Amniocentesi? No, grazie.

Miscarriage FearsRead – Expecting Better: Why the Conventional Pregnancy Wisdom is Wrong and What You Really Need to Know by Emily Oster

Quando ti ritrovi incint* ti chiedi che fare con gli screening invasivi sul bambino che porti in grembo…

… There is one major medical decision to be made in the first trimester of pregnancy: antenatal screening…

È giusto sottoporsi all’amniocentesi? La risposta ha una robusta componente soggettiva

… thinking about these pluses and minuses for you, personally. I’d argue that no two people will think about this decision quite the same way. Which is why even having a “standard” recommendation here makes so little sense to me…

Lo scopo dei test…

… The goal of all antenatal screening and testing is the same: to learn whether your baby has a chromosomal abnormality…

Il problema dei cromosomi

… Human DNA has 23 pairs of chromosomes. The vast majority of chromosomal problems are caused by having three copies of a chromosome rather than the normal amount of just two….

La sindrome di down e altri problemi…

… The two other common ones are Edward’s syndrome (three copies of chromosome 18) and Patau syndrome (three copies of chromosome 13). These are more severe than Down’s syndrome…

Nell calcolo dei rischi l’età della donna è fondamentale.

L’esempio della trentunenne…

… I was 31 when Penelope was born. This put my risk around 1 in 700. This means that of 700 women my age who get pregnant, on average 1 of them will carry a baby with Down’s syndrome…

L’amniocentesi è un test dagli esiti praticamente certi, viene raccomandato sopra i 35 anni

… This test accurately detects Down’s syndrome and the other chromosomal abnormalities, but carries a small risk of miscarriage. Because of the relationship between these problems and maternal age, it was common to offer this test only to women over 35…

Tavola dei rischi…

… Risk of Down’s Syndrome by Age . . . Age Chance of Down’s syndrome 20–24 1 in 1488 25–29 1 in 1118 30–34 1 in 746 35 1 in 374 36 1 in 289 37 1 in 224 38 1 in 173 39 1 in 136 40 1 in 106 41 1 in 82 42 1 in 63 43 1 in 49 44 1 in 38 45 1 in 30 . . . and some comparisons Car accident within next year: 1 in 50 Audited within next year: 1 in 200 Injury with fireworks within next year: 1 in 19,000 Winning Powerball: 1 in 80 million…

Esistono esami meno invasivi ma che danno info meno sicure…

… in the last 20 years doctors have made enormous progress on antenatal screening. This screening uses information from an ultrasound and from a blood test in addition to information about your age to make a more precise guess about the chance that your baby has a chromosomal problem. The advantage to the screening option is that it carries no miscarriage risk. The disadvantage is that it cannot tell you for sure whether your baby is affected…

Opzioni disponibili…

… Option 1: Do nothing… Option 2: Start with the antenatal screening… Option 3: Skip right to the invasive testing…

Se chiedi ai dottori, loro si mantengono sul vago. Non resta che far da soli.

… I asked my doctor. She had recommended the screening test (the non-invasive option), so I asked a simple form of my question. If that test went well, what would my risk be? I was told it would be “very low”. “How low?” I asked. “One in a thousand? One in ten thousand? One in thirty thousand?” “Yes,” was the response, “something like that.” I am willing to accept that I’m perhaps a little more neurotic about exact numbers than most people, but this seemed extremely vague: 1 in 1,000 and 1 in 30,000 are quite different… I realised that if I wanted an answer to either of these questions I’d have to do some digging on my own…

Spoiler…

… Spoiler alert: in the end, I felt optimistic about everything. The non-invasive screening tests are really good. After a good result, my remaining risk would probably be something like 1 in 6,000, which, even by my high standards, is very small…

L’inconveniente del test invasivo…

… The invasive testing has also got hugely better over time. The CVS test (clearly the better option) carries only a tiny risk of miscarriage, much lower than the 1 in 200 figure that was suggested…

Ma come funzionano i test non invasivi?

Giudico da quel che vedo. Un po’come con le angurie…

… try to figure out whether the fruit is ripe by looking at things you can see on the outside. What colour is it? How does it smell? People have all sorts of tricks for doing this… Take the colour. On average, melons that have some green rind are less likely to be ripe…

La marca del down nella translucenza…

… In the case of Down’s syndrome, there are three markers the doctor is looking for in the first trimester screen. The most useful of these is a measurement of the amount of fluid behind the baby’s neck (called the nuchal translucency, or NT). Foetuses who have Down’s syndrome are much more likely to have a lot of fluid behind the neck. Doctors also measure two hormones in Mum’s blood (PAPP-A and HCG). Women who are carrying foetuses with Down’s syndrome also tend to have different hormone levels than those whose babies have normal chromosomes…. Why use both hormones and the fluid scan rather than just one or the other? Simple: if you have more signals, you can learn more…

