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Dead certainty

MagazineOctober 1991 (Vol. 2 Issue 7)Dead certainty

The biggest risk you may face of having a deformed or retarded child could be when taking the prenatal diagnostic tests themselves

The biggest risk you may face of having a deformed or retarded child could be when taking the prenatal diagnostic tests themselves.

I know this sounds like every new mother you've ever spoken to, but my kid is some smart cookie. Yet according to medical science, my 21 month old daughter Caitlin should have had Down's Syndrome. If I had listened to the experts I might have aborted her or lost her through a high tech test induced miscarriage. The very thought sends a chill right down my spine.When I got pregnant, I firmly resisted all recommendations to have ultrasound monitoring and amniocentesis despite being a particularly elderly primagravida (37) at conception, because of my fears about their known and unknown risks. Nevertheless, when I was 16 weeks pregnant, my doctor was particularly persuasive about my taking a routine prenatal alpha fetoprotein (AFP) test. The test measures the level of AFP produced by the foetus and present in the mother's bloodstream. It was designed to detect babies with rare neural tube defects like spina bifida, as evidenced by a "high" reading. Although the test wasn't designed for it, low readings are now thought to be associated with an increased risk of Down's Syndrome.

"Just to put your mind at rest," my doctor cajoled.

Since it only involved taking a blood sample from my upper arm rather than invading the womb as all other prenatal tests do, I let myself be talked into it. After all, I was having a fantastic pregnancy. Of course my baby was perfectly healthy. Now I'd know for sure. What was there to lose?

A week or so later, my doctor's secretary phoned and said he needed to speak to me. "What for? Did the test come back?" I asked apprehensively. "That's what he wants to discuss with you."

For an agonizing half hour I sweated on the phone while waiting for him to get on the line. When he did, it was to report the words I'd never even thought to consider: "The results of the AFP test are borderline low."

I burst out sobbing and only after five minutes had calmed down sufficiently to ask what I already knew that meant.

"There's a slight possibility of Down's Syndrome."

I don't remember much of the rest of the conversation. My doctor tried a few gentle reassurances we could find out for sure through a combination of amniocentesis and ultrasound; this combination of tests had a high degree of accuracy; the other borderline situations he'd investigated had turned out all right.

Finally I managed to say that I would call him back. I had some secretary drag my husband out of a meeting to tell him the news and after he rushed home we considered our options. We could run through the battery of tests with ultrasound and amniocentesis, and risk miscarrying a perfectly healthy baby or damaging it through the test both known risks of the procedure. We then discussed the ramifications of a test result confirming that I was carrying a handicapped child. We would be faced with the decision of aborting a five month old foetus not some lima bean sized tadpole, but a perfectly formed, nearly viable human being. It meant going through labour and giving birth to a dead baby or, if he wasn't expelled in that manner, having the body removed, piece by piece. I looked down at my bump. For me, that simply was not a possibility I could ever contemplate, no matter how deformed this child might be, which then made the entire AFP exercise an utter waste of time. If you are not prepared to abort a handicapped foetus, there is no point in going through the tests.

I hated medicine at that moment for creating a situation that could only be resolved through the high tech measures I had so wished to avoid. If I had never had the AFP test, I thought, I would never have to consider subjecting the baby to a battery of possibly damaging tests just to bury the doubts raised by the first test.

In the end, to our minds, there was only one reasonable path: to ignore the test and to listen to our hearts, which told us that the result was wrong.

This is what we chose to do. I called my doctor to tell him, and my husband and I never spoke about the test again. Sure enough, at the end of my term, out came a perfectly normal, healthy baby.

After my own experience, I heard of at least three friends or acquaintances with false positive AFP readings. And now prenatal tests are in the news again. A recent large scale study on chorion villus sampling the supposedly early Down's Syndrome test has raised many serious questions about the procedure, at the same time that the University of Medicine at Leeds has announced a new "triple test" to replace maternal age as the sole determinant for women at risk of giving birth to a Down's Syndrome baby. As usual, medicine decries one invasive technique while placing its hope and confidence in another, equally error prone procedure.

