Amniocentesis or chorionic villus sampling in multiple gestations? Experience with 500 cases

500 women with multiple pregnancies underwent amniocentesis or chorionic vi llus (CV) sampling at our department between January 1988 and July 1997. Th e aim of this retrospective study was to evaluate the laboratory aspects an d the consequences of discordant results in these pregnancies in relation t o the method of sampling. Uncertain results in one or both samples, requiri ng further investigation were more frequent in CV samples (eight times in 1 63 paired samples, 5 per cent) than in amniotic fluid (AF) samples (once in 298 paired samples, 0.3 per cent). Sampling one fetus twice (erroneous sam pling) was seen only once among 163 pregnancies with two CV samples in our study. Cross contamination due to mixed sampling was discovered in two of s even pregnancies that underwent DNA diagnosis in CV and might be a rather r egular occuring phenomenon. In none of the 500 pregnancies mixed sampling c aused diagnostic dilemmas. A third sampling problem, maternal cell contamin ation caused a diagnostic problem once among the AF samples. Selective feta l reduction appeared safer after CV sampling than after amniocentesis. Subs equently, CV sampling instead of amniocentesis has become the method of cho ice for prenatal diagnosis in multiple pregnancies in our department. Copyr ight (C) 1999 John Wiley & Sons, Ltd.