‘triple test’ analyses the levels of three substances in the mother’s blood: unconjugated oestriol, total human chorionic gonadotrophin and AFP; low levels of oestriol, high levels of HCG and low levels of AFP are considered the first indication of the possibility that the mother is carrying a baby with Down’s syndrome. These measured levels, plus the mother’s age and genetic history, are thrown into some mathematical stew in order to determine her personal odds of having a Down’s baby. The test is supposed to be a better marker than age alone for determining whether a woman should go on to have amniocentesis, which more accurately determines whether a child has Down’s syndrome. At best, the triple test detects 70 per cent of Down’s babies in women over 35, and only 50 per cent in women younger than this.56
All those who receive a positive triple test result must wait five or six anguished weeks before receiving the results of the recommended amniocentesis to confirm or deny the suspicious results of the first test. If you are one of the unlucky ones who receives a false-positive, and a large percentage now do,57 you will needlessly undergo amniocentesis, which increases the risk of miscarriage from 3 to 4 per cent. In other words, one out of every 100 women with a false-positive triple test opting for amniocentesis may abort a normal baby.
CHORIONIC VILLUS SAMPLING
Chorionic villus sampling (CVS) was supposed to be the answer to every older mother-to-be’s prayers. Although amniocentesis is well established as a test to detect Down’s syndrome, you have to wait to have the test until your sixteenth week of pregnancy, then wait 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, which entails, in effect, giving birth to a dead 20-week-old foetus, with all the physical and psychological ramifications that entails.
Then in the early seventies some medics from Sweden and the Far East figured out that you could take a tiny sample of the tissue of the ‘villi’, the hair-like projections of the chorion (the sac containing the embryo in the uterus, which becomes the placenta) between the 9th and 12th week of pregnancy and it would 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).
Lately, a number of concerns about chorionic villus sampling have finally been confirmed by several large-scale studies. The latest, conducted by the Medical Research Council, of over 3,000 women from seven different European countries, examined the results of pregnancies of women who’d had CVS against those who’d had amniocentesis.58
Compared with women undergoing amniocentesis, those who elect CVS were 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.
CVS can cause massive loss of blood from the womb, which may lead to the death of the foetus. This discovery from the Erasmus University in Bilthoven, the Netherlands, counters an earlier view that the foetus could survive such a loss of blood.59
‘The results of this trial suggest that the policy of chorionic villus sampling in the first trimester reduces the chances of a successful pregnancy outcome by 4.6 per cent,’ concluded the MRC report.60
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. However, the researchers did find three false-positives, one in the CVS sample and two in the amniocentesis group, and one false-negative with CVS. Two other cases in the CVS group were thought to be false-positives.
False-positives and -negatives are potentially common because the genetic material found in the chorionic villus may not be identical to that of the foetus. In the MRC study and elsewhere, samples of the chorionic villus were found to contain abnormal chromosomes, but the babies resulting were nevertheless normal. Two doctors from Copenhagen reported such an instance; the woman went ahead and terminated what turned out to be a normal baby.61
In another case in Brest, France, CVS carried out on a foetus showed the chromosome linked to cystic fibrosis was present. Despite the test results, the parents decided to proceed with the pregnancy and the mother gave birth to a healthy baby girl. The doctor who reported the case estimates the chances of such a false-positive are one in six.62
What this means, of course, is that the chorionic membrane itself could have a defect not shared by the foetus, possibly resulting from a twin that has died and been reabsorbed. Or, it could mean that abnormal placental tissue in these early stages doesn’t mean anything in the long term (the placenta of the Copenhagen case showed normal cultures on biopsy after the abortion). In other words, the entire theory upon which CVS rests – that chorionic villus will tell you about the state of the foetus – could be wrong.
Reports have now flooded in of limb abnormalities among babies whose mothers had CVS. At the Churchill Hospital in Oxford, five cases of limb-reduction defects (where arms or legs are abnormally short) occurred among nearly 300 pregnancies which had been investigated by CVS at 55 to 66 days of pregnancy.63
Italian researchers from Catholic University in Rome found that four of the 118 cases of ‘transverse’ limb reductions born between 1988 and 1990 in Italy occurred among babies born to mothers who’d had CVS.64
From their own data, they reckoned the risk of these deformities occurring for mothers given CVS at any point in the pregnancy was 1 in 200. This compares with an ordinary risk of 1 in 3,100 among the population at large. The risk of deformities from CVS would be even greater if other malformations besides limb reductions were considered. In one study of mothers given CVS, all 75 had produced a baby with some birth defect, from lost limbs to damaged nails.65
Far from being less invasive, the earlier the CVS was given, the more severe the abnormality. The greatest deformities occur among foetuses given CVS 56 days after conception.66
It’s believed that vascular disruption or puncture of the amniotic sac might have something to do with producing the deformities. Whatever the damage results from, it’s clear that the tiny villi aren’t quite as dispensable as medicine once believed.
The US Centers for Disease Control and Prevention now recommends that doctors warn parents of the risk of CVS causing limb defects to their babies at least up to 76 days’ (nearly 11 weeks’) gestation. The CDC also warns that testing can be dangerous in foetuses older than nine weeks – assumed in the past to be the safest period.
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 5 per cent.
