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CVS and amniocentesis: timing, risks and what to expect | CION Cancer Clinics
CVS is usually done between the 11th and 14th week of pregnancy, and amniocentesis from the 15th week onwards. Both take a sample carrying the baby's genes, so a lab can check for thalassaemia major or sickle cell disease when both parents are carriers. CVS gives an earlier answer. Amniocentesis suits couples who find out later. Both carry a small risk of miscarriage. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- When are CVS and amniocentesis done for thalassaemia?
- How do CVS and amniocentesis differ?
- What happens during the procedure?
- Which test fits where you are right now?
- What do families often believe about these tests?
- What happens after the sample, and what can it not tell you?
- Common questions about CVS and amniocentesis
The short answer
When are CVS and amniocentesis done for thalassaemia?
CVS is usually done between the 11th and 14th week of pregnancy. Amniocentesis is usually done from the 15th week onwards. Both collect a sample that carries the baby's genes, so a lab can check whether the baby has inherited thalassaemia major or sickle cell disease.
Why the earlier test is often preferred
CVS gives you an answer earlier in the pregnancy. That leaves more time to think, to talk as a family, and to repeat a test if the first sample does not give a clear answer. If you do decide to end an affected pregnancy, doing so earlier is usually simpler for the mother's body.
Why amniocentesis still matters
Not every couple learns they are both carriers in time for CVS. Many find out at the first antenatal visit, or when the second partner's report finally comes back. For them, amniocentesis is the route that is still open. It answers the same question, only later.
What decides the timing for you
Three things matter most: how far along the pregnancy is today, whether both parents' exact gene changes are already known, and how quickly a foetal medicine centre can see you. The DNA work on both parents often takes longer than the procedure itself, so start it at once.
This page explains the two procedures. It cannot tell you which one suits your pregnancy. Your obstetrician decides that with you.Side by side
How do CVS and amniocentesis differ?
CVS (chorionic villus sampling)
Amniocentesis
Takes a tiny piece of the placenta, the organ that feeds the baby
Takes a small amount of the fluid around the baby
Usually between the 11th and 14th week
Usually from the 15th week onwards
Needle through the tummy, or sometimes through the vagina
Needle through the tummy only
Answer comes earlier in the pregnancy
Answer comes later, with less time to decide
A small chance of miscarriage
A small chance of miscarriage, broadly similar
Not sure whether this applies to you?
Ask an oncologistOn the day
What happens during the procedure?
Before you go in
Bring both partners' carrier reports and any DNA reports. The doctor explains the procedure, the small risk and what the lab will look for. You sign a consent form. Ask any question you have now.
The scan
An ultrasound scan checks how far along the pregnancy is, where the placenta lies and how the baby is lying. This scan decides where the needle goes, and sometimes whether it is safe to go ahead today.
The sample
The skin is cleaned and often numbed. A thin needle is guided in while the doctor watches the screen. It takes only a few minutes. Most women describe pressure or a cramp rather than sharp pain.
Resting and going home
You rest for a short while, and the baby's heartbeat is often checked again. Most women go home the same day. Plan to take the rest of the day easy, and bring someone with you for the journey.
Your situation
Which test fits where you are right now?
These are common situations, not rules. Your obstetrician and the foetal medicine team make the final call with you.
Planning a pregnancy
This is the easiest place to be. Both of you can finish carrier and DNA tests before you conceive, so CVS can be booked early.
Worth asking about
- Testing embryos through IVF
- Which centre will do CVS
Early in pregnancy
If you have only just found out you are pregnant and both of you are carriers, CVS is usually still possible. The race is to get the parents' DNA results in time. Ask for this to be done urgently.
Past the CVS window
Amniocentesis is the usual choice. The result comes later, so talk through your options with your family before the procedure, not only after the result.
In a few cases a sample of the baby's cord blood is taken later still. Ask whether it applies to you.Who these tests do not suit
If only one partner is a carrier, a procedure is rarely needed. If the placenta sits in an awkward spot, one route may be ruled out. Some couples simply choose not to test, and that is their right.
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Commonly believed
What do families often believe about these tests?
"We can wait for the big scan later in pregnancy. It will show if something is wrong."
An ultrasound scan cannot show thalassaemia or sickle cell disease. These are problems in the blood, not in the shape of the baby. Only a DNA test on a sample can answer the question.
"Amniocentesis is safer, so we should wait for it."
In experienced hands the risk of the two procedures is broadly similar. Waiting mostly costs you time. Ask the doctor about the risk in their own practice rather than choosing by reputation.
