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Health Matters

PrenatalDiagnosis: ChorionicVillusSampling

Mariana Torgal (Obstetrician-Gynecologist) . 06/11/2015

Chorionic Villus Sampling (CVS) is an invasive prenatal diagnosis technique where a small sample of placenta tissue is collected (villus chorionic). This sample is then used to evaluate the foetus genetic material.

Since foetus and placenta come from the exact same cell, they share the same genetic material, few exceptions excluded. For most cases, CVS is performed in order to evaluate foetal karyotype and identifychromosome changes like 21, 13 and 18 trisomies.  In rare cases, the aim of CVS may be the study of some specific genes.

  • When and how is CVS performed?

CVS is performed between 11 and 14 weeks of pregnancy. It is an outpatient procedure.

It may be performed through the abdomen or trans-vaginally. This decision is up to the consultant and is related to the location of the placenta. In both cases, it is an ultrasound-guided biopsy.

Abdominal CVS starts with a small injection to administer local anaesthesia in the skin. Afterwards, a thin needle is inserted and, guided by an ultrasound, crosses the uterine wall and reaches the placenta. The villus chorionic (placenta) sample is then suctioned with the help of a syringe and sent to the lab.

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For the transvaginal CVS the patient is in Lithotomy position and a speculum is placed for cervical observation (similar to a gynaecologic routine examination). The practitioner introduces a biopsy tweezers in the external os of the cervix and, guided by an ultrasound, reaches placenta tissue and performs the biopsy.

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CVS is not considered a painful procedure, however it may cause some pelvic discomfort.

On the day of the exam, a blood sample should be collected as well, in order to rule out maternal cell contamination.

Pregnant women with Rh negative blood type should be given an intramuscular injection of Anti-D (Rho) Immunoglobulin for Rh-prophylaxis, up to 72 hours after procedure.

As with any other invasive technique, CVS cannot be performed without a written consent from the patient.

  • In what situations is CVS recommended?

The most common indications for CVS procedure are:

  • First trimester combined screening with increased risk of aneuploidies

  • Foetal anomaly detected by ultrasound

  • Chromosomal or Genetic Disorder in previous pregnancy

  • Family history of genetic disease with risk of foetal transmission

  • Biochemical or molecular study enabled by a placenta sample

  • Option of the patient, dully informed of associated risks

  • What are the associated risks of CVS?

The main associated risk is foetal loss (miscarriage), which occurs in 1% of procedures and is similar to the risk of miscarriage after an amniocentesis procedure. Risk of infection is 1/500. There is a slightly increased risk of premature rupture of membranes.

In about 1% of procedures, CVS results may be inconclusive, either due to insufficient collection or maternal cell contamination.

  • CVS procedureinstructions

Prior to exam, eat as usual, since there are no special diet indications for this procedure.

After the procedure, women should go home to rest. Most women will be able to resume their physical activity within 24h or, at most, 48h. Sexual abstinence is recommended in the first days after procedure.

At Joaquim Chaves Saúde this technique is available since 2014 and we have internally developed our own methodologies in processing these samples. Learn more here.

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