The short answer
CVS is usually done between about 10 and 13 weeks and takes a sample of placenta. Amniocentesis is usually done from 15 weeks and takes a sample of the fluid around the baby. Both carry a small risk of miscarriage, and both can be used for chromosome tests or for a focused test for a condition in the family. CVS gives you the answer sooner; amniocentesis can sometimes give a clearer answer about the baby, because a finding limited to the placenta will not confuse it.
The comparison
| CVS | Amniocentesis | |
|---|---|---|
| Usual timing | About 10–13 weeks | From about 15 weeks |
| What is sampled | A small piece of placenta | Fluid from around the baby, containing its cells |
| Main advantage | An answer weeks earlier | Not confused by a chromosome difference confined to the placenta |
| Main limitation | A placenta-only finding can complicate the result | The later timing means a longer wait |
| How it is done | Through the abdomen or through the cervix, depending on where the placenta lies | Usually through the abdomen |
| Miscarriage risk | Small | Small |
The procedure only collects cells. What can be diagnosed depends entirely on which laboratory test is ordered on them.
Why someone might choose CVS
It can give a diagnostic answer in the first trimester. That earlier timing can matter when:
- an NIPT result or a first-trimester scan is worrying;
- both parents carry changes for a serious recessive condition;
- one parent has a dominant or X-linked condition;
- the family’s exact gene change is already known and can be tested for;
- having the answer sooner would change how you prepare, or what you decide.
Why someone might choose amniocentesis
It may be preferred when the result needs to reflect the baby more directly than a piece of placenta can — particularly after certain NIPT findings.
It is also the only diagnostic option if the concern appears after the CVS window has closed.
The fluid can be used for chromosome analysis, a microarray, focused gene testing and, in some situations, tests relating to infection or spina bifida. What is appropriate depends on why the procedure is being done.
The placenta question, explained
The placenta and the baby usually have identical chromosomes. Occasionally they do not: a chromosome change can be present in placental cells and absent from the baby.
Because both NIPT and CVS look at placental material, that possibility affects which test is recommended after certain high-risk NIPT results.
A CVS result can itself show a mixed picture that needs an amniocentesis to sort out. That does not make CVS a screening test — it is a known limitation of that particular sample.
Why the miscarriage numbers you find differ
You will see different figures from perfectly reputable sources, because they are not all measuring the same thing:
- some count every miscarriage that happens after the procedure;
- others try to estimate only the extra losses caused by the procedure itself, above the risk the pregnancy already had.
Timing, who is being tested, twins and the experience of the operator all change the number too.
So ask the service:
- Is this the total risk, or the extra risk from the procedure?
- Is it for a single baby or for twins?
- Is it based on this centre’s own recent results?
- Is there anything about me that changes it?
That conversation is far more useful than comparing two percentages from two different websites.
Decide which uncertainty you mind most
CVS shortens the wait but can leave a placenta-versus-baby question in a small number of cases. Amniocentesis removes that particular question but means waiting longer. Either one can still produce an unexpected or uncertain finding.
Before choosing, confirm what condition is being tested for, which laboratory test will be run, when the early and final results should arrive, and what would happen next if a result came back unclear.
Sources and further reading
Common questions
- Which is safer, CVS or amniocentesis?
- Both carry a small risk when done by an experienced team, and published figures vary. Ask the centre doing the procedure for its own current number rather than assuming a single universal figure.
- Is CVS as accurate as amniocentesis?
- Both give diagnostic answers, but CVS tests placenta. Occasionally the placenta's chromosomes differ from the baby's, and an amniocentesis is then needed to clarify.
- Can CVS test for spina bifida?
- No. CVS cannot measure the amniotic fluid markers used for open neural tube defects, so ultrasound and second-trimester screening still matter.
- How quickly do results come back?
- Some chromosome results come back within a few days. Fuller chromosome analysis, a microarray or a focused gene test can take longer. Ask exactly which tests were ordered and when each result is expected.