La translucenza consente di aggiornare il calcolo del rischio…

… After doing all these measurements, your doctor will tell you a new level of risk. This risk will be based on these new measurements and also on your age. Your old risk was based only on your age…

Il rischio è un numero. Esempio…

… Based on your age and the blood test and the ultrasound, your foetus has a 1 in 500 (or 1,000 or 10,000) risk of having a chromosomal problem…

Quando fare altri test? Le raccomandazioni ufficiali

… If your final risk is higher than 1 in 250 (say, 1 in 200), you’ll be told that you should undergo more extensive testing…

Ma quanto è affidabile il test per le info fornite?…

… I needed to know how accurate these tests were at detecting chromosomal problems. If my final risk was above the cut-off and they told me “Everything is great, do nothing!” how confident could I be?… The answer to my first question about detection rates: about 90 percent. That is, doctors can detect 9 out of 10 Down’s syndrome cases using this screening procedure…

Lo studio decisivo…

… Among the best is a study in England of about 57,000 pregnancies. This study found that the first trimester screening could detect 91 percent of Down’s syndrome cases… The researchers reported a 6.3 percent false positive rate. This means that for every 100 women tested, about 6 of them were told they were positive but in fact their babies turned out to be perfectly healthy…

Due concetti decisivi…

detection rate: what percentage of Down’s syndrome cases will be identified by this test?… false positive (i.e., you are told the screen is positive, but, in fact, your baby is healthy)…

L’esempio di una 31enne

… I was 31. My initial risk was about 1 in 700. If I did this screening, about 89 percent of Down’s syndrome cases would be detected. Taking into account the few false positives, my final risk would go down by about almost a factor of 10, to about 1 in 6,000.** You know, somewhere between the chance of a midwife delivery and the risk of blanket injury, but just a bit more precise…

***

Perché le donne fanno tutti questi esami nel primo trimestre?…

… at this point in the pregnancy, most women are not showing and may not have told many people they are expecting. This may lessen the burden of making a difficult choice about continuing the pregnancy…

Oltre alla sindrome di down esistono altre patologie…

… this same screening procedure is also effective at detecting trisomy 18 and trisomy 13 (Edward’s and Patau syndromes, respectively). These conditions are much rarer – trisomy 18 occurs in about 1 out of 5,000 live births and trisomy 13 in 1 out of 10,000 – and both are typically fatal within the first year of life. The risk of these conditions also varies by age…

Su queste gravi patologie le info fornite dai test sono anche migliori…

… The screening test for these diseases works just like described above, only better: detection rates are very good (much better than for Down’s syndrome) and false positives are rare…

Riassuntino…

… The Bottom Line: Part 1 • First trimester screening can detect about 90 percent of Down’s syndrome cases. • The success of this screening varies with age, from around 82 percent in women age 20 to almost 98 percent in women over 40. • False positives also vary with age, from 3 percent for someone in her early twenties to 50 percent for someone in her mid-forties…

***

Test invasivi: amniocentesi e CVS…

… Both of these tests would allow my doctor (or, more accurately, some lab) to actually sequence our daughter’s DNA and would tell us for sure if she was healthy…

Come funziona l’amnio?…

… the doctor extracts from the uterus a sample of the baby’s cells. The two differences are where those cells come from and at what stage of pregnancy the procedure is performed…

Quando farla…

… This procedure is typically performed between sixteen and twenty weeks of pregnancy (doing it much earlier appears to increase the risk of club foot, so is generally avoided)…

CVS, una nuova procedura…

… Amniocentesis has been around for decades. CVS is newer – it was introduced in the early 1980s – but has become increasingly popular over the past ten years. In a CVS test, the cells are taken from the placenta. Again, the doctor goes in with a needle, either through the abdomen or through the cervix and grabs a few placenta cells… CVS is performed much earlier in the pregnancy, typically between ten and twelve weeks, before the end of the first trimester…

I pro e i contro del test invasivo…

… accuracy is, of course, the big plus of these tests relative to the screening. On the negative side is the possibility that the tests could cause a miscarriage. In principle, sticking needles into the uterus could certainly carry some danger…

Il “sentito dire” sui rischi di aborto…

… Common numbers are a 1 in 100 risk of miscarriage from CVS and 1 in 200 from amniocentesis…

Spoiler sui numeri reali…

… two conclusions. Firstly, the CVS test is transparently a better option than amniocentesis. Recent evidence shows that it carries the same risk of miscarriage and it can be done much earlier in pregnancy. Secondly, the risks from either of these procedures are much lower than 1 in 200. They are so low that it’s hard even to put a figure on it, but my best estimate was about 1 in 800…

Da dove arriva il “sentito dire”? Studi vecchi

… The 1 in 200 figure is based on a study from the 1970s that considered about 1,000 women who underwent amniocentesis and 1,000 matched controls…

Studi in cui non si controllava con l’età

… In the amniocentesis group, 3.5 percent of the women had a miscarriage. In the control group, it was 3.2 percent. This difference was not statistically significant and disappeared completely when corrected for maternal age….

