Update on Less invasive prenatal testing

Update

Non-invasive tests have become cheaper and are more available to women in rural areas.

The basic Harmony test (trisomy 13, 18 & 21)  now costs $425. A Medicare rebate is not available for this test.

Another local lab offers a basic Generation test costing $395 and an extended test for $695

I have refined what I offer in the last last few year,

  1. Will offer a dating scan to confirm dates
  2. NIPT after 10 weeks if you can afford it
  3. First trimester ultrasound and screening bloods  if you have had a NIPT, or risk assessment if no NIPT. This is done between 11 to 13+6 weeks.

 

 

31 March 2018


 

The most recent ANZJOG  has two papers and an editorial about non-invasive prenatal testing for certain fetal genetic disorders.

This should really be called less invasive as unlike some DNA testing it does require a blood specimen. But it is certainly less invasive than an amniocentesis or chorionic villus sampling (CVS) with the attendant risk of miscarriage.

Although operator dependent, the risk of miscarriage with CVS is between 1:100 to 1:200; whilst there is less risk from an amniocentesis; 1:200  to 1:300. CVS can however be performed earlier in the pregnancy.

The risk of miscarriage and stillbirth may be increased by factors such maternal age and weight, previous miscarriage, or stillbirth, low PAPP-A, high  high fetal nuchal translucency, pre-existing diabetes, ovulation induction. chronic hypertension and smokers.

Obviously it would not be acceptable to do these tests on all pregnancies. Not every woman want to know her child’s genetics. To many the option ending a pregnancywith Down Syndrome is unacceptable.

In South Australia, screening  done by SAMSAS at the Women’s & Children’s Hospital.

Screening requires

  1. blood at 9 to 13 weeks
  2. nuchal translucency at 11 to 13+6 weeks

For practical purposes I usually organise testing at 11 to 12 weeks with the ultrasound first to confirm dates then the blood drawn if dates are accurate.

The detection rates for Down Syndrome with this test are

  • Serum biochemistry alone 70.1%
  • Ultrasound alone 72.7%
  • Serum biochemistry + Ultrasound 88.3%

I offer screening to all pregnant women as a way to better define the risk of having a baby with Down Syndrome than age alone. For an estimate of age related risk I use SAMSAS update 15.

I use the risk of greater than 1:250 to recommend an invasive test. If the test then identifies an abnormality, the woman may be offered a termination of the pregnancy. I usually offer my personal view that if I would never terminate a pregnancy then I wouldn’t undertake the screening test.

Some women still want to know more about their risk but baulk at the risk of the CVS or amniocentesis. For them the non-invasive test is attractive.

For women who fall into the more than high risk screening group the non-invasive test is also attractive.

For a paper on the science of the test you may read The use of cell-free fetal nucleic acids in maternal blood for non-invasive prenatal diagnosis by Wright C, Burton in Human Reproduction Update, Vol.15, No.1 pp. 139–151, 2009)

Currently in Australia, non-invasive tests have some limitations.

There is no consensus on it utility.

There is no Medicare funding; nor is it covered by private insurance companies. The test cost will $900 to $1250.

The blood test has to be done in a major capital city on a specific day. So there is the cost of the journey to consider. The blood is then flown to the US for testing. Interestingly, Tasmanian women can have it done at the Royal Hobart but pay a $100 premium over those in Melbourne.

There is a wait for 7 to 10 days.

Accuracy is dependent upon fetal DNA yield.

The tests may be performed from 9 weeks which is prior to the nuchal translucency ultrasound and would necessitate a dating scan if dates are uncertain.

Some companies offer a second free test is the first is inconclusive.

Current tests in Australia

QML/Laverty/Western/Abbott offer Generation
SNP/ClinPath offer Harmony
VCGS offer percept
IVF Australia group offer Panaroma

And honestly, I’m note sure which is the best.

NIPT

Where does this technology fit into my practice?

Hui and Hyett have discuss how this new technology should fit into Australian screening. Hui, L and Hyett J. Noninvasive prenatal testing for trisomy 21: Challenges for implementation in Australia Australian and New Zealand Journal of Obstetrics and Gynaecology 2013; 53: 416–424

How would I decide who to offer the test to?

  • following a high risk screen
  • maternal age
  • family or personal history
  • genetic condition
  • everyone who can afford it?

The American College of Obstetricians and Gynecologists Committee on Genetics issued a  position statement on non-invasive prenatal testing for fetal aneuploidy in December 2012:  

“Noninvasive prenatal testing that uses cell free fetal DNA from the plasma of pregnant  women offers tremendous potential as a screening tool for fetal aneuploidy. Cell free fetal  DNA testing should be an informed patient choice after pretest counseling and should not be  part of routine prenatal laboratory assessment. Cell free fetal DNA testing should not be  offered to low-risk women or women with multiple gestations because it has not been  sufficiently evaluated in these groups. A negative cell free fetal DNA test result does not  ensure an unaffected pregnancy. A patient with a positive test result should be referred for  genetic counseling and should be offered invasive prenatal diagnosis for confirmation of test  results.”

I believe that RANZCOG and RCOG are still considering how this test fits into their guidelines for prenatal testing.

For the time being, given I do not do CVS or amniocentesis my plan is to continue to offer all my pregnant patient the SAMSAS screen and if they can afford the test to discuss it with the obstetrician in the tertiary centre prior to undergoing an invasive test.  I know some women would struggle with the cost but the test may well avoid having a CVS or amniocentesis with its attendant risks.

4 thoughts on “Update on Less invasive prenatal testing

  1. Your conclusion is also my practice as well. I used to also think about discussing with the women not going through with the screening if they would not consider termination anyway. I have recently changed my practice on this and now talk about still offering the testing anyway because if the child is very high risk for Down’s it may allow the family to educate themselves and mentally prepare themselves for the possible eventuality that their child may have a genetic syndrome and prepare for the comorbidities and challenges that are related to this.

    Also, I assume you mean Nuchal Translucency from 11 weeks not 1 week? (Typo?)
    Cheers, Rob.

    • Fixed the typo thanks.

      Do you want to know or not?

      Do you spend 6 to 7 months thinking about having a potentially disabled child on the basis of a screening test alone and then be relieved that child appears normal when it is born?

      Pregnancy can be a stressful time for parents without that hanging over their head. Is is better to blissfully unaware?

      Something that I also tell parents is that knowing their child’s chromosome doesn’t tell them about who their child will be. I’m certain that a lot of evil bastards in history had 46 healthy chromosomes

      This is where a good GP has the advantage, if you don’t already, you can make the time to get to know your patient.

      • Yeah great points. I guess it is up to the patient. My role is to have them as informed as possible when they make their decision. A good relationship with them will help this.

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