Screening ­ whose risk is it anyway?

Mothers-to-be now face a daunting array of antenatal tests. Often they cause anxiety. Sometimes they raise agonising choices. But is there an alternative?

Joanna Moorhead
Saturday 17 September 2011 14:09

Antenatal tests aren't new, but they are more controversial than ever. Twenty years ago, when the first ones were introduced, they were hailed as a medical breakthrough.

Antenatal tests aren't new, but they are more controversial than ever. Twenty years ago, when the first ones were introduced, they were hailed as a medical breakthrough. Today, among both health professionals and parents-to-be, the mood is more guarded. Tests can be useful ­ but only for some. They can be conclusive ­ but not all are. They can be the passport to a stress-free pregnancy ­ or a stress-filled one.

Now comes the latest research, from St Bartholomew's Hospital in London, which claims to show that for every Down's syndrome baby identified by amniocentesis, four healthy foetuses are miscarried. It's long been known that amniocentesis ­ a test in which a needle is inserted through the abdomen into the uterus to take a sample of amniotic fluid ­ carries a risk of miscarriage. That risk is usually put at about one in 100 ­ and given that 40,000 women have the test annually, and that for the vast majority the risk of Down's would be far lower than 1 per cent, it's clear that, overall, more babies are being lost than are being identified with the syndrome.

Is that, though, the relevant issue here? Antenatal testing, says Mary Newburn of the National Childbirth Trust, is a complex issue; each couple has to weigh up what level of risk of a disabled baby they're willing to take, based on how far they want to go to avoid that risk. "Some couples feel they simply couldn't bring a Down's baby into the world, and need to be absolutely sure their baby is clear: for them, the need to be certain may outweigh the risk of losing the child. Others ­ particularly, perhaps, women nearing the end of their reproductive lives, for whom another pregnancy may not happen easily ­ may be more willing to accept some level of risk," she says. For one woman, a risk factor of one in 250 may be easily dismissed; another will be kept awake at night by a one in 500 risk.

"Risk factors" have entered the language of pregnancy over the last couple of decades, but they're nothing new. A number of babies each year are born with any given disability, and all you need is a calculator to work out your risk of giving birth to one of them. If it's Down's, the risk rises with age, so you need to take that into account: at 25 you've a one in 1,500 chance of a Down's baby; at 35, one in 300; at 45, one in 30. It's all straightforward stuff.

What's less straightforward is that, thanks to advances in ultrasound and in blood-testing techniques, women in early pregnancy can now have tests that look for various "markers" that may (but only may) indicate a problem. These screening tests do not give a conclusive result, since they are only looking for indicators that there might be something wrong, but they are used to generate an individual "risk factor" based on all the known information.

This means that a woman who has an across-the-board, one in 300 risk at 35 can find, after a nuchal fold ultrasound scan to check for Down's, that her individual risk of Down's in this particular baby is hugely improved to one in 1,000; or it can mean a greater risk, of something like one in 200.

If the "risk factor" is deemed too worrying to live with, the only way to be certain is to go ahead with an invasive test that will give a proper diagnosis ­ but carries a risk of miscarriage.

Like everything else in life, antenatal screening has an upside and a downside. The upside is that people like my friend Sophie (who three years ago was pregnant with a much-wanted baby at 39, and who had previously suffered a miscarriage) get to hear that their risk of a baby with Down's is extremely low. In the absence of a screening programme, Sophie might have considered amniocentesis; an agonising choice given the miscarriage risk. Armed with the information from the ultrasound scan, she didn't give either Down's or amniocentesis another thought and had a baby unaffected by the syndrome.

The flip side is someone like another friend, Anne, who at 30 was jogging through her pregnancy without a care in the world when she was told, after her nuchal fold scan, that the marker in question ­ a sac of fluid behind the baby's neck ­ did indicate that there might be a problem, pushing her risk factor from about one in 800 to one in 250. Anne had gone to her scan expecting an exciting opportunity to see her baby for the first time; she had not imagined she'd be given "bad news".

She was devastated: she told me later that she felt as though her much-looked-forward-to pregnancy was suddenly "on hold". She had planned to go to work after her scan, armed with the traditional blurry image of a waving foetus; instead, she went home in tears and didn't go back to work for a month. She worried herself sick over whether to have an amniocentesis, and eventually decided to do so ­ partly because she realised she couldn't live with the stress of not knowing, now that a question mark had been put into her mind.

The test was carried out when she was 16 weeks pregnant ­ she could feel the baby kicking ­ and came through two weeks later. It was negative. The relief was immense, but Anne started to feel desperately cheated. She'd believed all was fine with her pregnancy, and medicine questioned that. "I went through hell in those weeks ­ I was scared, I was crying all the time, I certainly couldn't carry on my normal life or go to work," she says. "Even when it was over, it wasn't over, because I didn't really feel safe about being pregnant again. And I think it affected how I felt about the baby, because I was trying to shut her out rather than look forward to her coming."

Anne's story shows there are two vital issues in antenatal testing, and a lot more work needs to be done on each. The first is giving better information to women before they begin the screening process; the second is about improving screening to the extent that the net is drawn more tightly around those women who are "at risk" of a disabled baby, so that as few as possible go through an amniocentesis needlessly.

"One of the problems is that so much screening is presented as 'routine'," says Mary Newburn. "Nuchal fold screening, or blood serum screening that looks for 'markers' in a sample of the mother's blood, don't carry any risks to the baby, so it's sometimes taken as read that women will want to have them, that they're part and parcel of antenatal care. But in fact, by having those initial screening tests, you are getting embroiled in something that may lead to you having an amniocentesis or chorionic villus sampling, another invasive test with a miscarriage risk."

Another area is the fact that, while a screening result may be reassuring, it doesn't rule a condition out altogether. "Many women who've had a low-risk result go ahead with a pregnancy utterly convinced their baby is fine," says Mary Newburn. "For a very small minority, that won't be the case, and they may be absolutely devastated, and find it very hard to cope, when they give birth to a Down's baby despite being told the chances were one in 2,000."

Helen Statham, of the support group Antenatal Results and Choices, says she believes pregnant women often hear what they want to hear. "There's this ethos that these tests are for reassurance, but if you go in with that attitude, you're not focusing on the fact that your baby is being checked and that there might be a question raised over its health," she says.

On the second issue ­ improving screening so the net is drawn tighter around the "at risk" group ­ work continues. Reports that a blood test is about to be launched that may eventually be able to diagnose Down's from a maternal blood sample are, says Ms Statham, premature; the breakthrough is probably not going to come this year or next. However, amniocentesis ­ which until now has meant an agonising two-week wait for results ­ is now being processed in some centres in two days.

What Ms Statham feels most strongly about is the myth that pregnant women are all seeking the "designer baby", and make decisions lightly on what to do about the information now available on the health of their unborn child. "Our experience is that few make a decision easily. They often tell us it's the most difficult dilemma they've faced in their lives, more difficult than anything they expect in the future."

The Antenatal Results and Choices helpline is: 020-7631 0285

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