CVS (Chorionic Villus Sampling): Complete Guide
Chorionic villus sampling (CVS) is a diagnostic test that can identify chromosomal and genetic conditions earlier in pregnancy than amniocentesis. It's usually offered after a screening test (like the combined test) has shown a higher chance of a condition such as Down's, Edwards', or Patau's syndrome. Here's what the procedure involves and what to expect.
What CVS Involves
CVS takes a small sample of cells from the placenta — specifically the chorionic villi, tiny finger-like projections that share the baby's genetic makeup. It's carried out under ultrasound guidance, either:
- Through the abdomen (transabdominal) — a fine needle is passed through the tummy, the most common approach
- Through the cervix (transcervical) — a thin tube is passed through the cervix, used in some cases depending on the position of the placenta
The procedure itself typically takes around 10 minutes, though you may be at the clinic for longer including preparation and monitoring afterwards. Most women describe it as uncomfortable rather than acutely painful, similar to period cramping.
When CVS Is Done
CVS is usually carried out between 11 and 14 weeks of pregnancy, making it available earlier than amniocentesis, which is typically done from 15 weeks onwards. This earlier timing is one of the main reasons some parents choose CVS over waiting for amniocentesis, as it allows decisions to be made sooner if a condition is found.
Accuracy and Limitations
CVS is a highly reliable diagnostic test for chromosomal conditions, giving a definitive answer rather than the "chance" figure a screening test provides. It isn't infallible, though — in a small number of cases, results can be affected by a phenomenon called confined placental mosaicism, where the placenta's cells differ slightly from the baby's, which occasionally requires a follow-up test to clarify. Importantly, CVS cannot detect neural tube defects like spina bifida, since it doesn't sample amniotic fluid — this is checked separately, usually via your anomaly scan.
Risks to Consider
The main risk with CVS is a small increase in miscarriage chance compared with not having the test, generally estimated as modestly higher than the risk linked to amniocentesis. Your fetal medicine specialist will talk through the specific risk for your situation before you decide, and it's entirely your choice whether to go ahead with a diagnostic test after a screening result.
Getting Your Results
Rapid results for the most common conditions are sometimes available within days, with full results typically taking around 2-3 weeks. A genetic counsellor or specialist midwife is usually available to talk through what any result means for you and your pregnancy.
Frequently Asked Questions
Which is better: CVS or amniocentesis?
Neither is universally "better" — CVS can be done earlier (11-14 weeks vs. 15 weeks onwards for amniocentesis) but carries a slightly higher miscarriage risk, while amniocentesis can also detect neural tube defects, which CVS cannot. Your obstetric or fetal medicine team will help you weigh timing, risk, and what each test can and can't tell you, based on your individual circumstances.
How is CVS performed?
CVS is performed under ultrasound guidance, using either a fine needle through the abdomen or a thin tube through the cervix to take a small sample of placental tissue. The procedure takes around 10 minutes and is generally described as uncomfortable rather than severely painful, similar to strong period cramps.
Is CVS painful or risky?
Most women find CVS uncomfortable rather than very painful, and any cramping or spotting afterwards is usually mild and short-lived. The main risk to be aware of is a small increase in miscarriage chance associated with the procedure, which your care team will discuss with you individually so you can make an informed decision.
This article is for informational purposes only and does not constitute medical advice.
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