Un altro studio sviante…

… a study in the 1980s that did a better job in various ways and suggested a similar risk. But even this study is hard to learn from, in large part because it is old.10 And, in fact, this “old study” problem is also likely responsible for the impression that CVS is riskier than amniocentesis. Old studies are not always useless. Some things do not change much over a period of 30 years. But some things do and the technology for doing these tests is definitely in that category…

Ma cos’è cambiato nel tempo? Molto…

… The biggest changes have to do with the use of ultrasound during these procedures. The most significant risk of these tests is that you accidentally hit the foetus with the needle; a related risk is the needle going through the placenta, which can also cause problems… Today, doctors typically watch what they are doing the entire time on the ultrasound….

Utile comparare i tassi di aborto spontaneo tra chi si sottopone a CVS e chi non fa nulla…

… What was the true risk if 1 in 200 was too high? The simplest way to figure this out is to compare miscarriage rates for women who have CVS to similar women who have no screening. There are very few studies like this. I did find one and it was very reassuring. It compared 5,000 women who had CVS to 5,000 women who did not.14 The authors found miscarriage rates of 3.3 percent for women who had no procedure and 2.7 percent for women who had the CVS…. Of course, there is no reason to think CVS would be protective; what this study demonstrates is that it is plausible that the risk from the procedure is very small, maybe even zero…

Amnio e CVS… rischi simili…

… One good one is the FASTER trial…. The chance of pregnancy loss before 24 weeks was 0.94 percent in the control (no amniocentesis) group and 1.0 percent in the treatment (amniocentesis) group. This difference is very small… Two other recent studies used a similar design, comparing women who had an amniocentesis to similar women who did not and found the same results…

Conclusioni…

… we can’t reject the claim that there is no increase in risk from the procedure. If we take the magnitude of their estimates seriously, they suggest a procedure-related risk between 1 in 600 and 1 in 800….

Riassuntino…

… The Bottom Line: Part 2 • Miscarriage risks from CVS and amniocentesis are indistinguishable, making the earlier-in-pregnancy CVS test the clear winner. • A reasonable estimate of procedure-related miscarriage risk from CVS is about 1 in 800 but . . . • . . . most studies are not large enough to allow us to reject the claim that there is no increased risk from this procedure…

***

Perché si raccomanda l’amnio sopra i 35?

Perché si ritiene che a quel punto il rischio di avere un down eguagli il rischio di aborto.

Problemi: 1) le probabilità conteggiate sono sbagliate (vengono da studi vecchissimi) 2) si assume che avere un down e perdere il bambino in grembo siano due mali simili: assurdo!…

… This recommendation assumes that everyone thinks that having a child with a chromosomal problem is exactly as bad as having a miscarriage. That’s the logic under which comparing the probabilities is enough. This cannot be correct; it might not even be correct for the average person and it’s certainly not correct for every person. It seems extremely likely that for some women and families, they would much prefer to have a child with Down’s syndrome than to lose a healthy baby….

Riassumiamo meglio la distorsione nelle raccomandazioni ufficiali…

… Let’s say you are 31. With a good result on the non-invasive screen, the baby’s risk of having Down’s syndrome is around 1 in 7,000. The risk of miscarriage from the CVS test is around 1 in 800. What you need to decide for yourself is whether having a baby with Down’s syndrome unexpectedly would be more than eight times worse than having a miscarriage. If yes, then do the CVS. If no, then stick with the non-invasive screen…

La decisione migliore forse è cominciare con la translucenza e aggiornare i rischi. Quasi sempre si raggiunge una soglia che ci fa evitare il CVS:

… We ultimately decided I would undergo the non-invasive screening. Yes, there would be some remaining risk, but it would be very small. The testing went well, we stopped there and Penelope was born healthy….

Il futuro: test a rischio zero…

… Of course, the absolute best of both worlds would be if you could get the baby’s DNA without going anywhere near the baby. Is this possible? It turns out yes. When you are pregnant, some of the baby’s DNA circulates in your bloodstream – this is called “cell-free foetal DNA”. If doctors could separate out the DNA that belongs to the baby from that which belongs to you, they could effectively “see” the baby’s DNA without seeing their cells…. science moves fast and when Penelope was about 18 months a newly pregnant friend called me up asking about a test called “MaterniT21” that does exactly this procedure…

 

 

 

Annunci

Rispondi

Inserisci i tuoi dati qui sotto o clicca su un'icona per effettuare l'accesso:

Logo WordPress.com

Stai commentando usando il tuo account WordPress.com. Chiudi sessione / Modifica )

Foto Twitter

Stai commentando usando il tuo account Twitter. Chiudi sessione / Modifica )

Foto di Facebook

Stai commentando usando il tuo account Facebook. Chiudi sessione / Modifica )

Google+ photo

Stai commentando usando il tuo account Google+. Chiudi sessione / Modifica )

Connessione a %s...