Chorionic Villus Sampling (CVS)
Chorionic Villus Sampling (CVS) is a diagnostic test performed at Melbourne Ultrasound for Women, involving the extraction of a small tissue sample known as "chorionic villi" from the developing placenta of expectant mothers.
The placenta typically shares genetic characteristics with the fetus, allowing for the detection of chromosomal or DNA abnormalities like Down syndrome.
At Melbourne Ultrasound for Women, our dedicated specialized Obstetrician Gynaecologist possesses extensive expertise in administering CVS for pregnant individuals.
Who is offered a CVS?
Most CVS testing is recommended for pregnant women with specific risks of chromosomal abnormalities, such as Down syndrome. This may encompass:
Women who have exhibited an elevated probability of a chromosome-related condition through cell-free fetal DNA testing (NIPT).
Women who have displayed an elevated likelihood on a nuchal translucency test.
Women aged 35 and older.
Women who have previously experienced a pregnancy affected by a chromosomal abnormality.
Parents known to carry a chromosomal abnormality themselves.
Parents known to be carriers of genetic disorders.
Parents at risk of having a baby with one or multiple rare "metabolic" disorders.
In some instances, CVS might be conducted for women particularly concerned about the risk of chromosomal abnormalities.
Trans-abdominal CVS
The sampling process entails utilizing a needle inserted through the abdominal wall, known as trans-abdominal CVS. A delicate needle is guided through the skin and into the uterus to the placental edge, its trajectory meticulously monitored on the ultrasound display. A finer needle is subsequently introduced through the outer needle and into the placental tissue.
Using a syringe, minute fragments of placental tissue are drawn up for extraction. The obtained tissue is evaluated to ensure its adequacy, and if necessary, additional aspirations are carried out through the inner needle without causing any extra discomfort. It is important to note that the needle is never introduced into the amniotic sac at any point during the procedure, which serves to minimize test-related risks, and any fetal movements that occur during the procedure are not a cause for concern.
How is CVS performed?
Trans-cervical CVS
Should your scan reveal that the placenta is developing at the rear uterine wall and positioned low in the uterus, it might facilitate your obstetrician in conducting the CVS procedure trans-cervically, where a speculum is introduced into the vagina and the cervix is cleansed with an antiseptic solution; subsequently, a specialized catheter is carefully navigated into the placenta aided by ultrasound, allowing for the gentle aspiration of placental tissue.
Usually this trans-cervical CVS procedure is entirely painless, and a minor amount of bleeding is relatively frequent; the accompanying image illustrates the catheter's passage through the cervix and into the placenta situated on the back wall of the uterus.
When is CVS carried out?
Ideally, the CVS test is recommended during the 11-13 week gestation period. However, it can be performed as early as 10 weeks and up to 40 weeks if necessary.
Preparation Guidelines for Your Appointment
Having knowledge of your blood group, especially your Rhesus (Rh) status, is vital prior to an Amniocentesis test. If possible, kindly request this information from your referring doctor or bring your blood group card to your Melbourne Ultrasound for Women appointment
Please be aware, if you possess a Rhesus negative blood group, you will need an anti-D injection after the CVS.
Our proficient Melbourne Ultrasound for Women Obstetrician will provide you with comprehensive information about this during your Amniocentesis appointment.
When you come in for your CVS appointment at Melbourne Ultrasound for Women, having a moderately full bladder is beneficial.
This positioning elevates the uterus into the abdominal cavity, simplifying access to the placenta for the procedure. If, however, you find the full bladder uncomfortable, our skilled team will guide you to partially empty your bladder if needed.
What is done with the cells?
The cells obtained at CVS are sent to Victorian Clinical Genetic Services (VCGS) and are allowed to grow in the laboratory until there are enough for testing the chromosomes.
Each of the chromosomes is carefully examined to check that there are the correct number and that the appearance and length of each chromosome is normal. If the fetus has Down Syndrome then there is an additional chromosome 21 present. The sex of the fetus can also be determined by looking at the chromosomes - you can find this out if you ask your doctor.
The laboratory will usually have the result available within 2 weeks. Your doctor will be informed and he or she will pass it on to you. If you wish, an extra test, called FISH, can be carried out to tell you within 2 working days if Down Syndrome is present. The laboratory charges extra for FISH testing.
Understanding test risks
A study encompassing Victor Hurley's patients indicated that the miscarriage risk attributed to CVS itself is 1 in 100 or lower. (It's important to note that a natural miscarriage rate of about 1 in 50 after 10 weeks is present regardless of CVS.)
Patients frequently inquire about the timing of potential miscarriages following CVS. This question poses complexity, primarily because most post-CVS miscarriages are "natural" and unrelated to the test. However, if no complications arise within three weeks post-test, it's unlikely that any ensuing issues stem from the procedure. The likelihood of complications is significantly linked to the operator's skill and experience.
As of our current testing stage, i.e., at 10 weeks or later, there's no evidence suggesting that CVS causes fetal defects, including limb abnormalities. Rare complications may encompass bleeding, infection, and ruptured membranes.
Instances of complications to the pregnant woman herself are extremely uncommon. If you possess an Rh negative blood group, it's advisable to receive anti-D treatment post-CVS. Nevertheless, if your doctor has indicated the presence of antibodies, amniocentesis might be preferred.
It's noteworthy that, akin to any test, CVS may encounter failures due to inadequate sample collection or laboratory result production difficulties. Both of these risks are exceptionally infrequent.
While exceedingly rare, the possibility of inaccurate results exists. In roughly 1% of cases, uncertain outcomes arise, potentially necessitating further testing (typically amniocentesis) to clarify the situation.
Post Amniocentesis care guidelines
After undergoing the CVS test, it's advisable to prioritize rest for the remainder of the day. It's common for women to feel a sense of tiredness and heightened emotions, alongside some mild belly soreness. While it's not necessary to stay in bed, we recommend avoiding strenuous activities such as lifting heavy weights. Should you feel well enough to resume work, that's acceptable.
The majority of women might experience brief episodes of mild crampy period-like pains, lower abdominal discomfort, or even leg pains post-CVS. This discomfort is most likely to manifest once the effects of the local anesthetic have diminished, typically within the initial half hour following the test. Occasionally, some women might notice minor vaginal blood spotting, which is also considered normal due to the placental biopsy.
We will ensure a 10-15 minute recovery period following your CVS procedure. Additionally, we will provide you with a comprehensive list of post-procedure considerations to keep in mind. It's important to remember that a minor degree of spotting is relatively common, given that we've conducted a placental biopsy.
Furthermore, many individuals find it reassuring to have a companion available to drive them home after CVS. While resting for the remainder of the day is recommended, there's no requirement to stay in bed. Your daily routine can continue without limitations beyond this point.
Subsequent to the CVS, a subset of women might encounter lower abdominal discomfort or period-like pains, occasionally accompanied by momentary feelings of faintness. It's crucial to note that these symptoms do not pose any risk to the pregnancy. Notably, instances of bleeding following transabdominal CVS are highly uncommon.
When are you informed of the CVS results?
Dr Hurley will ring you with the Amniocentesis results as soon as they become available, and we also forward them to your referring doctor.
Fast FISH results are available in 24-48 hours. The full karyotype usually takes 10-14 days; microarrays usually take 5-10 days, and our team will call with all of your results whether they are normal or not.
