What Is Chorionic Villus Sampling (CVS)?

"How early can a test actually give us an answer?" It's often the first question parents ask when a screening result or a family history has raised a worry early in pregnancy. Chorionic villus sampling — CVS for short — exists because of that question. It's a diagnostic test done in the first part of pregnancy that examines a tiny sample from the placenta, and it can give definite information about certain chromosome and genetic conditions far earlier than most other tests.

The video at the top of this page introduces the test in just under five minutes. As it explains, CVS is a diagnostic test for identifying chromosome abnormalities and other inherited disorders, and it may be recommended when your or your partner's family medical history reveals a potential risk. What follows answers, one by one, the questions people usually ask next.

What exactly is being sampled — and why the placenta?

The chorionic villi are tiny, finger-like parts of the placenta, the organ that links you and your baby during pregnancy. They matter for testing because the placenta develops from the same fertilised egg as the baby, so its cells normally carry the same genetic make-up. A small sample of those villi can therefore be examined in the laboratory for the baby's chromosomes and genes without touching the baby itself. That's also why our pregnancy hub places CVS among the early diagnostic tests rather than the routine scans: it answers a genetic question, using placental tissue as the messenger.

Who is offered CVS, and when does it happen?

CVS is not part of every pregnancy. It's a test your care provider may raise if a screening result suggests a higher chance of a chromosome condition, if an ultrasound finding needs a firmer answer, or — as the video above puts it — if you or your partner has a family history that reveals a potential risk of an inherited disorder. The offer normally comes early, in the first trimester, which is precisely the point of the test: it can be done, and its results prepared, before the stage at which the alternative diagnostic test becomes possible. Knowing roughly where you are in the pregnancy matters for all of this timing, and our due date calculator is a handy way to check dates. Whether to have CVS at all is always your choice — it's an offer, not an obligation, and your team should explain the benefits and the limitations before you decide.

How is the sample actually taken?

There are two established routes, and both are guided by ultrasound from start to finish, so the person performing the test can watch the placenta and the baby on screen throughout. In the transabdominal route, a fine needle is passed through the abdomen into the placenta and a small sample is drawn out. In the transcervical route, a thin tube is passed through the cervix to reach the placenta instead. Which route is used depends on where the placenta is lying and on your team's judgement on the day. Ultrasound guidance is the quiet constant in either version — if you'd like to see how ultrasound is used in pregnancy more generally, the longer guide "How to use Ultrasound in Pregnancy" walks through what a scan shows and how the images are gathered, and our article on ultrasound in pregnancy covers the scans themselves. The sampling itself is brief, though the appointment around it — consent, scanning, and checking everything afterwards — takes longer.

How is CVS different from amniocentesis?

This is the comparison nearly everyone wants, because the two tests answer similar questions in different ways. CVS samples the placenta and can be done earlier in pregnancy. Amniocentesis samples the fluid around the baby, and it's performed later, once there's enough fluid to draw from safely. Both are diagnostic tests — they examine actual cells, rather than estimating a chance the way screening tests do — and both involve passing an instrument to reach the sample, so both carry a small procedure-related risk, which your team will discuss with you in the context of your own pregnancy. Our guide to amniocentesis and why it is done explains the fluid test in the same question-by-question way, and reading the two side by side gives a fair picture of the trade-off: earlier answers with CVS, a later test with amniocentesis.

What can CVS find — and what can't it find?

CVS is used to identify chromosome abnormalities — conditions that arise when a baby has extra, missing, or rearranged chromosome material — and specific inherited disorders, particularly where a family history means the laboratory knows what to look for. What it can't do is give a clean bill of health in every direction. It doesn't test for conditions that aren't chromosomal or genetic in that way; problems in how a structure develops, such as spina bifida, aren't detected by CVS and are looked for by other means, including later ultrasound scans. Results also take time — the sample has to be prepared and examined in the laboratory — and occasionally the placental cells give an unclear or mosaic picture that needs further testing to resolve. Your team will explain what your result does and doesn't cover, and what, if anything, happens next.

A word about the risks, kept in proportion. CVS is an invasive test, and like amniocentesis it carries a small risk of miscarriage, which is the main reason it's offered for a reason rather than routinely. Some cramping and light spotting afterwards are commonly described, and your team will tell you what they'd want you to phone about — heavier bleeding, leaking fluid, fever, or pain that isn't settling are the sorts of changes maternity teams generally want to hear about promptly. None of this is meant to steer you either way. It's the balance every parent offered CVS weighs: earlier, definite information about the conditions tested for, against a small risk from the procedure itself. There is no single right answer to that balance — there's only the answer that fits your situation, reached with a team that knows your history and your scans.

References & further reading

• NHS — Chorionic villus sampling: https://www.nhs.uk/tests-and-treatments/chorionic-villus-sampling-cvs/
• ACOG — Prenatal Genetic Diagnostic Tests: https://www.acog.org/womens-health/faqs/prenatal-genetic-diagnostic-tests
• Johns Hopkins Medicine — Chorionic Villus Sampling (CVS): https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/chorionic-villus-sampling-cvs
• MedlinePlus — Prenatal Testing: https://medlineplus.gov/prenataltesting.html

Frequently Asked Questions

Is CVS a screening test or a diagnostic test?

It's diagnostic. Screening tests estimate the chance of a condition; CVS examines actual placental cells in the laboratory, so it can give a definite answer about the chromosome and genetic conditions it tests for. That certainty is why it's offered when a screening result or family history has already raised a question.

Does CVS hurt?

Most people describe discomfort and cramping rather than sharp pain, and experiences vary with the route used. Your team will explain what to expect on the day, what they use to keep you comfortable, and what cramping or spotting afterwards is usual — and which symptoms should prompt a phone call instead.

How long do CVS results take?

The sample has to be prepared and examined in a laboratory, so results take time — sometimes an initial result comes sooner and a fuller result follows. Your team will tell you how results are given in your service and roughly when to expect them, so you're not left guessing during the wait.

If CVS is normal, does that mean the baby is definitely healthy?

Not in every direction. A normal CVS result is reassuring about the chromosome and genetic conditions tested for, but CVS doesn't detect every condition — structural problems such as spina bifida, for example, are looked for by other means, including later scans. Your team will explain what your particular result covers.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about chorionic villus sampling (CVS), not medical advice and not a diagnosis. Whether CVS is right for you is a decision for your own maternity and genetics team, who know your history, your screening results and your scans.