CVS (chorion villus sampling) involves obtaining a small tissue sample or biopsy from the placenta, which is then analysed in the laboratory for chromosomal and other disorders. The procedure is usually performed between 11 and 13 weeks. Under ultrasound control a fine double barreled needle is inserted through the abdominal skin (after local anaesthetic has been injected) and into the uterus to reach the frond-like projections of the placenta. It is essential that the operator avoids entering the amniotic or fluid sac around the baby. Placental cells are then sucked up into a syringe attached to the CVS needle, placed in culture fluid and sent to the lab.
The great advantages of CVS is that the test can be performed in the first trimester of pregnancy and results can be obtained speedily since the tissue is fresh and living and only needs a short time in culture. For some women this is a very important consideration. The disadvantage is that it may be associated with a higher risk of miscarriage, mosaic cell lines may confuse the results and abnormalities in the growth of the baby’s limbs have occasionally been reported.