Amniocentesis

Medically reviewed by Dr Darshana Ajmera, MBBS (Nair, Mumbai), MS ObGyn (Honours) - Obstetrician, Gynaecologist & Fetal Medicine Specialist

What it is

Amniocentesis is a test in which a fine needle is passed through the abdominal wall into the uterus, under continuous ultrasound guidance, to draw off a small sample of the amniotic fluid surrounding the baby. That fluid is not just water. It carries cells shed from the baby’s skin, lungs and urinary tract, and those cells carry the baby’s chromosomes and genes.

That single fact is what makes amniocentesis different from everything that comes before it. A double marker test, a quadruple test or an NIPT can tell you how likely a condition is. Amniocentesis tells you whether it is there. It is a diagnostic test, not a screening test, and in my clinic that distinction is usually the reason a woman is sitting in front of me at all.

Who needs it

Amniocentesis is offered to a small, specific group of pregnancies - not routinely, and never simply because of age alone. We consider it when:

• A screening test has come back high risk. A high-risk NIPT, double marker or quadruple test is a signal, not a diagnosis, and amniocentesis is how we settle it.
• The anomaly scan has shown something structural - a heart defect, a thickened nuchal fold, a kidney or brain finding - which raises the chance of an underlying chromosomal cause.
• A previous baby or pregnancy had a chromosomal or genetic condition.
• One or both parents carry a known genetic condition. In our part of the country beta thalassaemia carrier status is the commonest reason, along with spinal muscular atrophy, Duchenne muscular dystrophy, and haemophilia.
• There is a family history of a condition that can be tested for in fetal cells.
• An intrauterine infection is suspected - the fluid can be tested for organisms such as CMV or toxoplasma.
• Occasionally for treatment rather than testing - draining off excess fluid when polyhydramnios is causing real distress, which is called amnioreduction.

“My NIPT came back high risk for Down syndrome. Isn’t that enough to know?” No, and this matters more than almost anything else I say in that consultation. NIPT is a very good screening test, but it reads fragments of placental DNA in your blood, not the baby’s own cells, and it can be wrong in both directions. I have looked after women who went through weeks of grief on the strength of an NIPT result that amniocentesis later showed to be normal. Before any irreversible decision is made about a pregnancy, we confirm with a diagnostic test. Please do not let anyone rush you past that step.

How it is done

Timing. Amniocentesis is done from 15 completed weeks onwards, most often between 15 and 20 weeks. It is not done earlier, because before 15 weeks the risks rise and there is less fluid to spare.

The scan comes first. We check the baby’s heartbeat, confirm the dates, look at where the placenta is sitting and find a good pocket of fluid away from the baby. This planning takes longer than the needle itself.

Preparation. You lie on your back, the skin of the abdomen is cleaned with antiseptic and covered with a sterile drape. Your bladder should be empty. No shaving, no fasting, no drip.

The needle. A very fine spinal needle is passed through the skin and the uterine wall into the chosen pocket of fluid, with the ultrasound probe watching it the whole way. About 15 to 20 ml of fluid is drawn into a syringe - roughly a tablespoonful, which the baby replaces within hours. The needle is then withdrawn.

Afterwards. We check the baby’s heartbeat again on the scan, put a small dressing on the skin, and keep you lying down for a while. If your blood group is Rh negative, an anti-D injection is given. The fluid goes straight to the genetic laboratory.

From walking in to walking out, expect about half an hour in the procedure room. The part with the needle in it lasts under a minute in most cases.

Anaesthesia, duration and hospital stay

There is no general anaesthesia and no spinal for amniocentesis. Local anaesthetic in the skin is optional and often skipped, because numbing the skin involves a needle of its own.

The procedure takes five to ten minutes including the scan, with the needle itself in place for under a minute.

It is a day-care test. You rest in the hospital for one to two hours afterwards, we listen to the baby again, and you go home the same day. No admission, no overnight stay.

Results. A rapid test on the fresh fluid - FISH or QF-PCR - gives an answer on the common chromosome conditions in two to four days. The full chromosome analysis needs the cells to be grown in culture and takes two to three weeks. A chromosomal microarray takes about two weeks. Single-gene tests, such as those for thalassaemia, run on their own timeline, which we will tell you in advance.

Recovery

The rest of the day. Go home, keep your feet up, eat normally. A dragging period-like ache low in the abdomen for a few hours is expected. Paracetamol is safe if you need it.

The first two or three days. No gym, no heavy lifting, no long journeys, no intercourse, no swimming. Light housework and a desk job are fine from the next morning if you feel well. A little soreness at the needle site is normal.

The first week. By now you should feel completely ordinary, and a good number of women go back to work the very next day. Fetal movements carry on as before - if anything felt different at first, it settles.

Weeks 2 to 4. Physically, there is nothing left to recover from. What is left is the waiting, and I will not pretend that is easy. The wait for a chromosome report is the hardest part of this test for most families, far harder than the needle. Ask us for the rapid result as soon as it is available rather than sitting at home guessing, and call the clinic if the waiting becomes more than you can carry.

By 6 weeks. You are back in ordinary antenatal care, with your results in hand and a plan built around them.

