Brandenburg, H. (Helen)

Cohen-Overbeek, T.E. (Titia)

Jahoda, M.J. (M.)

Los, F.J.

Erasmus University Digital Repository

LETTERS TO THE EDITOR 387 mothers of twins unnecessarily; the positive predic- tive value of a Down’s screen in a singleton pregnancy is low (Reynolds et al., 1993) and would probably be lower in a twin pregnancy because the difference between affected and normal pregnancies will be smaller. T. M. REYNOLDS Clinical Chemistry Department, Burton Hospitals NHS Trust, Burton Hospital, Belvedere Road, Burton-upon-Trent, DE13 O R B ,  U. K. REFERENCES Reynolds, T., Nix, B., Dunstan, F., Dawson A. (1993). Age related detection rates in Down screening: an aid to counselling, Obstet. Gynecol., 81,447450. Royal College of Obstetricians and Gynaecologists (1993). Report of the RCOG Working Party on Biochemical Markers and the Detection of Down’s Syndrome, RCOG: London. Wald, N., Densem, J. (1994). Maternal serum free 8-human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down’s syndrome, Prenat. Diagn., 14, 319-330. AUTHOR’S REPLY We have considerable sympathy with your correspondent’s opinion. Screening twin pregnan- cies poses special problems-in interpretation, diagnosis, and if one twin were affected, what action to take. The discovery of a twin pregnancy can reasonably be taken as an indication to avoid screening. The purpose of our publications on the serum levels in twin pregnancies was not to encourage the screening of twin Pregnancies, but to enable a report to be issued if a screening test were per- formed. Once a laboratory has tested a sample, it is usually unacceptable not to interpret it at all. Both the doctor and the patient will want an answer. The test, interpreted as we proposed in our paper (Wald and Densem, 1994), will identify about 5 per cent of unaffected twin preg- nancies as screen-positive, but with an uncertain detection rate. This problem is probably best dealt with by routinely performing a dating scan before the serum screening test. This will identify a twin pregnancy so that if screening in a twin pregnancy is not wanted, it can be avoided and will also improve the performance of screening in singleton pregnancies (Wald and Kennard, 1993; Wald et al., 1994). N. J. WALD, J. W. DENSEM ANDA. KENNARD Department of Environmental and Preventive Medicine, Worf on Institute of Preventive Medicine, St Bartholomew’s Hospital Medical College, Charterhouse Square, London E C l M 6 B Q ,  U.K. REFERENCES Wald, N.J., Densem, J.W. (1994). Maternal serum free 8-human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down’s syndrome, Prenat. Diagn., 14, 319-320. Wald, N.J., Kennard, A. (1993). The value of perform- ing a dating scan on all women in antenatal screening for Down’s syndrome and neural tube defects, Ultra- sound Obstet. Gynecol., 3, 3-5. Wald, N.J., Densem, J.W., Smith, D., Klee, G.G. (1 994). Four-marker serum screening for Down’s syndrome, Prenat. Diagn., 14, 707-716. Transabdominal chorionic villus sampling and bowel loops as a restricting factor Since 1987, the vast majority of chorionic villus sampling (CVS) in our department has been done via the transabdominal (TA) route, because of the advantages over the transcervical (TC) way, as has been described earlier (Jahoda et al., 1987, 1990; Monni et al., 1988, Brandenburg, 1992). However, 388 LETTERS TO THE EDITOR Table I-TA-CVS procedures postponed because of bowel loops between the uterus and abdominal wall n % Scheduled for TA-CVS 978 TA-CVS at first attempt 893 91.3 Postponed 85 8-7 TA-CVS at second attempt 26 2.7 Amniocentesis 57 5.8 Total TA-CVS 919 94.0 No procedure 2 0.2 a problem occasionally encountered at TA-CVS is the presence of bowel loops between the uterus and the abdominal wall, which is a contraindication for an invasive procedure. Whenever bowel loops are found to be present, patients are rescheduled for the following week. Between 1 January 1993 and 1 January 1994, 978 patients were scheduled for TA-CVS at 11.3- 12.6 weeks (mean 12-0 weeks). Eighty-five women of this group were postponed for a week because loops of intestine were present between the uterus and the abdominal wall during the pre-procedure scan. The gestational age of this group was not different from the group that underwent TA-CVS at the scheduled time. After this week, 26 women underwent TA-CVS (at 12.3-135 weeks, mean 13.1 weeks) and 57 were rescheduled for amnio- centesis around 16 weeks. Two women decided against further intervention (Table I). Although TA-CVS offers many advantages over TC-CVS in terms of lower fetal loss (0.9 per cent up to 28 weeks during this same period), no need for a full bladder, a less embarrassing position for the woman, and a faster and easier procedure, there are also some disadvantages. One of them is the somewhat later time of sampling that some- times leads to a less easy termination of pregnancy on an outpatient basis or even to a clinical prosta- glandin termination. The other disadvantage is the above-mentioned problem of bowel loops between the uterus and the abdominal wall. For most women who are mentally prepared for a prenatal diagnostic procedure, it is very distressing to be sent home for a week because ‘the bowels were in the way’. To prepare women for this possible event we point out this problem to them especially when at the initial visit the uterus is retroverted and can only be scanned transvaginally. Since 94 per cent of the women who were scheduled for TA-CVS indeed underwent the procedure and only 0-2 per cent decided against any procedure, there seems to be no need to change our policy. H. BRANDENBURG*, T. E. COHEN-~VERBEEK*, F. J. Lost AND M. J. JAHODA* Departments of *Obstetrics and Gynaecology and TClinicaI Genetics, Academic Hospital Dijkzigt Dr Molewaterplein 40 3015 GD Rotterdam, The Netherlancis REFERENCES Brandenburg, H. (1992). Prenatal diagnosis in women of advanced maternal age, Academic thesis, Rotterdam. Jahoda, M.G.J., Pijpers, L., Vosters, R.P.L., Wladimiroff, J.W., Reuss, A., Sachs, E.S. (1987). Role of maternal age in assessment of risk of abortion after prenatal diagnosis during first trimester, Br. Med J., 295, 1237. Jahoda, M.G.J., Pijpers, L., Reuss, A., Brandenburg, H., Cohen-Overbeek, T.E., Los, F.J., Sachs, E.S., Wladimiroff, J.W. (1990). Transabdominal villus sam- pling in early second trimester: a safe sampling method for women of advanced age, Prenat. Dhgn., Monni, G., Olla, G., Cao, A. (1988). Patients’ choice between transcervical and transabdominal chorion vil lus sampling, Lancet, ii, 1057. 10, 307-3 1 1 .  ‘Faint-positive’ or ‘false-positive’ amniotic fluid acetylcholinesterase. A diagnostic dilemma Positive acetylcholinesterase (AChE) in amniotic fluid (AF) has been associated with neural tube defects (NTDs) for a long time (Collaborative AChE Study report, 1981). A positive AChE result was defined as the appearance of an unambiguous large band in the electrophoretic gel at the position of A C E  from cerebrospinal fluid which is inhib- ited by means of the specific inhibitor BW 284 C51. 

Transabdominal chorionic villus sampling and bowel loops as a restricting factor [3]

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