And this is despite the fact that none of these whizzy screening tests seems to be making much difference. The amazing fact is that despite the 30,000 amniocenteses and 3,000 CVS tests performed each year in the UK, less than 20 per cent of Down's babies are detected. This may have something to do with the fact that 70 per cent are born to younger mothers who don't have the tests a fact that tends to pour water on the idea that Down's Syndrome is a result of elderly parenthood. Here, then, are the up to date problems with the three main prenatal diagnostic tests: AFP, chorion villus sampling and amniocentesis. It may convince all you other, so called elderly mothers to be that the most substantial risks you face of deformed or retarded children may result from the diagnostic tests themselves.

AFP Tests

There is no doubt that the batting average on this test is appalling. According to Helen Klein Ross in last summer's issue of Mothering, there is a 3-4 per cent error rate in abnormally high readings on first screening. "This means that of every 2,000 women tested," she says, "100 will have an abnormal reading, but only 1 or 2 will be carrying a foetus with this congenital defect."

Even so high a miss record as this could be conservative. In Planning for a Healthy Baby, Foresight founder Belinda Barnes cites a 1982 British Medical Journal article (Harris et al) estimating a failure rate of 20 per cent.

According to Dr Robert Mendelsohn, the test has false negatives too, as evidenced in a Lancet article (September 27, 1986) concerning two babies born with spinal defects whose mothers nevertheless had normal AFP readings.

Ms Ross points out that the AFP test "misses about 40 per cent of spina bifida cases, 10 percent of anencephaly cases and 80 per cent of foetuses with Down's. All of which makes a negative result by no means reassuring."

Twins or a miscalculation about the date of conception are two common ways that test results are thrown off. In my case, we were sure about the dates, but Caitlin was born 28 days past her estimated due date (first babies who are not induced are very often late). As a slow grower, she probably deviated sufficiently from the norm to show up as "abnormal".

In other words, mostly what this test produces is a good deal of needless anxiety, which can only be dispelled by subjecting the foetus to amniocentesis or ultrasound, two procedures with their own potential risks. (See WDDTY Vol 1 No 6 for the known and suspected risks of foetal ultrasound scans.) Indeed, as Ms Ross put it, for anyone younger than about 39, the risk of losing a healthy baby through amniocentesis (about 1 in 200) is greater than the risk of having a baby with Down's Syndrome.

Chorion Villus Sampling

This was supposed to be the answer to every older mother to be's prayers. Although amniocentesis was already well established to detect Down's Syndrome, the trouble, as we noted, is that one has the test so far down the line, at 16 weeks pregnant, with two or three weeks more before results are available. If the test shows an abnormality, and you do not wish to continue you must undergo a second trimester abortion, with all the physical and psychological ramifications.

With this test a tiny sample of the tissue of the "villi", the hairlike projections of the chorion (the sac containing the embryo in the uterus, which becomes the placenta), taken between the ninth and 12th week of pregnancy is supposed to tell you the genetic typing of the foetus. This could help to screen for Down's Syndrome, as well as sickle cell anaemia, muscular dystrophy and sex linked abnormalities. The villus sample is taken with a needle inserted transabdominally (through the walls of the abdomen) or transcervically (through the vagina).

A resent study, conducted by the Medical Research Council, of over 3,000 women from seven different European countries, compared the results of pregnancies of women who'd had CVS with those who'd had amniocentesis.

With CVS, women are more likely to lose their babies. Only 86 per cent of the women in the CVS group had successful pregnancies, compared to 91 per cent in the amniocentesis group. This was due to a greater number of foetal deaths before 28 weeks, a higher number of terminations of supposed abnormalities and a higher number of neonatal deaths, largely due to a higher number of premature babies born before 32 weeks.

