Prenatal Diagnosis: CVS or Amnio

What does prenatal diagnosis mean?

This is when your baby is checked for genetic disorders, before your baby is born.  This enables you to make important decisions about the healthcare of your foetus such as, having special treatment ready right after delivery.  In some cases, parents may also decide not to continue a pregnancy or made aware of what to expect in case they elect to continue with the pregnancy. This is also allows the healthcare providers to counsel you more appropriately.

The most common condition tested for is Down Syndrome.

What are the tests and who should have them?

Amniocentesis and chorionic villus sampling (CVS) are tests that help find genetic disorders before birth.  They are not necessary for all pregnant women to have, but can be recommended if you have: high risk result at nuchal translucency scan, findings of major structural anomalies at morphology scan, advanced maternal age, family history of genetic problems, High risk on NIPT result etc. Amniocentesis and CVS are definitive diagnostic tests with very high accuracy.

These are invasive tests; hence they carry a small risk of miscarriage. Patients are counselled appropriately before the test and written consent is obtained.

At what stage are they performed?

A CVS is usually performed between the 11th and 14th weeks of pregnancy and an Amniocentesis is performed during the 15th week of pregnancy or even later.


How is an Amniocentesis performed?

This is performed by inserting a thin needle through your abdomen into your womb (uterus) under ultrasound guidance and withdrawing a small amount of amniotic fluid (the fluid around the baby). Don’t worry, this will not hurt your baby and your body will easily replace the fluid that was removed. The fluid is then sent to a laboratory for evaluation.

Your doctor may tell you to rest after the test but normally you can resume normal activity the next day. You may experience abdominal cramps following the test for which you can take analgesics eg paracetamol.

How is a CVS performed?

This can be done via the abdomen or cervix.  A sample of placenta (nourishment for the baby) is removed from your uterus via either a catheter (a thin tube) or a needle. The cervix approach, a catheter is inserted into your vagina and through the cervix and the sample is withdrawn. The abdominal approach, local anaesthetic is given and the sample can also be obtained by inserting a needle into your abdomen and withdrawing some of the placenta.

Although most women feel fine after the test, you may experience some mild cramping afterwards for which you can take analgesics eg paracetamol.

When will the results come back?

The samples are sent to a Cytogenetic lab for full chromosomal analysis, microarray or full karyotype. The results take approximately 10 working days to be completed.

A faster result can be obtained in 2 days by using a technique called QF-PCR but this covers only a few chromosomes i.e. 21, 18, 13 and X and Y.

It is recommended for parental blood samples to be taken as well to accompany these samples.

We will phone you and notify the referring clinician of the results.

What to observe/know if you are booked for CVS or Amniocentesis:

Bring someone with you to accompany you home.

You will be counselled for the test, written consent will be obtained, and baby will be scanned again to assess the best approach to undertake for the test

Following the procedure mild cramping is expected which can be managed with analgesics. If severe cramps, fever, bleeding or leaking of fluid is noted you need to notify us and your doctor.

We need to know your blood group so that in case you are Rhesus Negative we can give you Anti D

If you are on blood thinning medication eg asprin or clexane let us know so that we advise accordingly

The lab will send a separate bill to you but a significant amount is covered by Medicare.

In case of any concerns contact us on 02 8847 2200 and speak to Dr Robert Magotti


Non – Invasive Prenatal Testing (NIPT)

NIPT is regarded as an advanced screening test. NIPT involves a maternal blood test following counselling. The test is recommended after 10 weeks’ gestation and beyond.

Foetal cell free DNA is identified and is tested for some of the common chromosomal problems eg Downs, T18, T13, sex chromosomes and several others.

Not all chromosomal problems can be detected by NIPT and it definitely can’t detect structural problems.

It is recommended for NIPT to be preceded by counselling, scanning to date the pregnancy and rule out major structural anomalies and then followed by blood sampling. Results will come back in 5 – 10 working days and we will call you for results.

At our practice unless indicated otherwise by our referrers we recommend this test to be undertaken between 12 -13 weeks to allow for a better foetal anatomy scan to be performed.

If the NIPT test is abnormal or inconclusive, an invasive test is recommended.

Currently NIPT is not covered by Medicare.