Cytogenetic findings in 1250 chorionic villus samples obtained in the first trimester with clinical follow-up of the first 1000 pregnancies.

First-trimester chorionic villus sampling (CVS) was performed in a series of 1250 pregnancies. The direct method of karyotyping was successful in 1205 (96.4%). Abnormal laboratory findings resulted in 60 terminations of pregnancy (4.8%). In addition, six unexpected balanced chromosome rearrangements were detected. False-positive cytogenetic findings occurred in 2.3%, comprising 22 with mosaicism confined to the trophoblast, and a further six non-mosaic false-positive discrepancies were detected, four after termination of pregnancy. The outcome of the first 1000 pregnancies is known in all but one. There were no false-negative findings. Of 947 pregnancies meant to be continued, 34 (3.6%) ended in pregnancy loss before 28 weeks gestation. However, obstetricians with an experience of over 150 procedures had a pregnancy loss of 1.3%.