With such values, it is not surprising that CVS appeared to fare better than amniocentesis. However, this is not the experience of the large majority of PND centres.
In our lab, for instance, in a series of 1012 amniotic fluids studied in 1996, the 131 collected at 10-13 weeks' pregnancy performed much better: spontaneous loss followed in 0β’8 per cent of the cases and the success rate was 99β’2 per cent, with a mean culture time and result of 10β’1 days.
It would be interesting to try and detect the parameters for such a discrepancy: there will certainly be differences in the structure of the material from each series, which should be thoroughly analysed. We also put much emphasis on the experience of the person doing the EA sampling, on an exact estimation of gestational age, and on the lab's technique and ability.
From our point of view, in agreement with the majority of authors, under good conditions amniocentesis is still safer and performs better than CVS. We have little experience of CVS, but even comparing our EA data with Cederholm and Axelsson's CVS data, we do not feel it acceptable to perform a similar comparative study, since our abortion risk is so small after EA and the physician gets correct information within 7-10 days after sampling. In our opinion, the results published by the MRC Working Party (1991) remain a useful guideline for people working in this field.