Chorionic Villous Sampling (CVS)
CVS is a prenatal diagnostic procedure where fetal cells from the amniotic fluid are obtained and used to determine whether a fetus’ chromosomes are normal or whether there is a chromosome abnormality present.
CVS are tests carried out during pregnancy most commonly to check your baby for disorders such as Down syndrome and, where appropriate, rarer specific inherited disorders.
CVS involves taking a tiny amount of the developing placenta, where it is attached to the uterus. The placenta contains tissue that is genetically identical to your baby. CVS is performed most commonly between 11 and 14 weeks.
Who is offered this test?
CVS is offered to patients who are:
high risk for chromosome abnormalities.
A high risk Combined First Trimester Screen
NIPS test has indicated a “high risk” result
There has been a previous pregnancy with a chromosomal abnormality or other genetic disorder
There is a known inherited genetic disorder in the family of either the mother or father of the fetus for example cystic fibrosis, thalassaemia or sickle cell disease.
How is a transabdominal CVS performed?
Your skin is cleaned in the area where the needle will be inserted. The Obstetrician will use some local anaesthetic to numb the skin. Using an ultrasound probe to guide the direction, a fine needle is pushed through the abdomen and the wall of the womb into the placenta. A tiny amount of placental tissue is sucked up into a syringe. The needle is then taken out and your baby is observed for a short time on ultrasound.
The sample will be checked to ensure an adequate sample has been taken for the laboratory to be able to process the results.
What are the risks of a CVS?
Every pregnancy carries a risk of miscarriage. CVS involves putting a needle through the wall of the womb, there is a small additional risk of a miscarriage due to injury or infection in the womb.
The additional overall risk of miscarriage from CVS is 1:500 (0.2%).
You may notice some ‘spotting' of blood and cramping for a few hours afterwards. This is normal and it is safe to take paracetamol. If you experience any unusual symptoms immediately after the test, such as feeling shivery (as if you have flu), fluid loss, bleeding or contractions, then you should seek advice immediately.
Two sets of results will be available:
the short term result is usually available within 1-2 days which examines the 5 most common abnormal chromosomes including Down Syndrome.
The long term result takes around 14 days and looks at all chromosomes in greater detail.
One of our Doctors at Wellington Ultrasound or your referring Doctor will discuss the short term results with you over the phone within 2-3 days of you having the test. You will be asked if you would like to know the sex of your baby as this may also be determined from the chromosomes.
The long term results will be discussed with you by your Doctor, over the phone with one of our Doctors or at your next appointment with us. If the result is abnormal our Specialists are here to help, providing further information and counselling.
Results of CVS are very accurate but occasionally the results can be very difficult to interpret. In such circumstances further chromosome testing may be required.
Care following a CVS
Some women have mild cramping and a small amount of vaginal loss, either bleeding and/or amniotic fluid, after the procedure. This usually resolves without treatment over 24 to 48 hours. If it persists or is heavy, please seek medical advice.
It is recommended women avoid strenuous activities and sexual intercourse for 48 hours following a CVS.
Paracetamol is safe to take in pregnancy and may be required following the procedure.
If your blood group is Rh (sometimes called rhesus) negative, you will be recommended an injection of anti-D immunoglobulin after the procedure to prevent you from developing antibodies against the baby’s blood cells.