9 March 2016

Amniocentesis: Yes or No?

So here you are: maybe you have a 'high risk' result from a combined screening test for T18; maybe you've just had your 20-week scan and they've picked up a bunch of anomalies that they suggest mean T18; maybe you've got a positive result from a Harmony or similar non invasive fetal screening test for T18. Either way you are being offered amniocentesis to confirm the diagnosis and you're not sure whether to have it.

Why might you choose to have an amnio?

  • You plan to terminate your pregnancy if the amnio shows your baby does have T18.
  • You want to get pregnancy management and/or post birth treatment plans in place prior to birth
  • Having a confirmed diagnosis will affect your pregnancy management or birth decisions.
  • You don't do well with uncertainty; you want a confirmed diagnosis and are prepared to take the risk of  miscarriage for certainty.

Why might you choose not to have an amnio?

  • Risk of miscarriage - amnio definitely carries a risk of miscarriage. I will discuss the controversy about this risk below.
  • Confirmed diagnosis will mean that initial treatment is likely to be denied at birth - a lot of people in the trisomy world think that confirmation will lead to denial of initial treatment. In a world where babies with T18 are routinely denied treatment, they have a point.
  • You don't intend to do anything with the result - you are prepared to let nature take its course. You neither want active treatment for a living baby nor to terminate your pregnancy.


How likely am I to have a miscarriage after amniocentesis?

This is very unclear. The quoted miscarriage risk for amniocentesis is 0.5 to 1%. This rate appears to be based on three studies from the 1970s from the US, Canada and the UK which gave a 0.5% rate of loss. This was before ultrasound guidance was routinely used. Another UK study from the 1980s gave a 1% rate of loss, which is often quoted in the UK. However, concerns have been raised about the background loss rate in the non-amniocentesis group which was unexpectedly low, meaning that the amniocentesis loss rate looked higher.

More recent studies have concluded that the rate of loss is much lower. One such study, of 35,003 women with a viable singleton pregnancy in the general population, of whom 3,096 had amniocenteses, suggested that the rate of miscarriage was a negligible 0.06%. In another study, Washington University Medical Center analysed its amniocentesis outcomes from 1990-2006 and concluded that the rate of loss was 0.13% above the baseline rate. However, a literature review from 2011 found an average pregnancy loss rate of 1.9%, with wide variation between studies (from 0.2% to 2.9%).

So what can we say? Probably only that:
  1. There is a risk of miscarriage, but it is unclear how high. At worst it would likely be around 3 in 100  pregnancies (3%). It may be negligible - as low as 6 in 10,000 pregnancies (0.06%).
  2. There is such a wide variation between studies that it makes sense to conclude that there may be unit and operator differences in miscarriage rates. If you choose to consider amnio, it may be worth asking the individual rates for your hospital and the doctor who will perform it (if they'll give them to you!) 
Links to the research this is based on can be found here. 

Is a 'positive for T18' screening test as good/as bad as amnio?

Do you treat a positive screening test or suspicion of T18 as definitive? And will your medical team treat it this way? How does it benefit or disadvantage you and your baby if they do?

A common argument for not doing an amnio is that a positive screening test or high suspicion of T18 gives you many of the advantages of diagnosis (time to prepare, make plans, etc.) but leaves enough doubt that they cannot deny initial treatment to your baby at birth.

This likely depends on the screening test, on your medical providers and on what your plans are.

Types of test

A positive Non-Invasive Fetal Test (NIFT) result - eg. Harmony, MaterniT21 - is highly reliable. It is likely, if you have a 'positive for T18' result from one of these, that unless you have one of the risk factors for a misdiagnosis, your baby does indeed have T18.

A positive combined screen (nuchal and blood test) simply means you have higher than a 1 to 1.5% chance of your baby having T18. 1-2 in 100 may be 'high risk' but there is still a 98-99% chance that your baby does not have T18.

Suspicious ultrasound findings for T18 (see this PDF for the sonographic markers) can be strongly indicative of T18, or can merely indicate a possibility of it. Sometimes you may end up in a situation where T18 is one of a range of possibilities, with other genetic syndromes also realistic possibilities.

If you have a positive combined screen or suspicious ultrasound findings (or indeed both) you can choose NIFT for a more accurate screening result at that point rather than moving onto amnio, or you can move onto amnio.

How do medical providers treat positive screening results?

