Chorionic villus sampling (CVS)

 

  1. This procedure is usually performed from 11 weeks, routinely between 11 and 13 weeks gestation*. It should not be performed prior to 10 weeks gestation due to the risk of limb defects.
  2. A sample of chorionic villus (pre-placental tissue) is removed by a fine needle, either transabdominally, or less frequently transvaginally, under ultrasound guidance (see Figure 6).
  3. The tissue is used for chromosome analysis, and in some specific situations, may be used for diagnosis (DNA or biochemical analysis) of a genetic condition where there is a family history.
  4. It is a procedure that can be performed earlier in pregnancy than amniocentesis, and has the benefits of an early scan that may detect anencephaly.
  5. Some women experience cramping and, occasionally, vaginal bleeding after CVS.
  6. The miscarriage rate, in experienced hands, is estimated at ~1% above the background risk.

 

* In South Australia CVS is sometimes performed between 10 and 11 weeks

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Important points about CVS

  1. CVS has a 1% risk of equivocal results. This includes the risk of placental mosaicism – the presence of a mixture of cells with normal and abnormal karyotype, or maternal cell contamination of the sample. In this case, amniocentesis may be necessary to clarify the karyotype of the fetus.
  2. CVS has a 0.1% rate of failure to detect a pregnancy with a chromosomal anomaly, due to the occasions when there is an abnormal karyotype in the baby, but not in the placenta.
  3. CVS may not detect fetal chromosomal mosaicism.
  4. Test results take about one week.
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Figure 6

CVS procedure

Figure 6

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