"The results of this trial suggest that the policy of chorion villus sampling in the first trimester reduces the chances of a successful pregnancy outcome by 4.6 per cent," concluded the MRC.

Although the study couldn't tell for sure how many of the CVS tests were false positives because not all aborted or miscarried foetuses were tested, they did find three false positives, one in the CVS sample and two in the amniocentesis group, and one false negative with CVS. Two other CVS cases were thought to be false positives.

The genetic material found in the chorion villus may not be identical to that of the foetus, leading to false positives or negatives. In the MRC study and elsewhere, researchers have found that samples of the chorion contained abnormal chromosomes, but that the babies resulting were nevertheless normal. In a letter to The Lancet (18 May 1991), two doctors from Copenhagen reported such an instance; the woman went ahead and terminated what turned out to be a normal baby.

What this means, of course, is that the chorion membrane itself could have a defect not shared by the foetus, possibly resulting from a twin that had died and been reabsorbed. Or, that abnormal placental tissue in these early stages doesn't mean anything in the long term.

In other words, the entire theory upon which CVS rests that chorion villus will tell you about the state of the foetus could be wrong.

There are many reports of limb abnormalities of babies whose mothers had CVS. In The Lancet (March 30, 1991) Firth et al report five cases abnormally small or deformed limbs among 289 pregnancies which had been investigated by CVS at 55-66 weeks gestation. Several other researchers followed that story with similar results. In one, Italian researchers from Catholic University in Rome examined 118 cases of limb defects in babies born between 1988-90 in Italy and found that four were born to mothers who'd had CVS. "Our findings suggest an increased risk for transverse limb reduction defect associated with CVS at any gestation age and an exposure attributable risk of 1 in 200," they wrote. This compares to an ordinary risk of 1 in 3100 among the population at large. The risk of deformities from CVS would be even greater if other malformations besides limb reductions were considered, they said.

What seems evident is that the villi isn't as dispensable as medicine believed, or that there is a high risk of damage. Many are investigating whether mothers are at higher risk when having the test done before 56-66 days gestation.

Because of the questionable accuracy of CVS, you might have to have amniocentesis to confirm its results, thus subjecting your baby to two major insults and multiplying your risk of miscarriage. The risk of losing a baby through CVS has now been put at nearly five per cent. When you add amniocentesis on top of that, you start moving up to a very substantial miscarriage risk.


By far the preferred test for Down's Syndrome and other genetic abnormalities, amniocentesis involves having a needle (guided by ultrasound) inserted into your abdomen and uterus and drawing out amniotic fluid. These cells are then cultured for a few weeks and the chromosomes examined, which explains the three week delay between the test and its results.

The risks of miscarriage are assumed to be l to 1.5 per 100 pregnancies, largely from damage caused by the needle or the introduction of infections. In 1978, the Medical Research Council also reported a 3 per cent increase of neonatal respiratory distress, and a 2.4 increase of congenital dislocations of the hip or club feet. The high miscarriage rate is worth keeping in mind if you are older, since there's no guarantee you'll get pregnant again.

There are also plenty of false positives even with this supposedly highly accurate test. Anyone doubting that any of this could happen to them should have a look at the heartbreaking story of an anonymous woman doctor in the British Medical Journal (20 April 1991) who'd suffered two miscarriages due to toxoplasmosis and was then referred for "cordocentesis", examination of the placental cord at 20 weeks. After the asiration needle was inserted, she wrote, "My baby began to thrash around beneath the stabbing needle, hitting out with his tiny hands. . . A cascade of grey started to fall from the cord. It must have been blood. I voiced my fears but was told that it was just amniotic debris."

A scan later that day showed a large blood clot within the amniotic sac. The following morning, the woman underwent another scan. "The picture was still, lifeless. I prayed he was just sleeping. The probe moved and found the foetal heart. It too was silent." Doctors induced labour in a few days. The woman gave birth to a stillborn, perfectly normal baby boy.

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