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CVS and amniocentesis: what each test involves | CION Cancer Clinics
CVS and amniocentesis are the two tests that can check a pregnancy for a family's known cancer gene fault. CVS samples the placenta earlier in pregnancy; amniocentesis samples the fluid around the baby a few weeks later. This page explains what happens at each, the small risk they carry, and what the answer can and cannot tell you. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- What are CVS and amniocentesis, and why would a carrier be offered one?
- How CVS and amniocentesis differ
- What actually happens at the appointment
- CVS or amniocentesis: which fits your situation?
- What this page cannot tell you
- Four things couples worry about, and what is actually true
- Common questions about CVS and amniocentesis
The short answer
What are CVS and amniocentesis, and why would a carrier be offered one?
Both are tests that take a small sample from a pregnancy so the baby's genes can be checked. CVS takes a few cells from the placenta, earlier in pregnancy. Amniocentesis takes a little of the fluid around the baby, a few weeks later. When a parent carries a known cancer gene fault, either sample can show whether the baby has inherited that exact fault.
Why this is different from routine pregnancy scans
Scans and screening blood tests look for signs that something might be wrong. They cannot read a single gene. CVS and amniocentesis are diagnostic. They give a clear yes or no for the fault your family is known to carry, as long as the laboratory has a test ready for it.
The step that has to come first
The lab needs to know exactly which change it is looking for. That means the carrier's genetic report, and sometimes a blood sample from one or both parents, before the pregnancy test can be designed. Talk to your genetic counsellor before you conceive, or as early in pregnancy as you can, so there is time to set this up.
Choosing to have CVS or amniocentesis does not commit you to any particular decision about the result.The two tests
How CVS and amniocentesis differ
The main difference is timing. Which one you are offered depends on how far along the pregnancy is and what your centre provides.
Chorionic villus sampling (CVS)
A thin needle is passed through the tummy, guided by ultrasound, to take a tiny piece of the placenta. Less often, the sample is taken through the neck of the womb instead.
Key points
- Usually done between the eleventh and fourteenth weeks
- Gives an answer earlier in pregnancy
- The test itself takes about ten minutes
Amniocentesis
A thin needle is passed through the tummy into the womb, again guided by ultrasound, to draw off a small amount of the fluid that surrounds the baby. That fluid contains the baby's own cells.
Key points
- Usually done between the fifteenth and twentieth weeks
- Can be done later if needed
- The test itself takes about ten minutes
The risk both share
Each carries a small added chance of miscarriage. NHS guidance puts it at around one in every two hundred pregnancies for amniocentesis, and below that for most pregnancies having CVS. Your fetal medicine doctor will explain the figure for your own pregnancy.
What neither test will tell you
They answer whether the baby carries the family's fault. They cannot say whether that child will ever develop cancer, or when. Under Indian law, neither test will ever be used to reveal the baby's sex.
Not sure whether this applies to you?
Ask an oncologistOn the day
What actually happens at the appointment
A scan and a conversation
The doctor checks the baby's position and the placenta on ultrasound, confirms the family's fault is what will be tested, and takes your written consent. Bring the carrier's genetic report.
The sample
The skin is cleaned and a thin needle is guided in under ultrasound. Many women describe pressure or a sharp sting rather than severe pain. A local anaesthetic is sometimes used.
A blood test for the mother
The lab often asks for a sample of your blood too, to check that the result reflects the baby's cells and not your own. If your blood group is rhesus negative, you will be offered an injection to protect the baby.
Rest and going home
You can usually go home the same day. Take things gently for the rest of the day, and expect some period-like cramps for a few hours. Have someone else drive you if you can.
Side by side
CVS or amniocentesis: which fits your situation?
CVS
Amniocentesis
Earlier in pregnancy, so decisions can be made sooner
Later in pregnancy, which some couples find harder
Samples the placenta, which very rarely differs from the baby
Samples cells shed by the baby into the fluid
Needs a fetal medicine specialist with CVS experience
More widely available in larger hospitals
Useful if you want the answer within the first trimester
An option if the pregnancy was confirmed late
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After the test: when not to wait
Contact your maternity unit or go to the nearest hospital the same day if you have vaginal bleeding, fluid leaking from the vagina, a fever or shivering, tummy pain that paracetamol does not ease, or cramping pain that comes and goes like contractions. Say that you had CVS or amniocentesis and when. Do not wait until your next appointment.
