SCREENING FOR NEURAL-TUBE DEFECTS

SCREENING FOR NEURAL-TUBE DEFECTS

600 SCREENING FOR NEURAL-TUBE DEFECTS SiR,—The DHSS Working Group on Screening for Neuraltube Defects’ has recently produced its report. Among its re...

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600 SCREENING FOR NEURAL-TUBE DEFECTS

SiR,—The DHSS Working Group on Screening for Neuraltube Defects’ has recently produced its report. Among its recommendations is one that maternal serum alpha-fetoprotein (AFP) assays "should be performed only in laboratories with a large workload (for example 400 assays per week, with extension to 800 assays per week in emergency)". We disagree that such a large workload is necessary, or that a workload of "less than 100 per week can be dangerous". The working group felt that smaller workloads would lead to technical deficiencies and difficulties in the construction of normal ranges. This is not borne out in practice; satisfactory results have been obtained from laboratories with smaller workloads, and the results from some have been published"* Certainly a workload can be too small, although a lower limit is hard to define. An international workshop sponsored by the U.S. National Institute of Child Health and Human Development, which met in 1978, concluded that a reasonable minimum workload would be tests on 50 women per week. Moreover there are disadvantages in performing AFP assays on a large scale5 and the size of workload is probably best judged in relation to local conditions. The DHSS report also states that a screening laboratory "must possess considerable expertise in radioimmunoassay of AFP, best demonstrated by acceptable performance in the external national quality control scheme for this assay over a period of at least six months before a full screening service is offered". This is, in our view, an unreasonable recommendation since there is no evidence to show that laboratories that participate in centrally organised AFP quality-control schemes achieve, as a result, a lower screening false-positive rate and higher detection rate than those which do not. There is also no general agreement regarding the criteria by which assay performance should be assessed, and if participation is linked to the use of recommended standards, reagents, or technical procedures this may restrict development. If central quality-control schemes are to be compulsory a case needs to be made that the benefits are likely to outweigh the disadvantages. I.C.R.F. Cancer Epidemiology and Clinical Trials Unit, Radcliffe Infirmary, Oxford

Department of Human Genetics, Western General Hospital,

Edinburgh

HOWARD CUCKLE NICHOLAS WALD

DAVID BROCK

SIR,-Pregnant women confronted with the information serum a-fetoprotein (AFP) is raised are bound to experience acute anxiety. At the same time they have to decide whether to agree to abortion should fetal abnormality be confirmed, and whether to permit their infant to be exposed to the risks of diagnostic amniocentesis, estimated by a Medical Research Council study6 to include an increased fetal loss of 1-1-5% and a similar increase in certain types of major infant morbidity. Against this background the Working Group on Screening for Neural Tube Defects’ firm recommendation that women should be counselled fully and given the chance to opt that their

programme before blood is taken, is to be The practice of putting the onus on the patient to opt out of the scheme and of only fully counselling her after the serum AFP level has been found to be raised, can surely no longer be condoned. The cautious approach of the working group to any rapid expansion of the screening programme is also wise. Much information is still required if we are to assess properly the advantages, disadvantages, and costs of screening. Furthermore, the data base on which many current estimates have been made continues to change rapidly in two ways. First, the natural incidence of CNS malformations appears to have been declining in the U.K., and elsewhere, since the 1950s. Between 1973 and 1978 alone there was a 22% decline in the notification rate in the U.K. The explanation may lie in improved nutrition. Indeed, if the exciting observations by Professor Smithells and his colleagues (Feb. 16, p. 339) on the prevention of neural tube defects by periconceptional vitamin supplementation are confirmed then spina bifida may largely become a disease of the past and make prenatal screening for this condition unnecessary. The second important change taking place during the last decade has been the development of a more conservative medical and approach to the management of the severely handicapped child at birth. Thus, the working group’s report reveals that while 50% of infants born alive with CNS anomalies in 1969 were still living at the age of 5, the figure for the 3-year survival of infants born in 1975 was only 30%. An unpublished survey of five English counties in 1977 revealed that the proportion of survivors among the infants with severe handicap due to open spina bifida was actually very considerably smaller. These two trends continue to reduce the potential benefit of prenatal screening and make the associated risks and anxieties less acceptable. In discussing the financial implications of a national screening programme, the report is on less sure ground. For example, the cost of a mother’s extra visit to the antenatal clinic for counselling and blood testing is rated at a mere 63 p. Nor is there any mention of the cost of examining any available amniotic fluid for chromosomal disorders. Surely, it would be unethical not to do so, especially after the fetus had been exposed to the risks of amniocentesis? Considerations such as these take on greater significance in the light of the D.H.S.S. health notice HN(79)116 warning that no additional resources will be made available for any developments in the screening programme. I would like to end with a plea that, in future, monitoring the outcome of screening studies should not only be concerned with the incidence of neural tube defects and their detection but also should investigate the impact that the programme has had on the mothers themselves, especially those unfortunate enough to have had raised serum AFP levels. I know of women who have found the news that their level was high and the period of uncertainty that followed so harrowing, that they have vowed never to be screened again. How common is this into the

screening warmly welcomed.



surgical

sort

of experience?

Department of Child Health, University of Bristol, Southmead Hospital, Bristol BS10 5NB

PETER M. DUNN

1.

Report by the Working Group on Screening for Neural Tube Defects. London: Department of Health and Social Security, 1979. 2. Brock DJH, Scrimgeour JB, Steven J, Barron L, Watt M. Maternal plasma alpha-fetoprotein screening for fetal neural-tube defects. Br J Obstet Gynœcol 1978; 85: 575 3. Wald NJ, Cuckle HS, Boreham J, et al. Antenatal screening in Oxford for fetal neural-tube defects. Br J Obstet Gynœcol 1979; 86: 91-100. 4. Woolfson J, Holt EM, Whyman AE, Mabbs DV. Maternal serum alpha-fetoprotein screening in a provincial Health District. Brit J Obstet Gynœcol 1979, 86: 87-90. 5. Brock DJH, Wald NJ, Cuckle H. Organisation of maternal serum-&agr;-fetoprotem screening for fetal neural-tube defects. Lancet 1977; i: 700. 6. Medical Research Council Working Party on Amniocentesis. An assessment of the hazards of amniocentesis. Br J Obstet Gynœcol 1978; 85: suppl 2, 1-41.

VANCOUVER WOES

SIR,-The desolateduet from Glasgow (March 1, p. 486) must have touched the hearts of all authors; but a doughty fighter like Professor Lennox can cleave a way for his secretary through "a coterie of clinical editors",9 B.C., CiBa, or ELSE. Wilkins J. Congenital malformations in Europe in war and peace. Health Trends 1976; 8: 21. 8. Note. Declining incidence of CNS malformations. Lancet 1979; ii: 1387. 9. O’Connor M. Typing reference lists. Lancet 1978; ii: 1373.

7. Rogers SC,