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Notes: Objective To investigate births with neural tube defects at a time when most districts were screening for the condition. The objective was to document the circumstances surrounding each affected birth and assess the care provided against given standards.Design Retrospective review of antenatal casenotes by the obstetric team.Population Three hundred and eight births in England and Wales in 1990 to 1991 were reported to the Office of Population Census Survey (OPCS) to involve neural tube defects. Sufficient information was available to identify both the woman and the obstetrician in 213 pregnancies. Details were obtained from a questionnaire completed by the obstetric team for 168 (79%). In 20/168 cases either the reported outcome was not a live birth/stillbirth or the pregnancy did not involve a neural tube defect: eight resulted in a ‘normal’ infant, eight were terminated and in four the abnormality was not a neural tube defect. Thus 148 eligible cases were available for analysis.Results Of the 148 births, the anomaly was not detected prenatally or detected later than 25 weeks of gestation in 98 cases (66%), diagnosed in a multiple pregnancy in 24 (16%) and diagnosed prenatally but the woman chose to continue the pregnancy in 26 (18%). Of the 98 births not detected prenatally or detected late during pregnancy, the surrounding circumstances were that screening was declined in six cases (4%), screening was not offered due to late booking in 30 (20%), serum alpha-fetopro-tein screening gave a false negative result in eight (5%), ultrasound screening gave a false negative result in 29 (20%), both screening methods gave false negative results in 17 (11%) and other reasons in eight (5%). The estimated sensitivity of ultrasound screening for anencephaly was 100%. For spina bifida the estimated sensitivity for singleton pregnancies is higher for serum alpha-fetoprotein screening, 84% to 92%, than ultrasound screening, 70% to 84%, for a range of assumptions regarding the degree of under-reporting to OPCS of live births and terminations.Conclusions Late booking precluded the offer of screening tests in a substantial proportion (22%) of cases. The presence of multiple fetuses including one or more with a neural tube defect was a serious additional complication in prenatal screening, diagnosis and counselling. Screening for neural tube defects was widespread in 1990 to 1991, although variations in the services provided were documented. Ultrasound scanning was a major component but was associated with a lower sensitivity than maternal serum alpha-fetoprotein screening for neural tube defects other than anencephaly.

Notes: Objective To examine access to and provision of prenatal genetic services relating to Down's syndrome.Design Retrospective review of obstetric casenotes.Sample Pregnancies involving Down's syndrome in England and Wales in 1990–1991 in women aged 38 or over. Information was obtained in 430 cases from a questionnaire completed by the obstetric team who were asked to provide details based only on documentation in the antenatal casenotes. The outcome of pregnancy was a termination in 268 (62%) cases, a liveborn child with Down's syndrome in 144(34%), a stillbirth in 9(2%), a miscarriage in 8(2%) and in one case was not known.Results Overall, prenatal diagnosis was not offered in 7% pregnancies (95% CI: 4.4–9.2%) with late booking given as the main reason. Of women offered prenatal diagnosis, 76% accepted (95% CI: 72.3–80.6%). Counselling was documented before prenatal diagnosis in 89% of cases (95% CI: 86.0–92.3%) and after the procedure, to discuss the results, in 73% (95% CI: 67.5–77.7%). In 10% of pregnancies terminated for Down's syndrome, fetal products were not sent to the laboratory. There was no report of a normal fetus having been terminated as a consequence of incorrect prenatal diagnosis. However, in 10% (95% CI: 5.9 to 14.0%) of cases examined in the laboratory, the diagnosis of Down's syndrome could not be confirmed. Details of prenatal diagnosis were not provided in five cases where a child with Down's syndrome was born. Of the remaining 139 livebirths, prenatal diagnosis was not offered in 27 (19%) cases, offered and declined in 92 (66%) and accepted in 20 (14%). In two cases a normal fetal karyotype was reported following prenatal diagnosis.Conclusions The study has demonstrated that in 1990–1991: 1. There were certain shortcomings in the documentation of antenatal care; 2. Late booking was the main factor precluding the offer of prenatal diagnosis to women aged 38 or over, and 3. The rate of confirmation of Down's syndrome in terminated fetuses was incomplete.