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Being straight with you
What this page cannot tell you
It cannot tell you whether testing your pregnancy is right for you. That choice rests on your beliefs, your family's experience of the cancer, and what you would do with the answer. A genetic counsellor can help you think it through before you book anything. What your specific variant means is a question for the counsellor who ordered the carrier's test.
It cannot tell you what a centre will offer
Not every fetal medicine unit will test a pregnancy for a gene that raises cancer risk in adult life. Some will; some will ask for a discussion first. What happens after a result is also governed by Indian law. Ask these questions before you are pregnant, not after, and read our page on the PCPNDT Act.
Who this does not apply to
Most pregnant women never need either test for a cancer gene. They are only relevant when a parent carries a confirmed fault. A variant of uncertain significance, a change whose meaning is not yet known, is not tested for in pregnancy. A fault found only inside a tumour cannot pass to a child; that testing belongs to targeted therapy.
Commonly believed
Four things couples worry about, and what is actually true
"The needle goes into the baby."
It does not. Ultrasound is used throughout so the doctor can see the baby and keep the needle well away. The sample comes from the placenta or from the fluid around the baby.
"If we have the test, we have already decided to end the pregnancy."
Many couples test simply to know, so they can plan and prepare. The result gives you information. What you do with it remains your decision, and there is no wrong answer.
"A normal scan means the baby does not have the gene."
A scan cannot see a gene fault. A baby carrying an inherited cancer gene looks and grows exactly like any other baby. Only a genetic test on a sample can answer the question.
"The test will also tell us if it is a boy or a girl."
It will not. Revealing the sex of a baby before birth is illegal in India under the PCPNDT Act. Genetic tests on a pregnancy report only the condition they were ordered for.
Questions we are asked
Common questions about CVS and amniocentesis
Does CVS or amniocentesis hurt?
Most women describe it as uncomfortable rather than painful, similar to a blood test or a period cramp. Some feel a sharp sting as the needle goes in, then pressure. Cramps for a few hours afterwards are common and usually settle with rest.
How soon will we get the result?
It depends on the laboratory. Quick chromosome results can come within days, but a test for one family's specific gene fault usually takes longer, often a couple of weeks or more. Ask the unit for its expected timing before the procedure.
Can the test be wrong?
Errors are uncommon. Occasionally the placenta carries a different genetic pattern from the baby, or the sample contains some of the mother's cells. When there is doubt, the lab may recommend a repeat test, often amniocentesis after CVS.
Does it matter which parent carries the fault?
The test itself is the same either way. If the mother is the carrier, her blood sample helps the lab make sure it is reading the baby's genes and not hers. Both parents' reports should be brought to the appointment.
Where in Telangana can CVS or amniocentesis be done?
Both are done in fetal medicine units, which are mostly in larger hospitals in Hyderabad. They must be registered under the PCPNDT Act. Families in the districts usually travel once for the procedure. Your genetic counsellor can suggest a unit and send the family's report ahead.
Can I continue working afterwards?
Most women rest for the rest of that day and return to desk work the next day. Avoid heavy lifting or strenuous activity for a short while. Your doctor will give you specific advice depending on how the procedure went.
Is there a test without any miscarriage risk?
Testing embryos before pregnancy through IVF avoids a procedure during pregnancy, though it brings its own costs and demands. Blood tests on the mother that read the baby's DNA exist for some conditions, but are not yet routine for a family's cancer gene in India.
What happens if the baby has inherited the fault?
A genetic counsellor will talk you through the result and every option, without pressure. Many couples continue the pregnancy, knowing the child can be told as an adult and watched closely from then on. Whatever you decide, support is available.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- NHS — Chorionic villus sampling
- NHS — Amniocentesis
- MedlinePlus — Chorionic villus sampling
- MedlinePlus — Prenatal Testing
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Prenatal diagnosis for a known family variantHow testing a pregnancy fits into the bigger pictureThe PCPNDT Act and what it restrictsWhat Indian law allows during pregnancy testingDeciding not to test the pregnancyWhy many couples choose not to, and that is finePGT-M explainedTesting embryos before a pregnancy begins
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Thinking about testing a pregnancy for a family gene?
A genetic counsellor can check whether a test can be set up for your family's fault and explain the options before you decide. One helpline serves every CION centre.