If you decline amnio, a medical provider is likely to treat a high-risk combined screening result or suspicious ultrasound findings as if your baby does not have T18. Your pregnancy will be managed as any other and your baby will be given initial treatment at birth, the same as any other. If your baby shows markers of T18 after birth, they will screen the baby and may discuss withdrawal of treatment with you at that point.

In the case of a positive NIFT result, it is less clear cut. I have heard of medical providers treating a positive NIFT the same as a positive amnio and denying treatment on that basis. They are possibly on shaky ground in doing so, as nobody claims NIFT is a diagnostic test. You could certainly take advantage of the doubt to insist on clinically needed post-birth treatment. Other providers will treat a positive NIFT result the same as any other positive screening test, and will manage the pregnancy and offer post-birth treatment as if there is no T18.

I want full treatment for my baby. Is it best to have a confirmed diagnosis or not?

I would say yes, but this is not a universally shared opinion.

My view is that:
  • A confirmed diagnosis means you can agree post-birth care plans while you have the time and energy to do so (ie. before your baby arrives).
  • A confirmed diagnosis means you can ensure that your pregnancy is managed appropriately to minimise the high risk of stillbirth.
  • A confirmed diagnosis means you can get agreements in place for monitoring in labour and interventions if needed.
  • A confirmed diagnosis means you can seek other healthcare providers if you can't get agreement from your current providers (after birth you're pretty much stuck).
  • A confirmed diagnosis means you have time to manage disagreements if you stick to your current providers. You are absolutely stuck if they refuse to ventilate at birth: you have no time to argue, no options at all. If you've argued that point in pregnancy and can't reach agreement, you can escalate. Even go to court if needed and have agreements in place for when your baby is born.
I would say that either an amnio/CVS confirmation or a NIFT result that your provider agrees to treat as a positive is sufficient as a 'confirmed diagnosis'.

Others, however, would say that:
  • A confirmed diagnosis means you can be denied treatment. If your negotiations are unsuccessful and you have nowhere suitable to transfer to, then you are absolutely stuck.
This may be the case if you live in an area which is very hostile to treating babies with T18, where negotiations have failed for other families or you sense from your initial conversations that they are likely to fail for you. You have no options for alternative care providers and you are not willing to pursue the case to court (or you may lose in court). It is worth considering your situation before opting for invasive testing, as it may affect your decision.

I want palliative care for my baby. Is it best to have a confirmed diagnosis or not?

Again, I would say yes:
  • A confirmed diagnosis means you can access palliative care teams, children's hospices and community nurse teams in pregnancy.
  • A confirmed diagnosis means you can agree a limited care plan pre-birth, so your baby will not receive invasive treatment you don't want.
  • A confirmed diagnosis means you can discuss decisions and options regarding where your limits lie, what treatments you will accept and how you will manage your baby.

I would say that in this case you need an amnio, not a NIFT. I feel that doctors are on shaky legal ground denying care on the basis of a positive NIFT, which is acknowledged to be a screening test (though I have known it happen). It is therefore likely that the baby will have to be given invasive treatment until diagnosis is confirmed post birth, even if this is against your wishes. Some providers may agree to treat a positive NIFT result combined with suspicious ultrasound findings as confirmation of T18.

I want to terminate my pregnancy if my baby has T18. Should I go for amnio?

No responsible healthcare provider would agree to terminate a pregnancy for T18 without confirmation via amnio. However, in the UK, you can terminate for any reason whatsoever with the agreement of two doctors up until 24 weeks gestation, so you can terminate on the basis of a positive screening test if you wish. Some parents may be comfortable terminating on the basis of a positive NIFT or gross fetal anomalies on ultrasound scan.

If you are in the situation of a positive combined screening test or suspicious ultrasound findings, you could opt for NIFT instead of amnio to avoid the risk of miscarriage and only opt for amnio if the NIFT is positive.

However, it is worth remembering in this situation that:
  1. This will delay your termination if the tests are positive. NIFT results take 1-2 weeks to come back in the UK. Add another few days for amnio, plus time to arrange the tests.
  2. NIFT only tests for a limited number of chromosomal anomalies (the main three trisomies plus sex chromosome anomalies) and amnio will identify a wider range of genetic problems. If you have a negative NIFT with a positive combined screening or suspicious ultrasound findings, will you want an amnio anyway?

The decision about whether to opt for amniocentesis is never easy, but by weighing up all the factors, you will come to the best decision for you and your baby.

No comments:

Post a Comment

Comments appear with some delay to allow moderation. Thanks for commenting!