"The needle goes into the baby."
It does not. The needle goes into the placenta for CVS, or into the fluid for amniocentesis. The doctor watches on the ultrasound screen the whole time to keep it away from the baby.
"Once the sample is taken, the result will surely be clear."
Usually it is. Occasionally the sample is too small, or mixed with the mother's cells, and the lab cannot give a firm answer. This is one more reason to test early, while a repeat is still possible.
Did you know
In India, telling parents the sex of the baby before birth is against the law. A CVS or amniocentesis done for thalassaemia or sickle cell looks only for the blood disorder, and the report will not say whether the baby is a boy or a girl.
After the procedure
What happens after the sample, and what can it not tell you?
After CVS or amniocentesis, most women feel mild cramping or notice a little spotting for a short while. Take it easy for the rest of the day. Contact the centre or go to the nearest emergency department at once if you have heavy bleeding, fluid leaking, a fever, chills or strong, worsening pain.
Waiting for the result
The lab compares the baby's genes with both parents' gene changes. How long this takes depends on the lab and on whether the parents' DNA work was already done. Ask on the day who will call you and who will explain the result in person.
What the result cannot tell you
The report says whether the baby is affected, a carrier or unaffected. It cannot say exactly how mild or severe the condition will be for a child who is affected. That depends on more than one gene, and on care after birth.
Where CION fits in
CION does not perform CVS or amniocentesis. Our haematology team can read both partners' reports with you, explain what they mean together, and help you reach a qualified foetal medicine centre quickly. If the baby is affected, we can explain what life with the condition involves.
Questions we are asked
Common questions about CVS and amniocentesis
I just found out we are both carriers. Is it too late for CVS?
Not always. It depends on how far along you are and how fast both parents' DNA tests can be done. Call your obstetrician today, not at your next routine visit, and ask for an urgent referral to a foetal medicine centre. If CVS is no longer possible, amniocentesis usually still is.
What is the risk of miscarriage?
For both procedures, NHS guidance puts the added chance of miscarriage at about 1 in 200. It varies with the doctor's experience and your own pregnancy. Ask the doctor doing the procedure what the figure is in their own practice, and weigh it against how much knowing the result matters to you.
Does it hurt?
Most women describe it as uncomfortable rather than painful. The skin is often numbed first. You may feel pressure or a cramp like a period pain as the needle goes in, and for a short while afterwards. It is over in a few minutes, and you can bring someone to sit with you.
Do both parents need to come?
It helps a great deal. The lab needs a blood sample from both parents to identify each person's exact gene change, unless this has already been done. It also means you hear the same explanation together, which makes the later decision easier to share.
Can I travel home to my district the same day?
Most women go home the same day. If home is a long bus or car journey, ask the centre whether you should rest nearby first. Avoid heavy lifting and hard work for the rest of the day. Know the nearest hospital on your route in case you have bleeding or leaking fluid.
My Rh blood group is negative. Does that change anything?
Tell the team before the procedure. If your blood group is Rh negative and the baby's father is Rh positive, you may be offered an injection afterwards to protect this pregnancy and future ones. The team decides this from your blood group report, so bring it with you.
Can the same sample test for sickle cell disease too?
Yes, if the lab knows what to look for. The same sample can check for thalassaemia, sickle cell disease and combinations such as sickle beta thalassaemia. That is why both parents' carrier and DNA reports matter. Make sure the centre has copies of all of them before the day.
Is the procedure covered by Aarogyasri or insurance?
Coverage varies, and scheme rules change. Some government programmes for thalassaemia and sickle cell support screening and counselling. Ask the centre in advance, and check the current rules for Aarogyasri, PM-JAY, CGHS or your insurer. Get the answer in writing if you can.
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Sources
- NHS — Chorionic villus sampling (CVS)
- NHS — Amniocentesis
- NHS — Thalassaemia
- National Heart, Lung, and Blood Institute — Thalassemia
- National Health Mission — Sickle cell mission portal
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 Thalassaemia and Sickle CellThe full pathway from carrier report to resultBoth Partners Are Carriers: What the Odds MeanWhat the chance means for each pregnancyGenetic Counselling for Haemoglobin DisordersWhat to expect before you decide on testingIVF and Preimplantation Testing for ThalassaemiaTesting embryos before a pregnancy beginsCarrier Screening and Genetic CounsellingThe full guide to carrier testing
Talk to us
Both of you carriers, and already pregnant?
Tell us what your reports say. A CION haematologist will read them with you and help you reach a foetal medicine centre quickly.