Come in straight away, at any hour, for fever, fluid leaking from the vagina, bleeding, cramping that keeps going, or a change in the baby’s movements.

Amniocentesis, CVS or NIPT - which test, and when

This is the comparison families actually want, and each of these three has a job it does better than the others.

• NIPT is a blood test from the mother’s arm, done from 10 weeks, with no risk to the pregnancy at all. It is only a screening test. It is very good at telling you that the common trisomies are unlikely, and much less reliable when it flags a problem. A high-risk NIPT needs confirming.
• Chorionic villus sampling (CVS) takes a tiny sample of placental tissue at 11 to 14 weeks. It gives a diagnostic answer earlier than amniocentesis, which matters when a decision has to be made about continuing the pregnancy. Its procedure-related risk is slightly higher than amniocentesis, and it cannot test for infection or neural tube markers.
• Amniocentesis is done later, from 15 weeks, but it is the most established diagnostic test, carries the lower procedure risk of the two invasive tests, and can also be used to look for infection.

Put simply: NIPT to screen, CVS when you need a diagnosis early, amniocentesis when you need a diagnosis reliably. Our fetal medicine team will help you work out which of the three fits your pregnancy, and you can see all the procedures we perform alongside it.

Risks and complications

I would rather you hear these from me before the test than read them afterwards.

• Miscarriage. The figure quoted in counselling for years was under 1 in 200; modern estimates from experienced centres are lower. Small, but real, and the risk that matters most in your decision.
• Leaking of amniotic fluid, usually a small amount that stops on its own within a day or two.
• Cramping and spotting in the first day.
• Infection of the uterus, rare but serious, which is why fever is never something to sleep on.
• Needle injury to the baby, very rare with continuous ultrasound guidance.
• Rhesus sensitisation in an Rh negative mother - prevented by the anti-D injection.
• A dry tap or a blood-stained sample, occasionally needing a second attempt on the same day or a repeat later.
• Culture failure in the laboratory, so the cells do not grow and the test has to be repeated.
• An unclear result - a variant whose meaning is not yet known. These are uncommon but genuinely difficult, and they are handled with proper genetic counselling, not a phone call.
• A normal result that is not a guarantee. Amniocentesis answers the questions it was asked. A normal chromosome report does not promise a baby free of every condition, and we will be clear with you about what your test covers.

Alternatives

NIPT, if what you want is reassurance rather than certainty and you accept that a positive result will still need confirming.

CVS, if you are early enough in the pregnancy and need a diagnostic answer sooner than 15 weeks.

A detailed anomaly scan, with fetal echocardiography, which can tell you a great deal about structure without any needle at all. Our ultrasound and fetal imaging service does this work routinely.

Fetal blood sampling (cordocentesis), reserved for specific situations such as severe fetal anaemia, and carrying a higher risk than amniocentesis.

Testing the parents instead. For carrier conditions such as thalassaemia, testing both parents first often removes the need to test the baby at all.

Declining invasive testing. This is a legitimate, thoughtful choice, not a failure. If the result would not change how you carry or care for this pregnancy, then monitoring with scans and preparing for the baby you are having can be the right plan. My job is to lay out the options, not to push you down one of them.

What it costs

We have not published a fixed price for amniocentesis, because the test is rarely just the test. The final amount depends on:

• Which laboratory tests are ordered on the fluid - a rapid FISH or QF-PCR alone, a full karyotype, a chromosomal microarray, a single-gene test for thalassaemia or another specific condition, or an infection panel. This is by far the biggest factor.
• Whether a rapid result is requested alongside the full report.
• The scans done before and after the procedure, including a detailed anomaly scan or fetal echocardiography.
• Whether anti-D is needed for an Rh negative mother.
• Genetic counselling sessions before and after the result.
• Whether the procedure needs to be repeated for a failed sample or a culture failure.
• Whether it is combined with any other procedure in the same sitting.
• Your insurance or TPA cover, and whether the visit is pre-authorised.

Please call +91-8668954915 and we will put together a written, itemised estimate for your own situation before you commit to anything.

Preparing for your test

• Bring every report you have - all your scans, your screening test result, blood group, and any records from a previous affected pregnancy.
• Know your blood group and your husband’s, because of the anti-D question.
• Eat and drink normally. There is no fasting. Come with an empty bladder.
• Tell us about blood thinners or any medicine that affects clotting, and about allergies to antiseptics or dressings.
• Wear something loose that gives easy access to your abdomen.
• Bring someone with you. Not because you will be unwell, but because it is not a morning to sit through alone.
• Ask for counselling before, not after. Decide in advance what you would do with each possible result - that conversation is far easier before the needle than after the report.
• Keep the next two days light and arrange help at home if you have a small child.
• Save our number and know how you would reach us at night if you needed to.

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If a screening test or a scan has raised a question about your baby and someone has mentioned amniocentesis, come and talk it through properly before you decide anything. The fetal medicine team at Shubham Hi-Tech Hospital and Test Tube Baby Centre, Amravati, will go through your reports with you, explain what the test can and cannot tell you, and support whatever you choose from there. Call +91-8668954915 or get in touch here.

Disclaimer: This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor for guidance specific to your situation.