A number of laboratory tests are suggested for all women early in their antenatal care. Some of these tests are performed on samples of blood and urine and some are actual analysis of cells from the cervix and vagina. In some instances a pregnant woman will be offered chorionic villus sampling.
Chorionic Villus Sampling
Chorionic villus sampling (CVS) is the removal of a small piece of placental tissue from the uterus during early pregnancy to screen the baby for genetic defects (Medline Plus). CVS is available to pregnant women, particularly those with a family history of inherited disorders, or for those women who are over the age of 35. It is an alternative test to amniocentesis and has the advantage that it can be done earlier than amniocentesis, from about ten weeks after fertilisation. The CVS test takes around twenty minutes to perform by an obstetrician. There are two different methods of performing this sampling.
Transcervical Chorionic Villus Sampling
Under continuous ultrasound scanning a fine catheter or fine forceps are passed into the vagina and are introduced into the cervix. Using this continuous ultrasound guidance a small amount of placental tissue is removed using suction or forceps.
Transabdominal Chorionic Villus Sampling
Using an ultrasound probe a needle is inserted through the wall of the abdomen into the uterus and then into the placenta. A small sample of placental tissue is then removed using a syringe attached to the end of the needle.
Which Fetal Disorders can be Detected?
- Down’s Syndroms
- Cystic Fibrosis
- Duchenne Muscular Dystrophy
- Sickle Cell Anaemia
- Turner Syndrome
Which Foetal Disorders Cannot be Detected?
- Spina Bifida
Are There any Risks Associated With Chorionic Villus Sampling?
CVS does carry a risk of miscarriage (when the pregnancy is lost in the fist 24 weeks). However, results can vary, with most estimates suggesting that CVS is slightly more dangerous than amniocentesis, which has a miscarriage risk of around one percent (Smith). Similarly, as with all types of surgical procedures, there is a risk of infection as a result of this procedure. Infection can occur if there are bacteria on your skin or on the surgical instruments that are being used.
What Precautions Should I Take Following Chorionic Villus Sampling?
- Minimise heavy lifting for about one week.
- Avoid strenuous exercise for 2-3 days.
- Avoid sexual intercourse for several days.
After receiving the results of any ante-natal test there will be ample opportunity to discuss the findings with the obstetrician and genetic counsellor. All health professionals will be aware that parents may have difficult decisions to make and a non-judgemental approach is cultivated in all aspects of the process.
Disclaimer: The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is concerned about his or her health should contact a doctor for advice.
Crespigny, L and Chervenak, F Prenatal Tests: The Facts. Oxford University Press.
National Health Service Choices. 1
Smith, H The Pregnancy Pocket Bible. PB Pocket Bibles