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

Summary. 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%.