Notes: Quantitative trait loci (QTLs) for black-point resistance have been mapped in two doubled haploid-derived wheat populations, each thought to contain unrelated sources of resistance. In the ‘Sunco’בTasman’-derived population, QTLs were located on chromosomes 1D, 2B, 3D, 4A, 5A and 7A with each QTL explaining between 4 and 15% of the observed phenotypic variance. QTLs were contributed by both parents. In the ‘Cascades’בAUS1408’-derived population, QTLs from ‘Cascades’ were identified on chromosomes 2A, 2D and 7A with each QTL explaining between 12 and 18% of the phenotypic variance. Several markers were identified which are promising candidates for use in marker-assisted selection programmes. If one, two or three of these markers would have been used to select for black-point resistance in the ‘Sunco’בTasman’ population, then with one marker 34 of 39 resistant lines, with two markers 23 of 32 and with three markers 17 of 32 would have been selected. At the same time, 67 false positives obtained by selecting with one marker are reduced to 24 by selection with two markers and to 11 by selection with three markers. Similarly, if one, two or three markers are used to select for black-point resistance in the ‘Cascades’בAUS1408’ populations, then with one marker 25 of 31 resistant lines, with two markers 26 of 31 and with three markers 10 of 31 are selected. At the same time, 14 false positives are obtained with one marker are reduced to six by selection with two markers and no false positives are selected using three markers.

Notes: Recently there has been much interest in performing tomographic inversion on data acquired in seismic reflection configurations. Several approaches to dealing with the unknown geometry of reflectors have evolved, the most natural of which seems to be to parametrize them in a manner consistent with the velocity field discretization. the inversion may then be formulated to treat both sets of parameters equally, avoiding the possibility of in-built bias. One appropriate formulation may be a least-squares optimization with a priori and step-length damping terms, which may be accomplished by a multiple-parameter class subspace method.Unfortunately a standard, ‘naive’ application of such an optimization method appears to fall foul of trade-offs between reflector depth and near-reflector velocities. These are manifested in the poor reconstruction of the lower portion of test models from synthetic data. Considerations of determinacy, strategies for non-linear problems and regularization inspired the idea of a multiple-stage approach, in which successive stages admit progressively shorter scale lengths of variation in both velocity field and reflector. an algorithm implementing this approach demonstrates a significant improvement in the reconstruction of longer-wavelength components of test models. However the tests also suggest that the shorter-wavelength velocity-depth trade-offs at the reflector are unresolvable without further information.

Notes: Modern wide-angle surveys are often multi-fold and multi-channel, with densely sampled source and receiver spacings. Such closely spaced data are potentially amenable to multi-channel techniques involving wavefield propagation methods, such as those commonly used in reflection data processing. However, the wide-angle configuration requires techniques capable of handling very general wave types, including those not commonly used in reflection seismology. This is a situation analogous to that faced in cross-borehole seismics, where similar wave types are also recorded. In a real cross-borehole example, we compare pre-stack migration, traveltime tomography and wavefield inversion. We find that wavefield inversion produces images that are quantitative in velocity (as are the tomograms) but are of significantly higher resolution; the wavefield inversion results have a resolution comparable to that of the (qualitative) pre-stack migration images. We seek to extend this novel development to the larger-scale problem of crustal imaging.An essential element of the approach we adopt is its formulation entirely within the temporal frequency domain. This has three principal advantages: (1) we can choose to ‘decimate’ the data, by selecting only a limited number of frequency components to invert, thus making inversion of data from large numbers of source positions feasible; (2) we can mitigate the notorious non-linearity of the seismic inverse problem by progressing from low-frequency components in the data to high-frequency components; and (3) we can include in the model any arbitrary frequency dependence of inelastic attenuation factors, Q(ω), and indeed solve for the spatial distribution of Q.An initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly. This is related to the fact that the reconstruction is obtained from forward-scattered waves. Under these conditions, the method thus behaves much like tomography. A second test with a deeper, more extensive anomaly yields an image with the correct velocity polarity and the correct location, but with a deficiency in low and high wavenumbers. In this case, this is because the reconstruction is obtained from backscattered waves; under these conditions the method behaves not like tomography, but like migration.A more extensive test, based on a large wide-angle survey in south-eastern California and western Arizona, demonstrates a real potential for high-resolution imaging of crustal structures. Although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today, the images are sufficiently encouraging to warrant future research. The problem of local minima in the objective function is the most significant practical problem with our method, but we propose that appropriate ‘layer’ stripping methods can handle this problem.

Notes: We describe the use of aprotinin in two patients to control life threatening haemorrhage due to coagulopathy when other therapeutic measures had failed. We review the use of aprotinin and give a rationale for its use in acute coagulopathy.